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Published: Tuesday, 20 July 2021 05:22
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PT DSLG (define scaling lib group):

In previous section, we saw that PVT variations can be modeled by using derating on cells. Voltage and Temperature variations were modeled by using derating. Different derating values were applied to different cells depending on ir drop and temperature of the cell. We had 4 voltages that were applied depending on if the cell was on clock path or data path:

  1. Early Clock Voltage (EC) => shortest delay path for clock (fast clk)
  2. Early Data Voltage (ED) => shortest delay path for data (fast data)
  3. Late Clock Voltage (LC)=> longest delay path for clock (slow clk)
  4. Late Data Voltage (LD) => longest delay path for data (slow data)

Derates are inaccurate, and a lot of spice simulations have to be performed on different cells to figure out the value of derates for a given voltage drop. A lot of things are not accounted for when estimating derates, as it's very time consuming process. For ex, impact of voltage on drive strengths, input slews, output loads, pin caps, etc are not accounted for. We had to use derating, because we didn't have libraries for each and every voltage and temperature combination. However, if we did have continuous libraries for each and every voltage and temperature, then we could accurately calculate the delay of any cell, by figuring out it's voltage and temperature, and then calculating it's delay at that corner from the library. This would be much more accurate than the derate approach (process variations are still accounted for by using derating, it's only Voltage and Temp that we account for by using this method). This is known as the "scaling" methodology. This scaling flow from synopsys PT is called DSLG (define scaling lib group) flow.

There are 2 different techniques employed in DSLG:

1. Library scaling: Library scaling is a known technique that performs voltage and temperature scaling by interpolating data in libraries that was characterized at different voltage and temperature corners. This cross-library scaling
allows us to analyze timing, noise, and power at voltage and temperature values that are different from that of the corner libraries. CCS libraries are generally used for scaling as the scaling is more accurate. NLDM libraries may also be used, although accuracy will be lower.

For library scaling, following guidelines should be followed:

  1. All libraries should be checked by using Library Compiler Qualification System to make sure libraries an be scaled. All lib need to have identical cell names, pins names and identical arcs.
  2. Linking library that is provided via using "link_library" cmd (or using min_library to specify min lib too) is still provided and is used for linking the design. This link lib can be present in only one of the groups defined using "define_scaling_lib_group". Rest of the libs provided are used for scaling purpose only. In DSLG flow link_library has no special meaning (as all libs in a group have same arc, only the values of arcs change). link_library is used as a fallback library, when PT can't continue with DSLG flow.
  3. 1D scaling requires atleast 2 libs. General 2D scaling requires at least 3 libs. Temp and Voltage are treated as separate scaling dimension. PT currently supports 3 different types of scaling formation => 2^n on the grid, (2n+1) and (n+1). For single voltage domain, it doesn't matter, but when we have multiple voltage domain on same cell (such as level shifters)l, then scaling is more complex.
  4. Delay can usually be interpolated linearly. But for setup, hold, recovery, removal, min pulse width (MPW), min period (MP) constraints, etc., more accurate non linear interpolation is done. 
  5. For single voltage design running in single mode, we don't need to specify PVT cond, as there's only 1 lib to use. We do provide op cond for PVT, but the values in there aren't used for anything.

Besides modeling voltage and temperature changes, scaling reduces the number of libraries required for the analysis of multivoltage designs and therefore reduces the library characterization effort. Usually only voltage scaling is done, and derating is still used to account for temperature variations. Since Temperature variation is much less (only +/- 15 degrees or so), and scaling is not very accurate for this (as temperature and delay don't follow a monotonic relation at low nm tech), we don't usually do temperature scaling.

PT cmd: define_scaling_lib_group <libs> => To define a library group for scaling. We use this cmd multiple times to define multiple library groups to cover different portions of the design. We need different groups for diff libs that contain diff kind of cells as svt, lvt, level shifter, special cells, hard IP, etc. We can't scale data from lvt to svt or vice versa. So, we can't have these in same group for scaling purpose. Moreover, each library can be part of only one library group.

pt_shell> define_scaling_lib_group {lib_0.9V_0C.db lib_1.05V_0C.db lib_1.3V_0C.db} => This creates a lib grp with 2 libraries used to scale data from 0.9V-1.3V. PT reports a messages as "completing scaling lib gropus, loading db files ... scaling complete". That means all libs were consistent and scaling could be performed. SLG-308 and SLG-318 errors indicate that some arcs in link lib aren't there is scaling libs, and scaling can't be done. These will need to be fixed or else flow will fall back to link_library for timing.

2. Exact matching: As an alternative to library scaling, we can use library data in an exact-matching flow, where operating conditions must exactly match one of the libraries. In this flow, PrimeTime chooses a matching library based on the operating conditions applied to the specific design cell instances. If no matching library is found, PrimeTime issues an error message (or SLG-216 warning) and does not perform scaling. This warning helps you detect mistakenly applied operating conditions. Exact matching is used in conjunction with scaling. We specify exact matching for memories, phy and other hard macros, which don't have well defined relationship with voltage and Temperature (also internal paths are hidden, so hard to say how do the interface paths scale). In this case, we just do a exact match

PT cmd: define_scaling_lib_group -exact_match_only <libs> => same cmd as above, except we need to add the option -exact_match_only"

pt_shell> define_scaling_lib_group -exact_match_only {lib_0.9V_0C.db lib_1.0V_0C.db lib_1.1V_0C.db} => Does exact match only. If no matching corner library is found, the tool issues SLG-216

3. Best matching: As an alternative to exact matching, we also have a best-matching flow. Here, closest lib is found (when an exact match is not avilable) and that lib is used for analysis. Syntax same as above (This option not yet available in PT docs as of 2020).

pt_shell> define_scaling_lib_group -best_match {....}

NOTE: There's an extra option "-exclude_rail_names" to ignore certain rails for scaling or matching purpose (for rails that are irrelevant for timing analysis on an IP. i.e SRAM voltage inside an IP, where SRAM paths are not exposed to IP pins, we can exclude SRAM voltage power rail for matching purpose). This option not yet available in PT docs as of 2020.

pt_shell> define_scaling_lib_group -best_match  -excluded_rail_names {  VBB VPP BIASNW VDD_SRAM ... } { lib1.db lib2.db ... }

Additionally, we can set this user attribute to tell the tool to not scale certain IP, etc:

pt_shell> set_user_attribute -quiet [get_lib_cells */IP_SRAM] is_scalable false

DSLG flow:

1. Read library: link library as before with one of the timing library. In DSLG flow, link_library is just a fallback library to use in case something goes wrong with "scaling lib", and DSLG flow is not run.

2A. Read netlist:

  • Read verilog netlist: read_verilog ...
  • Set DSLG libs: define_scaling_lib_group <libs> => link library above may be used at most in one these groups. When finished, it prints "scaling complete" message
  • report_lib_groups -scaling -show {voltage temp process} > ~/dslg_grp.txt => Once lib groups are defined, we can report all scaling groups defined above , by using report_lib_groups cmd. It shows all groups along with the libs, their voltage+Temperature that we are using for that group. One of the groups is used for each cell in design. For seeing summarized info, just use "report_lib_groups -scaling". As an ex, o/p will show all SVT stdcells in diff voltage libs in one grp, all LVT cells in diff voltage libs in other group, each hardIP with diff voltage libs in another group and son. There may 10-100 of groups that it may show depending on how many groups were defined (which is dependednt on how many diff kind of lib cells were there).
    • sample o/p: group 1: tsmc_stdcell_svt_0p9v_m25c tsmc_stdcell_svt_1p1v_m25c group 2: tsmc_stdcell_lvt_0p9v_m25c tsmc_stdcell_lvt_1p1v_m25c and so on ...
  • linking: link cmd not needed as above cmd does linking, if linking wasn't done already.
  • list_libraries > ~/all_libs.txt => lists al libraries.. see detail of cmd in "PT Object access functions" section
  • report_design => lists op cond. see detail of cmd in "PT-OCV" section

2B. Read parasitics file => Read spef file as before.

3A. Read constraints: Read all constraints as FP, MCP, SCA (set_case_analysis), etc.

3B. Setting Temp and Voltage: Here we have to set Voltage and Temperature for each cell in design. Previously we used set_operating_conditions cmd to set op_cond for the design. That specifies PVT for the whole design (either 1 set of PVT or 2 sets of PVT depending on analysis mode). For OCV flow where we needed to specify diff PVT for each cell, we specified diff derating for each cell in design. Here in DSLG flow, we use a combination of derating and scaling. First we set voltage and temperature for each cell using set_voltage and set_temperature cmds, and then account for process variations using derating:

  • set_operating_conditions <WCCOM> => sets op cond. See in "PT - OCV" section for details
  • set_voltage => defines voltage on pwr nets or pins. For pins, we specify the cell name and the power pins of that cell to apply the voltage. We can  specify all 4 kinds of voltage for a power net - early clk/data, late clk/data depending on whether the cell is on clk path or data path. By default voltages apply for both data and clk. If we want to specify a diff voltage for clk path, we need to use option "-clock". By default voltages apply for both early and late. If we want to specify a diff voltage for late, we need to use option "-min". min or max refers to path delay here, so min means min delay (i.e fastest case), while max means max delay (i.e slowest case). There's a -dynamic option that specifies portion of voltage change that varies with frequency (i.e ripple in voltage supply). Frequency o this ripple is several clk cycles. This dynamic portion is considered during capacitive coupling analysis and various pessimism removal optimizations. This option is not used generally.
    • syntax for least voltage applied to both data/clk paths: set_voltage <max_delay_voltage> -dynamic <dyn_max_delay_voltage> -object_list <list_of_power_nets> => These options are for max delay (i.e slowest path). Add -min option to specify voltage for min delay (i.e fastest path). Applies to both clk and data if -clock not specified.
      • ex: set_voltage 0.540 -object_list {VDD_SOFT VDD_ON} => Here 0.54V is specified on power net VDD_SOFT, VDD_ON for both clk/data and for both early/late paths
      • ex: set_voltage 0.540 -min 0.562 -object_list VDD_SOFT => Here 0.562V is applied on early path (both clk/data), and 0.54V on late paths (both clk/data).
      • ex: set_voltage -clock 0.540 -min 0.562 -object_list VDD_SOFT => Here max/min delays are applied only on clock path. For data path, max/min delays are applied if set_voltage used without "-clock" option.
    • We also have an option to set voltage directly on pg pin of a cell, if we want to override what's provided on power net.Here we use -cell option to specify cell list, and -pg_pin to specify each pg pin of cell.
      • ex: set_voltage 0.04 -min -0.05 -cell I1 -pg_pin_name GND => sets "GND" pin of cell "I1" to 0.04V and 0.05V
      • ex: set_voltage -pg_pin VDD_SRAM -cell [get_cells I_top/sram_cell] 0.75 => Here we are setting pg pin of sram directly with a voltage. NOTE: voltage value is specified at end of cmd, and not in middle.
    • The way to use "set_voltage" is to first read in UPF file (which specifies power domain and power connections). Then specify voltages on these power nets or on each instance power pin.
    • In case you don't have an UPF file, you will need a pg verilog netlist, which has power pin connections for each instance of cell. Then we can use set_voltage to specify voltages on these power nets or on each instance power pin.
    • NOTE: since voltage may not be set for each every cell in design, there is a voltage priority sequence that's followed in case of voltage setting conflicts or voltages not defined explicitly:
      • Firstly, default supply voltage set via "voltage_map" in liberty file is taken as voltage.
      • If set_operating_condition is used, then that is applied to the design.
      • Then if set_voltage is applied on supply net, then that takes priority over the previous two. However, if set_voltage is applied on PG pin of a cell, then that takes highest priority.
  • set_temperature => It's the counterpart of set_voltage for setting temperature. We can specify min and max case temp for cells on the design, so that are timed and optimized at the specified temperature. min and max refer to min delay (best case) and max delay (worst case). Min/Max case are used for early and late paths.
    • syntax: set_temperature <max_case_temp> -min <min_case_temp> -object_list <list of cells>
      • ex: set_temperature 125 -object_list [get_cells "I1 I2"] => this specifies both min and max case temp on this cell to be 125C.
      • ex: set_temperature 125 -min 25 -object_list [get_cells "I1 I2"] =>here min_case (best_case) temp is 25, while max case (worst case) temp is 125 for both cells.
    • NOTE: most of the times, we don't use temperature scaling, so we just use derating numbers, and not use this cmd at all.
  • check_timing: CMD => check_timing -override_defaults operating_conditions => Very imp to run this cmd. This operating cond check issues warnings as SLG* which need to be fixed. For scaling lib groups, it issues warnings if operating condition is set beyond the range of the libraries in the scaling group. For exact-matching library groups, issues a warning when operating conditions do not match any of the libraries in the scaling group For cells that are not part of either exact matching or scaling groups, it uses operating condition in link lib, and if different, it issues warnings.

4. Generate reports => generate timing reports and all other reports for analysis. NOTE: most of the lib reporting cmds that we used earlier, report link_lib when used in DSLG flow, when in reality the lib being used for timing are "combo of scaled libs" or "best matched lib" which may be different than "link_lib".

Additional helpful reports for DSLG:

  • report_delay_calculation => This cmd shows how the tool scales data for delay calculation. When used with the -thresholds option, it also reports cell instance operating condition and rail names. For example:
    • pt_shell> report_delay_calculation -from [get_pins cell/A] -to [get_pins cell/Z] -thresholds => shows all rail voltages and op cond.
      • NOTE: it shows linking lib at the top of report, which is just some lib that was used for linking. Then below it, it does show all scaling libs being used, and those are the one from which it extracts the delay at the voltage needed. It will show the delays, but it won't at what voltage level those delays were calculated. To see voltage level on the cell, we need to use other cmds below.
  • report_power_pin_info =>This is the most useful cmd to find out voltages on pg pins of any cell. It shows PG pin connections for that cells (i.e VDD pg pin connected to VVDD_CHIP, etc). It shows voltages all 4 possible voltages to be used depending on whether's it's on clk or data path => clock max/min delay, data min/max delay (early/late voltages that we talked above)
  • report_power_net_info => Once power nets are assigned voltages, this cmd may be used to dump out op voltages for all power nets in design. Even though PT docs show this cmd, and "man report_power_net_info" shows info for this cmd, but it errors out with "unknown cmd" in PT 2021 versions.
  • report_timing -voltage -derate => This is the best way to know supply voltage and derating being used for timing purposes on a cell is by running "report_timing" with option "-voltage" and option "-derate". If set_voltage cmd isn't used to set worst_case/best_case voltages, then derating numbers being used will be larger to account for voltage variations too (In this case, it uses same voltage for all paths, but uses derating to model for wc/bc voltage). Derating already accounts for process and Temp variations, with dslg it doesn't need to account for voltage variations.
    • setup timing: pt_shell> report_timing -thr top/cell_a -delay max -voltage -derate => Since this is max delay (setup), this will show min voltage on launch clk and data, and max voltage for capture clk (used for all cells in clk/data path).
      • launch clk path => LC (late clk). Lowest voltage applied accounting for off chip IR drop and on chip IR drop. We don't account for any voltage reliability drop for clk path, since clk path is always switching, so Vth degradation doesn't happen. This voltage is slightly higher than data path voltage, since voltage droop due to reliability isn't included here. ex: voltage applied may be 1.1V. For derate, it will show derate of >1, i.e 1.02 (i.e 2% slower path). NOTE: derates will be much higher if different voltages aren't applied to different paths. Here derates only model process and temp variations.
      • data path => LD (late data). Lowest voltage applied accounting for off chip IR drop, on chip IR drop and any voltage reliability drop (due to cells not switching all the time, Vth degrades). This voltage is slightly lower than voltage applied to launch clk path, as extra voltage reliability drop is accounted for here. This is the lowest voltage that chip can ever see. ex: voltage applied may be 1.0V. For derate, it will show derate of >1 but slightly more than derate in launch clk path, i.e 1.05.
      • capture clk path => EC (early clk). Highest voltage applied on this path accounting for only off chip IR drop. This is the highest voltage that chip can ever see. ex: voltage applied may be 1.2V. For derate, it will show derate of < 1, i.e 0.96 to indicate it's 4% faster
    • hold timing: pt_shell> report_timing -thr top/cell_a -delay min -voltage -derate => Since this is min delay (hold), this will show max voltage on launch clk and data, and min voltage for capture clk (used for all cells in clk/data path). Ex: Voltage shown may be 1.1V, which is higher than one shown above.
      • launch clk path => EC (early clk). Highest voltage applied on this path accounting for only off chip IR drop. This is the the same voltage/derate as on "capture clk path" in setup timing. ex: voltage applied may be 1.2V. For derate, it will show derate of < 1, i.e 0.96 to indicate it's 4% faster
      • data path => ED (early data). Highest voltage applied on this path accounting for only off chip IR drop. This is the same as the voltage on launch clk path. ex: voltage applied may be 1.2V. For derate, it will show derate of < 1, i.e 0.96 or same as for launch clk path. 
      • capture clk path => LC (late clk). Lowest voltage applied accounting for off chip IR drop and on chip IR drop (no voltage reliability drop). This is the same voltage as on "launch clk path" in setup timing. voltage applied may be 1.1V. For derate, it will show derate of > 1, i.e 1.02 or same as for launch clk path in setup timing. 

 

report_lib <lib_name> => Here we can check for op_cond defined in specified lib. Not very useful, as we can do that by manually looking into lib file. See detail of cmd in "PT Object access functions" section

report_cell <cell_instance_name> => this shows ref lib cell, OC used, voltages etc for given cell. In DSLG flow, OC cond shown are from This is very helpful cmd. see detail of cmd in "PT Object access functions" section

shows ref

 

ame as regulat PT flow until read_

More PT scaling related useful cmds:

1. report_lib_groups: Once lib groups are defined, we can report all scaling groups defined, by using report_lib_groups cmd.

pt_shell > report_lib_groups -scaling -show {voltage temp process} > ~/tmp1.txt => It shows all groups along with the libs, their voltage+Temperature that we are using for that group. One of the groups is used for each cell in design. For seeing summarized info, just use "report_lib_groups -scaling"

2. report_delay_calculation => command. The report shows the results using the link library, then the scaling library group results if applicable and valid.

set_voltage

set_operating_condition

 

 

 

Details
Published: Monday, 12 July 2021 06:47
Hits: 2878

Electronics:

This sections deals with all electronics and where to buy them for cheap. There are tons of electronics that you can buy, but most of them have no utility or are a subset of some other electronic, doing the same thing. I think, a laptop and a phone are electronic that justify their existence. Apart from that a TV or projector is nice to watch and get entertained on big screen (although for most people, a laptop screen is big enough to satisfy them). But since TV and Projectors have gotten so cheap, it won't make a big hole in your pocket. Then there are hard disk or USB sticks that you might need for making a backup of your data. Everything else out there under the pretext of smart electronics is non sense junk. I buy this junk too, so I've listed them below :(

Lastly, the real innovation in electronics for the past decade has been LED bulbs. Those are worth your money more than anything else, as they really have innovated if you know what innovation means !!

 

 

Laptops:

Laptops shouldn't cost more than $300 in general. You can usually get very good laptops in this price range. Walmart Black friday sales are one the best times to buy these sub $300 laptop. Other than that, ebay seller "vipoutlet" also has refurshied (but like new) laptops for sale every once in a while. I've bought multiple laptop, TV from them, and they all looked like new. They also have 20% off coupon from time to time, which can fetch you a pretty good laptop for less than $250. I've come to know that vipoutlet is a resale arm of walmart (i.e items returned at Walmart are sold here), so all the items are inspected and most of them are in nearly new condition.

This is the link to vipoutlet store: https://www.ebay.com/str/vipoutlet

Other good place to buy laptop is at Walmart. They have decent sales all year along, and you can always return it without any hassle in store. Sometimes, you will find incredible deals on laptops by looking on brickseek for laptops on clearance. BestBuy used to have some good sales, but as of 2021, I haven't found a single laptop priced to sell for the last 2-3 years (since 2019).

DELL: One other good place to buy laptop is www.dell.com, as they have sales all year around. Around BF, you can get a lot of good deals. Their laptops are sturdy. Their customer service is also very good. I've one Dell laptop in my possession that I bought used for $95. It has been running fine for the last 5 years with Linux installed on it. These laptops are built to last based on my limited experience. Look in "stores" section for more details.

When you buy a laptop or a desktop, it has 2 kinds of memory. One is the permanent memory, which is the hard drive, while the other one is volatile memory which is the DDR Memory. Read in "Memory section" for more details.

Performance of your computer is mostly determined by the processor type and the DDR memory connected to it.  Laptops with large DDR memory and faster Hard drives with a decent processor run faster than those with lower specs. A decent DDR memory requirement is 8GB (4GB DDR memory laptops run too slow with Windows, though they do just fine with Linux. However if you open a lot of tabs in Firefox, you may see that 4GB memory is used up completely, and laptop comes to a near stall). Regards to Hard drive, a faster Hard drive improves performance. SSD are faster than mechanical Hard drive, so go with SSD if possible. A decent Hard drive size is 500GB or so. You will never need more than 500GB (unless downloading popular paid games). If you do run out of space, start compressing your files using open source programs as gzip, etc. That will reduce your file size by a factor of 5. If you still run ou of space, buy some external Hard drive or USB drives, those are really cheap. You can get 1TB drives for <$80 as of 2021.

It's possible to replace both DDR memory and Hard drive in most laptops. Replacing DDR memory is super easy and is a 10 minute job. Replacing Hard drive is tricky, and not always possible. So, I always try to buy a laptop with low DDR memory (since they are usually cheaper), and then replace the DDR memory myself (buying 2X8gb memory modules cost about $50). Don't bother with Hard drive. It has a little effect on how much time it takes for your laptop to start. Most of the laptops I've are with Hard drives, and I never see any issue with performance. See below for details.

So, for extra $150, you can buy 16GB DDR memory and 1TB SSD drive, making your $250 laptop a power house.

 

 

DDR Memory Modules:

You will need to buy DDR memory module if you plan to replace the DDR memory for your laptop to get better performance. Once you get to 16GB of DDR memory, adding additional memory doesn't help, as 99% of the users are never going to exceed 16GB of memory requirement, no matter how many apps you have open. Laptop memory are usually SODIMM, so look for those modules only. Many memory modules are exclusively for desktop, they won't fit in a laptop.

You can get 4GB memory modules for around $20. So, for 8GB memory, you may buy 2X 4GB modules for $50 or less. For 16 GB memory, you can buy 2X 8GB modules for $80 or less (amazon often has these on sale for less than $50). I would recommend buying 2X 8GB as these are usually on sale and heavily discounted. You can even even get 2x16GB for less than $100. You don't have to go for the fastest speed, as speed of memory has negligible effect on performance for everyday activities. Below is a recent deal on amazon for a fast 32GB DDR module. 2X 32GB modules (for a total of 64GB) on sale for $286. Going by the rate of $10 for 4GB, it should be around $10*16=$160 for 64GB. So, it's very expensive to start with, as these bigger modules sell for a premium. Of course you never need these large memories for any laptop (and lower end laptops may not even support such large memories). So, don't go for a deal, just because a lot of sites are heavily promoting it. It may still be a pretty bad deal for your laptop.

  1. 2X 8GB:
  2. 2X16GB:
  3. 2X32GB:

Usually you need to buy 2 modules of same size, as most laptops have 2 memory slot. The easiest way to find out compatible memory for your laptop is to take out existing memory, look at the model number, brand and size. Then look for same brand, or some other brand similar is size. Not all processors support, all Memory type, so you may be limited in what DDR memory modules you can put in there. You don't need to replace both memory modules at same time, you can have 2 different brands. Although it's recommended to have both modules the same. I've never encountered issues myself having 2 brands in the 2 slots.

PRICE:

2021: Good Price to buy DDR module is around $2/GB - $3/GB as of 2021.

2023: As of Apr 2023, price for 2x16GB modules is ~$60, or < $2/GB. These prices are crashing hard.As of July, 2023, good price to buy is $1/GB.

 

 

Hard Drives:

There are 2 kinds of hard drives on market.

  1. Mechanical Hard drives: These are traditional ones and have mechanical moving parts, i.e they have a spinning disc, motor, moving pin, etc. These hard drives are the ones that used to be in laptops, and make a sound when spinning. They have spinning speed specified as 5400 rpm or so. If the name of a hard drive doesn't say "SSD" on it, that means it's a mechanical hard drive. However, these hard rives are very susceptible to damage due to hard disk falling down, getting knocked off, getting dirt/moisture, etc. I had 3 of these external hard drives that were just used for archive purpose couple of times a year, and they all died within 2-5 years. They die so suddenly, that your backup may be lost forever, unless you made a backup of the backup. I've completely given up on mechanical hard drives, since they are so unreliable and die so fast. Once you lose data, you will never buy these again. Also, it's impossible to recover data without paying hundreds and thousands of dollars to the manufacturer. Surprisingly, the mechanical hard disk that come pre attached in a laptop, last much longer. So, not sure why the quality of these external hard disk is so poor. These have gotten very cheap, and you can grab a 5TB HD < $100. Deals abound all the times on amazon, bestbuy, walmart, etc.However stay away from these even if they go for free.
    1. One such deal is here: https://slickdeals.net/f/15183859-5tb-wd-easystore-external-usb-3-0-portable-hard-drive-89-99-free-shipping?src=frontpage
  2. SSD Hard drives: These are counterpart of mechanical hard drives, but with no moving parts. They are similar to USB sticks, where solid state transistors store data, so it's like DRAM, but with permanent storage. The used to be very expensive (about 10X the price of mechanical hard drives), but as of 2021, you can find 1TB SSD disk for < $100. As of 2022, 2 TB SSD are around $100. Most of the time, you don't need more than 1TB for archiving purpose. If 1 TB gets small, compress your data before you store it on hard drive. then uncompress it while using. Compression/uncompression is very fast, and save you 2X-5X the space.  Other thing to watch out for an SSD is how many times can you write to an SSD, before it fails. This is expressed as how many TB can you write on it. Most 1TB SSD have 500 TBW rating meaning you can write 500TB of data on it, before it will start degrading. Since the drive size is only 1TB, it implies you can write the whole drive 500 times over it's usable life. This sounds like a short life, but writing 500 times on that full size will usually take 10 years or so with normal use. NOTE that the SSD hardware/software inside will make sure to spread writes evenly over all locations, so you don't end up writing unevenly - i.e too many writes to one particular location, and too few writes to other. There are 2 kinds of SSD hard drive interfaces:
    • HDD type interface: This has same size and same connector pins as you would see in a "mechanical hard drive". That makes it easy for replacing a "mechanical hard drive" from an existing laptop/desktop with this SSD drive. People usually buy these to make their older laptops run faster, as SSD even with this slower interface are still 10X faster than spinning drives. These slower i/f are needed to keep compatibility with existing connectors.
    • M.2 interface: This is the interface that is supported by all newer laptops that come with SSD in them. This looks more like DDR memory modules, and has connectors on 2 short sides. This interface supports many protocols over it's pins, most common being PCIE Express protocol and less common being SATA. On this PCIE Express architecture, support for NVMe (Non Volaile Memory Express) spec is provided. Before NVMe, SSD were made using PCI Express bus, but using non std interface spec. NVMe came as a standard, which made it easy to have just one driver for supporting SSD communication. Support for NVMe comes from hardware controller attached on the SSD side. These kind of SSD are sold in market as "M.2 NVMe PCIE SSD". These are the one that you should buy if your laptop has a M.2 slot.

As we noted above, speed of your laptop is determined by the speed of your hard drive (NOT the size). Since these SSDs ar 10X faster than mechanical hard drives, your laptop boots up within seconds, and never seems to be crawling to death (that usually happens beacause older mechanical hard drives over time get very slow). If storing files is is your primary purpose, then an external hard drive would be better as it would have longer life.

Brand wise people seem to prefer Crucial and Samsung for Hard drives, as they have very reliable performance and are top of the line. Samsung EVO series is usually more expensive than Crucial MX 500 series, so get Crucial MX 500 as difference in performance and reliability is negligible.

Other thing to note is that DDR memory go for $10 for 4GB or $2.5K per TB. SSD Hard drives go for $100 per TB, while mechanical hard drives go for $20 per TB. So, DDR memory modules are about 100X more expensive than mechanical hard drives for same stiorage capacity. This is  all due to differences in design of Volatile and Flash Memory, and Volatile memory using 6 Transistor design compared to 1 transistor design for Flash. and changes to tech to make the memory non volatile.

Replacing or upgrading with an SSD:

If you have a older laptop, you may have HDD, or a SSD. You may also have extra slots in your laptop for an additional HDD or SSD. Upgrading your laptop to take advantages of SSD is very simple.

  1. Adding Memory to Extra slot: In such cases, you should use the extra slot and install a new SSD. The extra slot may either support 2.5 inch memory or M.2 memory. If you have HDD currently, then the extra slot will support 2.5 inch HDD/SSD, while if you have M.2 SSD currently, then extra slot will support either 2.5 inch SSD or M.2 SSD. Look what your laptop by searching on youtube and how to replace it.
    1. No cloning or anything else is required. Just open the laptop, put right kind of 2.5 inch or M.2 SSD. 2.5 inch SSD can use exiting screws and cover, so nothing new to buy. For M.2 SSD, you may need to buy "bracket" to hold the SSD in place. sometimes, these are provided with the laptop, but generally ot. You can buy them on ebay for $2-$3. No need to buy heastsink, it's not needed.
      1. Bracket for Dell laptop (4 will cost around $11) => https://www.ebay.com/itm/284399831280
    2. Attach the memory to newly bought bracket (which itself should be attached to the motherboard), close the cover, and turn on your laptop. Search for "format partition" on windows. You will have to format the partition, before Windows will start seeing it (it's not automatic).
  2. Replacing Memory in Existing slot: In such cases, we want to replace the existing hard drive or existing M.2 Memory. This is tougher, as all data and OS is on existing HDD or SSD, so we'll need to make sure that all this data and OS is transferred to the new SSD.
    1. Manufacturers of SSD provide free clning software. Use that to clone all data from existing drive to new SSD. New SSD will need to be attached to the USB port or some other port of the laptop, so that copying can take place between the old and new drive. Make a backup copy of existing drive in a spare standalone USB or some other storage device. This will save your day, in case something goes terribly wrong, and data gets corrupted on existing drive.
    2. Once cloning is done, open the laptop, replace the existing HDD or SSD with the new one. Restart the laptop, and it should boot up seamlessly.

PRICE:

2021: Good Price to buy SSD Hard disk is around $0.07/GB - $0.08/GB as of 2021.

2022: As of 2022 end, you may get these for $0.05/GB, so a 1TB SSD for $50) - So, these are about 50X cheaper than DDR modules of same capacity.

2023: 1 TB SSD is going for ~$35 on amazon. So, prices are crashing hard.

 

 

Monitors:

Monitors are not really needed if you have laptop. Get a 17 inch laptop if you need bigger screen. Sometimes you do need a > 22 inch screen or dual screen. In that case, attaching a monitor to a laptop makes sense. You can easily get a 1080P monitor with 27 inch for < $100. 4K monitors are expensive and usually run north of $200. My price target for any 1080P monitor is around $50.

 

 

USB memory sticks:

These USB memory sticks are similar to SSD hard disk as far as physics of storage is concerned. They have USB 2 or USB 3 as their transfer interface. USB 3 is faster speed, so those cost more than USB 2 sticks. USB 2 sticks are mostly obsolete now. These are also very reliable. However, their sizes are limited, with max size memory stick that you find being limited to 256 GB or so. Most of the memory sticks that you see on sale are smaller sized memory sticks as 32GB. As of 2021, you can find 128GB memory sticks for < $10, with 32GB memory sticks going for a dollar or two. I love USB memory sticks for multiple reasons:

  1. They are cheaper than SSD. You can find 10 USB memory sticks (each 128GB) for < $100, while equivalent SSD for 1TB will cost at least $100.
  2. They are very reliable. I had around 10 USB memory sticks for more than 10 years now, and none of them have failed. By contrast, mechanical hard drives failed with 100% certainty in first 5 years. I would suggest to store all your archive data in these USB memory sticks. Of course you can't store everything in one stick, but if you have around 10 of them, you can store all your data by compressing them.

USB interface: When looking for a USB stick, try to get with USB-C interface. Those are usually expensive, but as of 2022, you can get them for almost the same price as USB-A  interface ones. Since most laptops/phones now come with USB-C interface, it's future proof. USB-A ones are OK to get when on fire sale, as most newer laptops still have at least 1 USB-A interface (though this might change in next few years, possibly by 2025)

PRICE: Good Price to buy USB Memory sticks is around $0.10/GB as of 2021. Of course 4GB memory stick is going to be more costly (per GB) than larger sized stick. A 4GB memory stick for $1 is a good price, as you can use it to burn Linux OS and keep it burnt for ever. These are slightly more expensive than SSD Hard disk.

 

 

SD Memory cards:

These are similar to USB memory sticks. But instead of being a stick with USB interface, they are meant to be inserted in cameras, with a SD interface for memory. Their cost is similar to USB memory sticks as it's the same technology. I use these memory sticks too for storing data too (instead of just using to store pics). They are equally reliable as USB memory sticks. They come in 3 different physical sizes asshown below:

  • Standard SD: This is the largest size measuring 32mm x 24mm. These cards are not sold anymore.
  • Mini SD: This is the smaller size measuring 21.5mm x 20mm. This is the slot you see in your PC and in your camera for inserting SD cards,
  • Micro SD: This is the smallest size measuring 15mm x 11mm. This is the most common SD card being used. It's used everywhere in phones. You should always buy a Micro SD card that comes with a mini adaptar. Mini adaptar allows this Micro SD to be inserted into Mini SD slots, so that you don't have to buy a separate Mini SD card to use in your camera or laptop. 

Here's one recent deal for SD Memory cards at Costco:

 PRICE: Good Price to buy SD memory cards is around $0.10/GB as of 2021. These are same price as USB memory sticks.

 

 

Phones:

Phones shouldn't cost more than $100, and that also for a very powerful phone. Many times your phone provider (Tmobile, etc) allow you to buy a phone for free via 24 month monthly credit, but you still have to pay sales tax. Those phones are decent phones, but usually cheap ones. You end up paying around $30-$40 in taxes itself (depending on your states sales tax rate), so I avoid buying these from carriers. Tmobile usually has offer for free phone by exchanging a used ones. You can buy these elgible used phones for $10 on amazon or ebay, and use that to get a new phone. One such phone is here: https://www.amazon.com/dp/B084GXS58R. Net cost might be $50 or so after accounting for everything. ebay is another place to buy cheap refurbished phones from authorized sellers.

I look for 3 things when buying a phone: a replaceable battery, a replaceable SD card and of course a low price. You don't need a high end phone with fastest processor, as phones from 20 years back still work as phones for making calls, texting, etc. Chips have gotten 1000X more powerful in the last 20 years, and there is nothing that we can do on a phone, that requires 1000X more computation. It's still just making calls, getting texts and browsing internet.

  • Battery: Unfortunately very few phones have replaceable battery now a days. LG V30 was the last phone with replaceable battery. There are few older phones from Samsung that have replaceable battery. You need replaceable battery to keep your phone running beyond 4 years, as batteries die within 4 years. Replaceable battery are also good to keep as spare, so that if your battery dies in middle of no where, you can swap the dead battery with spare one and keep going (instead of waiting to find a charging spot).
    • UPDATE 2024: No more phones with replaceable batteries exist anymore.
  • Memory card: You may find a lot more phones with replaceable SD card than the ones with replaceable batteries. Replaceable SD card for your phone allows you to increase the memory size of your phone. A phone that has soldered memory card, charges you a lot of money to go to a larger sized memory (~$200 or so). if you have replaceable memory card, you can just buy a 256GB card for $25 or so, instead of paying $200 more. A replaceable memory SD card is also very handy to move contents from your phone to your PC, as you just take out the memory card, transfer all the contents to your PC, and wipe out the card. With soldered memory cards, I always spend a lot more time and effort transferring content to my laptop.
    • UPDATE 2025: Most motorola phones allow you to add Memory cards up to 2 TB. Apple, Google and Samsung phones do NOT have memory card slot any more.
  • USB-C Port: Look for a phone that has USB-C port, as those charge the phone fast, and chargers for USB-C are getting cheap now (<$10). The USB-C cable as well as the charger come with the phone most of the time (unless you are buying an expensive phone). Also, 1 cable and charger can work for all phones that has USB-C port, so it's convenient to carry just 1 charging accessory for all phones.
    • UPDATE 2025: All phones now have USB-C port.
  • 4G vs 5G: 4G and 5G refers to the generation of cellular transmission used. Look in "cellular standards" section for details. Look for a phone with 5G since prices have come down a lot for 5G phones. 4G phones are the older ones, produced before 2020. For me, 4G phones work just fine, as I'm not on the road for long, and don't use internet a lot. Personally, I haven't noticed speed difference when browsing on 4G vs 5G. However, 5G makes your phone future proof, so buy it if you can get one for < $100. Prices for 5G phones will possibly come down to < $100 by 2023. For now and for next few years (as of 2022), 4G phones will suffice.
    • UPDATE 2025: Almost all phones support 5G now. Few older models from 2024 and before may support 4G only. Be careful and read the description before buying an older model phone.
  • GSM vs CDMA: Phones in USA used to either work on CDMA or GSM for pre 4G tech. T-mobile, A&T used GSM, while Verizon used to use CDMA. Sprint also used to have CDMA phones, but with it being a part of T-mobile now, it will be using GSM (CDMA will be phased out over time) GSM phones had sim cards, while CDMA phones were tied to the carrier with no sim cards to switch. These CDMA phones won't work in countries like India, since you can't switch SIM cards (GSM phones were fine). Now, all phones starting from 2018 onwards have chips for 4G and 5G, which don't rely on GSM or CDMA, but have common 4G-LTE chips or 5G NR chips (since that is what all carriers in USA support). All these phones also support 2G tech (GSM or CDMA) as fall back method which may have issues depending on your phone type. But if you ignore the fall back method, they should all work fine in 4G. In conclusion, whenever you buy a phone, buy a phone with a SIM card (i.e newer phones made in 2018 and beyond).
  • UNLOCKED: Always try to buy unlocked phones which cost a little bit more than locked phones.Unlocked phones are easier to work with any carrier, as they don't have any software tied to a particular carrier.
    • Tmobile: If you are with T-mobile, you are in luck. You can buy a T-mobile locked phone, which usually sell for lower price than locked phones. T-mobile will allow you to unlock the phone, after a month or two of service for free. Never hurts to save a few extra bucks.
    • Other carriers: Most will allow to unlock after 1 or 2 months of service. Check the details.

IMEI (International Mobile Equipment Identity) number: Many times when getting tech support for your phone or activating a new phone, you will be asked for IMEI number of your phone. IMEI number is a unique identification or serial number that all mobile phones and smartphones have. GSM phones have IMEI number while CDMA phones have MEID number. It is normally 15 digits long. It's tied to the device and has nothing to do with your phone number or your carrier. IMEI number reveals a lot of hardware details about your phone, and phone carriers may enable/disable phones based on IMEI number (i.e if the phone is lost or stolen). It's always a good idea to keep IMEI number of your phone written and stored in a safe place, incase your phone is lost.

There are several ways to get a IMEI number: Some of these are:

  • To get the IEMI number, dial *#06# (on the keypad of your phone), and it will pop up a box with IMEI number.
  • Under "settings" section of phone, you will find something similar to "About phone". This usually has the make/model and IMEI number.
  • If that doesn't work, you can just look on the sticker on the box, which will show the IMEI number.
  • If your phone back cover may be taken off, then the back side (right under the battery pack) also has the IMEI number written on it.

Here are few good phones I've bought in the last couple of years from ebay, amazon, bestbuy, MVNOs, etc:

  • Motorola family of Phones: All motorola phones have worked flawlessly for me. As of 2025, buy one with > 4GB RAM, and > 64GB memory. Ideally shoot for 8GB RAM and 128 GB memory. You can always increase memory with SD card, if the phone allows a SD card. Moto phones from 2023 and before are usually 4G, which won't work on 5G, so avid phones from those years.
  • LG family of Phones: Since LG has gotten out of phone business as of 2022, there's no rreason to buy LG phones anymore. It was good to get them on discount in 2022/2023. As of 2024, you can get motorola phones for $100 or so.
    • LG V20: https://www.ebay.com/p/18007923729?iid=112731504843 => This is the last LG phone with replaceable battery. All LG phones since LG G series (LG G2, G3, G4, G5, V10, V20, etc) have this bootloop issue where the LG logo will appear on powering up, and this logo will not go away. The bootloader is just looping around, and going nowhere. Each and every phone that I bought from LG had this issue, with the exception of V20 (so far). The phone may show up the issue in a year,or 2 year. So, you can still use the phone for a couple of years, but once the phone shows bootloop issue, it's done. There's no fix, no way to recover anything from your phone. LG denies that their phones have this issue. it's not widely reported, since people move on to a newer phone after 2 years, so very few people get to report the issue. LG V20 is the first phone that hasn't shown the issue even after 2 years. I'll have to give it 2 more years to say for sure that the issue is resolved. The phone does have removable battery and removeable SD card, which is great. The later LG V30, LG V40, LG V50 may not have this bootloop issue, but they don't have removable battery anymore (they do have removable SD card though). LG V20 also has USB-c port, which is a great feature to have, since all newer phones are moving to USB-C charging ports, which charge pretty fast (90% or so charge in less than 1 hour). I bought LG V20 for $100 in 2019 for a open box item (almost brand new), but now you can get these for < $70 (as of 2021). LG V20 is a 4G phone. LG V50 onwards are 5G phones.
    • LG V35 Thin Q: This phone doesn't have a replaceable battery, but is a nice upgrade from LG V20. LG V30, LG 35 and LG V40 are highly rated 4G phones. It costs about $100 buying used (like new) from amazon.
      • Here's a link (used like new selling for $100) => https://www.amazon.com/gp/product/B07D46BMYT
      • UPDATE May 15, 2022: Price of above phone has gone to $250 for used and $900 for new, so not worth buying anymore.
      • UPDATE 2024: These phones are not worth buying anymore, as world has moved to 5G.
    • UPDATE (May 2022): LG phone issue:  There are issues that can impact LG phones with little traction. One such issue was "LG IMS has stopped" issue that showed up on various models of LG phones, when an update was pushed by T-mobile. The fix below by Tmobile works for all LG phones, so try this method, and do not rely on other fix provided elsewhere on internet: 

 

 

Power bank:

These are one of those things that you absolutely need. Most laptops/phones have batteries soldered to them, so there's not an option to swap the battery with a spare one. Power banks generally have a storage capacity of certain Energy. Energy=Voltage*Current*time. This is in units of Watt-hr. However, in practice, Energy is quoted in current*time, ignoring the voltage altogether. That's OK as Voltage is usually 3.7V for most phones, and is assumed to be that level. So, the unit used is A-hr, or generally mAh (1000mA=1A). I would generally go with any power bank that has a capacity of at least 10,000mAh. Phone batteries are generally 3000mAh-5000mAh, so 10K mAh guarantees at least 2 full charges of phone. Even if the power bank is drained to half because it has been sitting idle for a couple of months, we are still guaranteed to get 1 full charge on a phone. If you plan to use a power bank for a laptop (only laptops with USB-C power interface), those power banks will need to have at least 25,000 mAh, so that they can survive 1 charge (~2-4 hrs)

Interfaces: Power banks have 2 interfaces. 1 interface is for charging which you connect to wall outlet, while other is for discharging which you connect to your phone or laptop. A lot of power banks have both interfaces as USB-A interface. USB-A interface supports smaller current only, so charging/discharging is slow. They provide a cable along with the power bank which have USB-A on one side on USB-C on other side so that you can charge your USB-C phones. Power banks which have inbuilt USB-C interface are more expensive, but better for faster charging/discharging. Those with USB-C interface use USB-C for both charging and discharging, which makes it very fast to charge. They laso provide additional USB-A ports (optional) for discharging, so that we can still use these with devices that have USB-A interface. Buy USB-C interface ones if you can find them close in price to USB-A ones.

 PRICE: Good Price to buy power bans is around $1/A-hr (with cables included) as of 2021. A lot of power banks are on ebay and amazon for cheap going for this price. However, not sure about longevity, so buy reputed brands when on sale.

 

 

Wall Chargers for phones:

These are wall chargers to charge your phones. Most phones have USB-C interface now, which can be used to charge phone faster. These are universal, meaning they can be used anyhwere in the world as they accept worldwide voltage from 100V-240V AC, and convert it to the needed DC voltage. Input side of the charger is the AC outlet voltage, while output side is usually a USB-A interface, USB-C interface, or a combination of the two. You should always look for wall chargers that have at least one output port as USB-C. That means these are going to be fast chargers as USB-C has ability to drive more or less current depending on the need of the phone battery.

Nowadays many laptops are charged via USB-C interface, and don't have traditional power outlet+adaptar any more. Such laptops can be charged via these wall chargers, if the wall charger has a USB-C output. That's one more reason to look for chargers with USB-C output port.

PRICE: Price for wall chargers depend on the wattage and whether or not it has USB-C output port. I would say wall chargers should have at least 25W of power (5V*2A for USB-A port to charge a phone, and assuming 2 such ports). Such chargers usually come for free with the phone. Most phones don't provide USB-C chargers. You should buy USB-C ones with wattage of at least 25W. Make sure they come with a USB-C cable (USB-C on both ends) as those cables runs expensive. These sell on ebay for $5 or so (without the USB-C cables). Good ones would be ones with 65W-100W of power rating, as they could charge a laptop too and are future proof. These go for around $10 for 65W charger to $25 for 100W charger (without the USB-C cables). I would say never pay more than $10 for any kind of USB-C charger. Price of these chargers go exponentially high as the wattage increases. 65W ones are more than enough for our needs, and that's also a sweet spot price wise. Few such links on ebay:

Link (65W): https://www.ebay.com/itm/363733309997 => 65W USB-C PD charger for $10 on sale (usual price is $20 for this, but similar ones sell for $12-$14)

Link (100W):  https://www.ebay.com/itm/334324277790 => 100W USB-C PD charger for $25

 

 

TV:

Prices of TV have fallen so much in the last couple of years, that you can now find 65 inch TV for $200 or so (as of 2020). TVs smaller than 40 inch regularly go on sale for < $100. TCL,

Black Friday 2020 had Target selling 65 inch 4K TV for $229. Fast forward 2021, and there were barely any > 65 inch TV for < $500.

2025: Fast forward to 2025, and there are 75 inch TV regularly for < $500, and even 85 inch TV for $600.

Below are the prices I would expect for TVs:

This is based on a 65 inch TV which has an area of ~1800 inch^2, while a 75 inch TV has an area of ~2400 inch^2. So, you get 33% more area, implying about 1/3rd higher price for a 75 inch TV compared to a 65 inch TV. For 85 inch TV, area is ~3500 inch^2 which is almost double the area of 65 inch TV. So, you should expect to pay double the price for 85 inch compared to 65 inch. However, there is a premium as you you go to larger size, as making larger LCD panels cost more per inch^2 than smaller LCD panels.

TV < 40 inch => price < $100

TV 40 inch to 65 inch => price < $200

TV 65 inch => price < $250

TV 70 inch => price < $300

TV 75 inch => price < $350

TV 85 inch => price < $500 (Cheapest 85 inch TV that I've seen as of 2025 is $600 at walmart, see in deals section below)

TVs larger than 75 inch are still very expensive to consider. A projector is a better option at that point. Look in the Projector section below.

 

TV Sticks:

These are small thumb drive sticks or boxes that allow your TV to become a smart TV (in case your TV isn't capable of running apps). I've personally never realized the need for these, as most of the TV nowadays have all the smartness they need. However, sometimes the TV may only allow only certain apps to be downloaded, because your TV may be running "Google App store" and those apps aren't there. In this case, may be Amazon Fire stick might allow you to run that app. Or Roku stick may allow you to stream something that isn't allowed on other TV sticks. Many times you need these for your projectors, as cheap projectors don't have the "smartness", and plugging in these TV sticks does the trick.

These TV sticks are like mini computer or a end point router. They have a processor and programs running on it, that allow to stream data from internet. What they can or cannot stream depends on the app running on it. The only reason you get them is because they are so cheap. You want to keep one just in case. There are 4K versions available as of 2024 that regularly go on sale. You don't want to pay > $25 for any of these 4K sticks. You can make one yourself by buying a "Raspberry Pi" with a fast enough processor. However that will cost you > $25. So, just use theirs. The non 4K versions should  sell for < $10 or be free.

Amazon Fire Stick is the first choice for TV stick. Then comes Roku, though I don't see a reason to buy Roku over Amazon Firestick. Many apps on Roku require subscription, while on Amazon fire stick, they are free. Even on google TV, they aren't free. I'm getting IP TV service, and had to get "Amazon Firestick" as the "IPTV Smarters Pro" was available for free download only on Amazon Firestick.

Deals:

 

 

Projector:

Projectors are best when you have a wall big enough with height x width > 5ft X 7 ft. Usually you can find at least 1 wall with those dimensions. At that point, the diagonal is about 8 ft, which is equivalent to 96 inch TV. Any TV > 75 inch diagonal costs close to $1K (as of 2022), but a nice projector could be had for under $500. Projector bulbs are the weakest link in making a projector affordable. A projector bulb lasts 3-4 years, and is very expensive (>$100) to replace. However, if your projector usage is very low (which usually is after you had a projector for a couple of years), then your bulb will last longer. They rate the bulb for 3000-4000 hrs. So, if you watch 1 movie everyday, then your bulb will last 3-4 years. More practical use is 3-4 hrs/week, in which case, yor bulb should last 10 years. It's probably better to buy a new projector, then spend money on a new bulb. Don't spend money on extra bulb when buying a projector (all projectors come with a bulb). The extra bulb will just sit idle for a long time, and may have a much shorter life when it's time to use.

Below are few items you need for a projector:

  • 4K projector: Even a 1080P projector would serve fine. There are tons of projectors out there, and hard to decide. I would suggest go with any entryline 1080P projector from Epson.
    • Epson PowerLite 2045 Full HD: This is a very good 1080P projector. I bought it for about $360 ($375 - 5% in Extrabucks) way back in 2018, when ebay used to have good deals. Good old times !! It's 4 years, and still runs great. https://www.ebay.com/itm/31206136056
  • Projector Screen: It's a big screen made of fabric on which your projector displays the picture, as picture displayed on the wall doesn't look good (depends on the wall though). People buy really fancy motorized screens, what you need is just a white thick sheet. That way you can fold and keep it when not in use. The big flat screns are not only expensive but also permanent attachment to wall. There's no visible difference in display quality for fabric screen vs solid expensive screens. I
    • Excelvan 150 inch Projector screen: I bought this on amazon, and it's as good display as you can get. It's made of PVC or something, but much thicker and no crease on the screen. It cost me $20. https://www.amazon.com/gp/product/B0719SVHDF
  • Projector holder: A table or something to keep your projector on. I had always kept my projector on a table on floor, which served fine. I was always scared of making a hole in the roof to attach the projector and NOT knowing what I'm doing. Recently, I switched to the below projector holder which attaches to a wall, so is very easy as a DIY:
    • Wali Entertainment Shelve: Very easy to attach to a wall. Make sure you have a stud finder, so that you nail this thing on to the stud and not to the drywall. It's price is ~$20. I bought it used for $15. You can buy 2 of these, if you want to have more flexibility on different shelves to put the projector on: https://www.amazon.com/gp/product/B00UB062ZQ

 

TV Sticks: You may need to buy a TV stick to stream shows/movies on your projector (if your projector isn't smart). IT costs < $25. See above section on TV.

 

 

Wireless in ear head phones (aka earpods):

These are the wireless headphones. Instead of going over your head, they go in your ears. Most people call them Earpods, even though that name seems to be reserved for Apple branded ones. Almost all other companies refer to them as "wireless in ear head phones". They aren't worth anything > $30, since you can get good quality headphones for < $30.

A. JLab: JLab isa relatively new audio company founded in 2005. It started by making in ear head phones, but since then has branched into making other audio products. They make economical audio products, and made it in top 5 audio brands in USA. They are based in California. They were purchased by Noritsu, a big japanese company in 2021. They are growing somewhat reputed company making great products at reasonable prices. However, some reviews consider them at the bottom of the pile, with SkullCandy being the worst ones. However, reviews for their headphones are usually great. Their regular price is around $20. If you find them on sale or clearance for < $10, grab them as they usually don't go for much below their regular price. Below are some of their headphones:

1. JLab - GO Air POP True Wireless In-Ear Headphones:

These sell at bestbuy for $20. That's the regular price !! They have 4.5 star rating there, and are the most value that you can get on these in ear headphones.

Link: https://www.bestbuy.com/site/jlab-go-air-pop-true-wireless-in-ear-headphones-black/6472667.p?skuId=6472667

Also at walgreens for $19. Link: https://www.walgreens.com/store/c/jlab-audio-go-air-pop-true-wireless-earbuds/ID=300421313-product

 

B. JBL: JBL is a audio company known for making great audio products. They are a subsidiary of Harman, which is the parent company that has other brands under it too. Harman is a big company employing 30K people in USA, Europe and Asia. In March 2017, HARMAN became a wholly-owned subsidiary of Samsung Electronics and is mentioned on harman.com site as "Harman - A Samsung company". JBL is a very old company (around 80 years) and much bigger than JLab, it's a great brand that makes great reliable economical products (though expensive than JLab). JBL is considered reputed company, and though you pay a little more, but they are considered amongst the top ones for cheap earbuds. I've used JBL. They come in a very nicely packed box, and look and sound amazing. They are the best amongst all the other brands I listed. Some of their great products are:

I. JBL Reflect Flow True Wireless Sports Headphones:

These are usually $60-$70, but go on sale for $30 or so. These are the best according to some reviews, even better sounding than $200 ones from expensive brands. Available in 3 colors. 2 colors show under 1 link, while the black color has a different link, just absurd.

Deal: https://slickdeals.net/f/15691546-jbl-reflect-flow-waterproof-true-wireless-bluetooth-sport-earbuds-teal-green-30-6-sd-casback-free-shipping?src=frontpage

Direct link for green/teal: https://www.ebay.com/itm/393986583705

Direct link for black: https://www.ebay.com/itm/JBL-Reflect-Flow-Waterproof-True-Wireless-Bluetooth-Sport-Earbuds-Black-/393798263125

II. JBL Live 300TWS True Wireless Bluetooth In-ear Headphones:

This is also very similar to JBL Reflect. Somepeople claim that it has better sound quality than JBL Reflect. One advantage this has is that it USB-C port for charging, compared to USB mini (type A) that JBL Reflect has. However, JBL Reflect is the newer one. Both sell for about the same price though, when not on sale. On sale, 300TWS goes for about $38.

 Link: https://www.ebay.com/itm/203907214403

Deal: https://slickdeals.net/f/15685378-jbl-live-300-premium-true-wireless-earbuds-black-or-blue-38-free-shipping-w-prime

C. SkullCandy:

People say they are at the bottom of the pile. They are the cheapest ones, but quality is also low. However, reviews seem good

I. Sesh wireless earbuds:

These are also decent and go for $15 on woot quite often.

Link: https://slickdeals.net/f/15720454-skullcandy-sesh-true-wireless-bluetooth-earbuds-13-99-free-shipping-for-prime-members-13-99?src=frontpage

II. Jib 2 wireless earbuds:

These sell for $30 new on amazon, but refurbished ones may be had for $10 or so. Not bad for the price.

Link: https://slickdeals.net/f/15799438-skullcandy-jib-true-xt2-wireless-in-ear-earbuds-refurb-black-10-85-6-sd-cashback-free-s-h

 

D. TOZO:

This looks like a cheap brand and I found it by accident on amazon. All their earbuds are highly rated on amazon. They all sell for $20-$30 when on sale.

I. T6, T10 and T12 True wireless earbuds:

T6 are highly rated on amazon (200K+ reviews)). I bought these for $22.50+tax, and they regularly go on sale for close to that. There are other versions as  T10, T12. According to a reviewer on reddit, "T12 is best sound-wise, T6 is best for calls, T10 is the cheapest, the differences between them aren't big". They all sell for $20-$30, so go with what suits you. T10 has even more reviews at 300K+, and is highly rated too, but looks like T6 is the newer model, so should perform better.

Link for T6: https://www.amazon.com/TOZO-T6-Bluetooth-Headphones-Waterproof/dp/B07RGZ5NKS => $22.50 on sale (regular price is $60, but never saw them selling for over $30)

Link for T10: https://www.amazon.com/TOZO-Bluetooth-Wireless-Headphones-Waterproof/dp/B07J2Z5DBM => $22 on sale (regular price is $26)

Link for T12: https://www.amazon.com/TOZO-Bluetooth-Headphones-Intelligence-Waterproof/dp/B085DL3KMR => $25 on sale (regular price is $30)

Don't forget to get the $2.99 "3 year protection plan" provided by Asurion LLC on amazon (there's a button to add the protection plan on right side of screen, just below "add to cart"). This will make sure you have the device protected for 3 years for any mishaps. I don't know if they will pay or not, as I've never used them before. Reviews are mixed on that.

 

CONCLUSION: Headphones go for $10 or so. Wired in ear headphones go for free (airlines, audio tours, etc give them for free). Wirless in ear headphones may cost some money due to it's wireless circuitry. In any case, I wouldn't expect wireless earbuds headphones to cost anything > $10 to manufacture. Considering that, I would say go with JBL as they are reputed. They cost about $30 or so, but you don't get reupted brands for less than that. I had no issues with Tozo, JLab and SkullCandy. However, I haven't kep any of these long enough to make a comment on their longevity. The biggest issue with cheap brands is that they die too soon.

 

 

Smart Watch:

Watches became useless with arrival of phones, saving you moneyon watches. Fast forward from 2000 to 2020, and watches are back and ridiculously expensive, and the usage of which was questionable when they came out, and now they are the one of the big fashion accessories. They aren't worth anything > $50, as they practically have no known use except fashion.  Anyway, here are your most economical smart watches:

1. Popglory Smartwatch:

These sell on amazon for $30, but usually go on sale for $25. They have 4 star reviews. Good thing is that they have all measurement devices inbuilt in watch which are only seen in expensive watches (as measuring blood pressure, oxygen level, pulse rate, etc). They are regularly in top 10 best sellers in smart watch. You will need to download their app "heroband III" in order for the watch to work. there are many apps with similar name "heroband 3", those won't work with this watch. You may add a "3 yr protection plan" for only $3 when buying from amazon, so defintely do that, as these things get in harm's way easily. This only comes in 1.4 inch size.

Link for 1.4 inch watch: https://www.amazon.com/gp/product/B08DXS7VCK

2. Donerton Smart Watch:

These sell for $38 for 1.4 inch watch, and $42 for 1.7 inch watch on amazon. However they go on sale or have coupons frequently, bringing the prices down to $30 for 1.4 inch and $35 for 1.7 inch. They have 4 star revies, and look similar to PopGlory ones above. They use the same "heroband III" app to work. They have "3 yr protection plan" for $5 for the 1.4 inch watch. Weird that they don't provide protection plan for 1.7 inch watches. They are regularly in top 10 best sellers in smart watch (along with Popglory). Not sure why the premium of $5 on these watches compared to popglory for same size watch with similar functionality.

Link 1.7 inch watch: https://www.amazon.com/gp/product/B09STMM8F5

Link 1.4 inch watch: https://www.amazon.com/gp/product/B08DTNHDYJ

 

 

LED bulbs:

These LED bulbs have virtually replaced traditional as well as CFL bulbs. LED bulbs are even more efficient than CFL bulbs. These now come in various shapes, sizes and wattage. They also come in dimmable version now. You can find equivalent of 65W and 90W bulbs for a dollar or less. They usually go on clearance at HomeDepot and Lowes for 75% off multiple times a year, which results in a price of $1 or less. Each of this LED bulb uses energy of about 10W or so. Assuming the bulbs are ON 5 hours a day, 365 days a year, they will consume about 20KWhr. since 1 Kwhr costs about 10 cents, They will cost about $2/year in electricity cost. Assuming you have 20 such bulbs which are ON for about 5 hours/day, you will spend about $40/year. These bulbs themselves will cost about $10-$20 assuming you buy 20-50 of them. These will last at least 5 years, so effective cost per year is about $4 or so for replacing these 20 bulbs. You can't buy any bulb, incandescent or CFL, anywhere which cost anywhere close to these (since filament or CFL bulbs last at most a year and cost atleast $5 for 20 bulbs).

LED bulb light type: LED bulbs which have white light (NOT the yellowish light) are my preferred ones, as they are so much better lighting and easier on eyes when reading, etc.

  • Warm White or Warm Light (3000K): These are the ones that give yellow light (similar to what incandescent bulbs used to give, i.e similar to what's emitted at 3000K temperature)
  • Day Light or Cool Light(5000K): These are the ones that you should buy. The light is white (similar to what tubelights give, i.e similar to what's emitted at 5000K temperature). Note: it's called cool light, even though the temperature is higher.
  • As of 2024, we now have LED bulbs which have all 2 or 3 lights in the same bulb. You just have to flip a switch on the side to select the light you want (Warm light or cool light). These bulbs cost just a bit more than regular ones.

LED bulb Power: The power of the bulb decides the amount of light or intensity of light.

  • 40W/50W LED replacement (consumes 6W-7W) => These are low wattage. Brightness is also low at 500 lumens.Not suitable for big areas, OK for closets, etc.
  • 60W/65W LED replacement (consumes 8W-9W)  => These are the most common ones, regular size bulbs. These are the ones mostly on discount, and available everywhere. Brightness is 600 lumens.
  • 75W/90 W LED replacement (consumes 10W-13W) => 90W is most bright, is bigger size, but is very suitable for ceilings, and places where you read, work, etc. Brightness is really high at 900 lumens. My 90W bulbs show current=137mA @120V (RMS), so Pwr=V*I=0.137*120=16W. Not sure why the pack says 13W. May be current is not RMS current. There are 100W LED bulbs also which are more expensive. These 90W ones will suffice for everything. There are  > 100W equivalent which may be suitable for very large spaces.
  • > 100W LED replacement => These bulbs used to be very expensive but as of 2025, you can get 100W to 300W equiv LED bulbs for $2-$7 apiece, and almost the same size as 90W bulbs, which is insane. Some of these bulbs are rated for >20 yr lifetime, and also come with a warranty (if you buy from reputable brand as Sunco). I would stick with brands offering warranty, as these bulbs are expensive.

 PRICE: Good Price to buy LED bulbs is around $0.50/bulb for 65W equivalent, and $1/bulb for 90W equivalent. 90W equivalent are rare to find, so grab them fast when they go on clearance. 200W bulbs can be had for $5/bulb with coupons/discounts.

 

 

Tubelights:

In any home or apartment, you will find at least few tubelights (usually in closet, garage, laundry rooms, etc). These Tubelights are either made for regular fluorescent Tubelights or LED Tubelights. However, unlike bulb sockets where you can put either fluorescent bulbs or LED bulbs as they are interchangeable in the same socket, you can't do the same thing with Tubelights. Tubelight socket will need some changes if you want to change your existing fluorescent tubelights with LED ones or vice versa. Fluorescent tubelights have "Ballast" that regulate the current flowing thru the tubelight, which in turn produce light by exciting mercury vapor. On the other hand, LED tubelights don't need this ballast, as they work like regular LED bulbs. There are newer LED tubelights that can work with Ballast too, but you have to spend more money and carefully choose the LED ones that can go in your Tubelight socket. Best to stick with whatever you had before, as it's not worth the swap with a different one.

The Tubelights have writing as "F32T8" which means it's a 32W tubelight with T8 or thin 1 inch diameter. Another version that is also very popular is "F40T12" which is a 40W tubelight with T12 or thicker 1.5 inch diameter. These thicker tubelights are less energy efficient and even though they are 40W, they give same light as the 32W thinner ones. So, buy F32T8 if you are using a fluorescent tubelight. Both T8 and T12 pins are exactly the same, so they can be interchanged. The length of tubelight is usually 48 inchs (from pin to pin). You have to make sure that tubelights are 2 pin (if your existing lights are 2 pins on each side, more common) or 1 pin (if your existing lights are 1 pin on each side)

Prices:

Fluorescent tubelight => Pack of 2 for ~$5 on sale

LED tubelight => pack of 2 will cost > $10.

 

 

Batteries:

There are AA (larger diameter, thicker batteries) and AAA (smaller diameter, thinner batteries) batteries which are most commonly used in devices. There are 2 kinds of batteries => Rechargeable and non-rechargeable. Rechargeable batteries cost more than non rechargeable batteries.

Re-Chargeable batteries:

These cost about $1 to $1.50 per battery. You need to buy a charger too, which will cost $5 or so. Eneloop batteries are the best.

Non Rechargeable batteries:

These cost about about 10 cents per battery.Their regular prices are lot higher, but you can find them for 5 to 10 cents during sale.Some folks think that rechargeable batteries are cheaper in long run, so why bother with non rechargeable batteries. This may be true in some of the items, that drain a lot of battery. But in most of the cases, non rechargeable batteries are cheaper. Rechargeable batteries die in about 5 years. So, in order to cost the same as Non rechargeable batteries, you have to completely use the battery once every 3 months. If your batteries aren't getting drained that fast, it's better to stick to non rechargeable batteries. The only places I put rechargeable batteries are kids toys with motors, portable lights, drones, etc. Everything else, just buy non rechargeable at these sale price, and you would be better off.

These usually come on sale at bestbuy (pack of 48 for $6).

These also come on sale at OfficeDepot+OfficeMax (They are one company now) for free after rewards (you get back rewards for the price you paid for battery). Rewards expire in 3 months, and you get them immediately after pickup. You can buy almost anything with rewards, except gift cards. Also rewards can't be rolled, i.e if you use your older reward points to buy batteries which are free after rewards, your reward amount will be reduced by the older reward points you used. As an example, if you buy batteries and pay for it completely using reward points, you will earn nothing in new reward points (no 100% rewards back). Since everything is expensive at OfficeDepot + OfficeMax, you can always buy postage stamps with these rewards (if you can't find anything else for a reasonable price). However, don't amass too much in rewards, else you will be stuck with stamps to pass on to your grandkids.

PRICE: Good Price to buy Batteries is around $0.10/battery for non rechargeable ones and $1 for rechargeable ones (both for AA batteries). AAA batteries should go for lower price since they have less than half the capacity of AA ones, but unfortunately they sell for only a little bit cheaper than the AA ones.

 

Bigger LifePO4 Batteries: We now have LiFePO4 batteries which are same size as your car batteries. These are useful for charging your devices as laptops, small electronics, or can be used in camps, etc to power lights, fans. They can be charged by solar panels, so these batteries are bought together with solar panels, which themselves are getting pretty cheap.

These batteries go for < $0.10/KW-hr of energy stored (as of 2025). In contrast AA/AAA batteries go for $0.50/KW-hr. So, where possible go with these big batteries, as these are 5X cheaper, and getting cheaper every year. They also run for > 10 yrs. Prices are falling fast in 2025, so if you wait till the end of yr, you may start getting these for $70-$80 per KWhr.

LiFePO4 battery can be bought from amazon, ebay, aliexpress for < $100 for 1KWhr. Eco-Worthy is a reputed brand for both batteries and Solar panels. Buying from aliexpress gets you 15%-20% Cashback, so that's extra savings. Below are few deals:

 

 

 

Solar Panels:

Since Solar panels are getting so cheap, I decided to include these. They are also getting portable, where you can carry it in your car. Renogy brand from Aliexpress has tons of sale,  Few deals below:

 

 

 

3D Printers:

3Dprinters have been in press and availed as the next big thing for the last 5 years. However they never took off in a big way probably because there are no big and fashionable electronics companies in it. I've never owned a 3D printer, but I would like to buy one someday when the prices go to < $100. They can be used to make plastic parts for things that break in your appliances, eletronics, etc that make that device unusable. Of course making these replacement parts using 3D printers is neither cheap nor easy. However, it may serve as good learning experience. 3D printers do require a lot of tinkering to get it working right. Expensive ones come ready out of the box. These are some popular 3D printers (taken from the web, I've no personal experience):

  • Creality: Bet for a beginner to learn and make mistakes. Ender 3 is low end and regularly sells for $99 at microcenter. Highly recommended on slickdeals
  • Prussa: Used in a lot of companies. It allows you to minimize your early mistakes, so better than Creality
  • Ultimaker: Best printer, and is ready out of the box (no diy abilities or tinkering needed) but it's expensive

These are some of the recent deals. Read thru comments as they have a lot of valuable feedback on what works, info for beginners, etc

PRICE: Good price, depending on the brand is under $100. It's hard to justify the investment for anything over that.

 

 

Wires/Cable, Outlets, Extension cords, etc:

I'm talking about wires that you need to run around your house. You will need to buy these if you are going to be running wiring outside or inside your house. Electricians are very expensive, so doing it yourself is not only easy on pocket, but also really simple. An ex of when you might need to run wires around your house is when you are installing a mini split AC (if you need a dedicated outlet or disconnect box). Look in "Power Transmission" section under "Education" for more in depth understanding of the wires. Our price target should be 50 cents/foot for the wires running inside the house. These are called "Romex" wires. Not sure, why these wires are more expensive than similar rated "extension cord" wires. Maybe they have better insulation, and better built ground wire.

There are also various "outlet wall adaptar" that have 6 outlets or so that plug into the wall. These go for $3 or so when on sale (though I was told that Dollar stores carry these for a dollar).

Extension cords are thick wires that you run when you have an external equipment that can't reach an outlet. These are somewhat inexpensive costing $20 or so, for 100 ft wire. Our price target should be < 20 cents/foot. These come in both outdoor/indoor variety.

 

 

Solar Panels:

Solar Panels have gotten very cheap as of 2024. You may get 200W Solar panels for $50 or so very easily on ebay. Some defective ones may be gotten for much less than this.

 

 

MiniSplit / AC:

Minisplits have become very popular as they are more efficient than regular central AC, and on top of that they are DIY. So, you can install 2 or 3 1 TON minisplit for a total cost of $2K for your whole house. Compare that to the price of regular AC which will cost you $10K t get istalled. See in "Minisplit DIY" section for deals and on how to install one.  

 

 

Sticky Deals:

 

OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries after rewards  => every few months

This deal is there almost every month. Lately, as of 2023, it's more and more uncommon. Comes every few months now. Limit is 2. Better to buy 2 sets of 24 batteries (AA or AAA depending on need, you can mix and match). They always have offers where you get a free item or a free Giftcard if you spend $50, $75, $100 etc. Try to take advantage of these deals, while you are ordering the batteries. Usually 2 24pack batteries cost just under $50, so add any filler item from clearance section, and you can get yourself a better deal. Everything is overpriced at OD, but you can get clearance items for cheap. If you can't find anything at decent price in store/online in clearance section, use rewards to buy stamps. Below are the deals:

 

 

TV deals   => every BF/Christmas time

This deal is there almost every year. Prices for TVs have started coming down as of 2024, so might be a good time to start shoopping for TV.

Lately, as of 2023, it's more and more uncommon. Comes every few months now. Limit is 2. Better to buy 2 sets of 24 batteries (AA or AAA depending on need, you can mix and match). They always have offers where you get a free item or a free Giftcard if you spend $50, $75, $100 etc. Try to take advantage of these deals, while you are ordering the batteries. Usually 2 24pack batteries cost just under $50, so add any filler item from clearance section, and you can get yourself a better deal. Everything is overpriced at OD, but you can get clearance items for cheap. If you can't find anything at decent price in store/online in clearance section, use rewards to buy stamps. Below are the deals:

 

 

 

 

DEALS:

 

2025:

 

 

 

11/14/2025: 98 inch TCL TV for $1000 at Walmart

Seems to be decent price so far for 100 inch TV. It's part of their Black Friday sale, which is available early. More deals also available in link below.

98 inch TCL TV => https://slickdeals.net/f/18737275-98-tcl-98q51cg-qled-4k-google-tv-998-more?src=frontpage

NOTE: 98 inch TV may not fit in trunk. My Sienna minivan was able to fit 86 inch TV in trunk. Anything larger wouldn't fit in trunk, may need to go on roof of car. Buy straps to tie it to car.

 

 

04/29/2025: Walmart TV deals - 86 inch LG TV for $600 => (expiry => until they sell out everywhere)

Seems to be the lowest price so far for 85 inch TV. Lots of other TV also on sale. LG 85 inch will sell out fast (few are only available for pickup), as that's the best deal of all TV deals below.

86 inch LG TV for $600 => https://slickdeals.net/f/18282970-select-walmart-stores-86-lg-uq7070-series-4k-uhd-120hz-smart-webos-tv-599-free-store-pickup-pricing-availability-may-vary

85 inch Samsung TV for $600 => https://slickdeals.net/f/18282304-85-samsung-class-du7200b-crystal-uhd-4k-smart-tv-2024-599-free-shipping

75 inch LG TV for $400 => https://slickdeals.net/f/18282496-lg-75-class-4k-uhd-2160p-webos-smart-tv-75uq7070zud-399-at-walmart

75 inch Samsung TV for $400  => https://slickdeals.net/f/18281647-75-samsung-class-du7200b-crystal-uhd-4k-smart-tv-un75du7200bxza-399-free-shipping

70 inch LG TV for $350 => https://slickdeals.net/f/18284815-70-lg-uq7070-series-4k-uhd-led-smart-tv-349-free-shipping

70 inch Samsung TV for $400  => https://slickdeals.net/f/18283933-samsung-70-class-du7200b-4k-smart-tv-at-walmart-399

There are few other TV deals too, though all inferior to these . Be sure to check them all out on walmart website as some 40 to 60 inch TV also have good prices.

 

 

 

2024:

 

 

08/19/2024: Apple Ipad (9th gen, 2021 model) for $200 (various retailers), 10th gen (2022 model) for $250 on BF => (expiry => until they sell out everywhere)

Seems to be the lowest price for this mode, was the last model with power adaptar. It has Apple's Lightning cable port instead of USB-C, so you will have to carry that extra cable around (those lightning cables are dirt cheap now). It also supports 1st gen Apple pencil, which may be bought for discount too.

Available at multiple retailers as of 08/19 => Target, BestBuy, Amazon. (more will follow soon). Prices will come down during BF/Christmas, so buy it from from Costco (buy in store to save $5 on shipping) which has 90 day return window. BestBuy/Target has only 14 days while amazon has 30 days. 10th gen iPad is selling for $280 at Target /Microcenter, so prices will definitely come down for both 9th and 10th gen in next few months.

Target => https://slickdeals.net/f/17696895-64gb-apple-ipad-10-2-wi-fi-tablet-9th-gen-2021-space-grey-or-silver-200-free-shipping

Amazon, BestBuy, Costco => https://slickdeals.net/f/17700411-64gb-apple-ipad-10-2-wi-fi-tablet-9th-gen-2021-space-grey-or-silver-199-free-shipping

UPDATE 11/19/2024 => Ipad 10.9 inch (2022 model) is also available on sale for $250, which might be a better deal than the above deal. Previous deal is still available and goes in and out of promotion, but multiple retailers have it.

Ipad 10.9 inch is available at Costco and Amazon:

Amazon => https://slickdeals.net/f/17981235-64gb-apple-10-9-ipad-wi-fi-tablet-2022-10th-gen-silver-250-free-shipping

Costco => https://slickdeals.net/f/17903091-costco-members-64gb-apple-10-9-ipad-wi-fi-tablet-10th-gen-blue-or-silver-250-available-in-store-limited-locations

 

 

 

 

2023:

 

 

10/10/2023: Dell Inspiron Laptop for $308 (possibly $208 with 2 Amex cards): 

A very solid laptop. Worth it with Amex offers of $50 with $100+ purchase. If you have 2 cards, use both cards and split the amount, bringing total to about $210 + tax. Usually, you also get 1% cashback from ebates, SB, topcashback, etc. Also look in comments on how to upgrade memory (it has 2 dimm slots, so just buy an extra 8gb memory module).

https://slickdeals.net/f/16992328-dell-inspiron-15-laptop-15-6-1080p-touch-amd-ryzen-5-7530u-8gb-ram-512gb-ssd-308-70-free-shipping

 

 

07/01/2023: SSD and DDR Memory on sale at multiple retailers

SSD and DDR prices keep falling with Top rated 32GBx2 (64GB) DDR4 modules for $100 and 2 TB M.2 SSD for $100. Replace these in any mid range laptop and you will get a beast.

SSD M.2 PCIe Gen3/Gen4:

DDR4 SO-DIMM Laptop Memory:

 

 

04/27/2023: Amazon - 1 TB PNY 2.5 inch SSD for $38

1 TB 2.5 inch SSD:

2 TB 2.5 inch SSD: = $132-$15(coupon)=$117

 

Good price for highly rated SSD as a replacement for HDD (has SATA interface and same size as 2.5 inch HDD). Prices may keep falling as there's a glut of Memory on market. But 1TB SSD for < $50 is a very good price considering 1 TB HDD were going for this price just a year back. So, SSD prices have fallen to same level as HDD from couple of years back, so no reason not to swap that old HDD with SSD.

 

 

02/05/2023: Amazon - 1 TB Crucial MX500 SSD for $62 $52 (as of 02/18/23), 2TB for $117 $103 (as of 03/09/23)

 

1 TB = $62, Link: https://slickdeals.net/f/16426939-1tb-crucial-mx500-2-5-3d-nand-internal-solid-state-drive-ssd-61-99-f-s-amazon?src=pdw

UPDATED: 02/18/23: 1 TB selling for $52 (At BestBuy, B&H Photo and Amazon) => https://slickdeals.net/f/16459171-crucial-1tb-mx500-2-5-internal-sata-ssd-51-99-free-shipping-b-h-photo

 

2 TB = $132-$15(coupon)=$117

UPDATED: 03/09/23: 2 TB selling for $103 => https://slickdeals.net/f/16497436-2tb-crucial-mx500-tlc-3d-nand-2-5-solid-state-drive-ssd-103-free-shipping

UPDATED: 02/18/23: 2 TB selling for $120 => https://slickdeals.net/f/16452505-2tb-crucial-mx500-tlc-3d-nand-2-5-solid-state-drive-ssd-119-99-f-s-amazon?src=frontpage

Good price for highly rated SSD as a replacement for HDD (has SATA interface and same size as 2.5 inch HDD). Prices may keep falling as there's a glut of Memory on market. But 1TB SSD for < $50 is a very good price considering 1 TB HDD were going for this price just a year back.

 

 

02/01/2023: Free Hard Disk Monitoring Software for download - expires Feb 28, 2023

https://slickdeals.net/f/16416748-hard-disk-sentinel-standard-lifetime-giveaway

Direct Link: https://giveaway.tickcoupon.com/hard-disk-sentinel-standard-license-free/

From the reviews, it seems good to grab one. You can also install the copy on other computers if you copy the downloaded file to other computers. No emails, login, account required to buy or use.

 

 

01/19/2023: Dell - 27 inch 1080P gaming monitor for $200 + Free $125 Dell Promo GC - expiry unknown

https://slickdeals.net/f/16391362-27-dell-g2723hn-fhd-165hz-ips-freesync-gaming-monitor-125-dell-egift-card-200-free-shipping

The deal has been coming on and off for a while now. It's the cheapest I've ever seen for a 27 inch gaming monitor. However $125 is in Dell GC, so you will have to find something to use it on in next 3 months.

 

 

01/07/2023: Lowes (Select stores only) - 65W/90W LED bulbs for ~$0.20 to $0.30 per bulb => on clearance

https://slickdeals.net/f/16364917-ymmv-ge-led-flood-90-watt-eq-led-par38-daylight-flood-light-bulb-12-pack-3-17-or-65-watt-eq-3-17-or-dimmable-5-98-lowes-ymmv

It's the cheapest I've ever seen for a 65W and 90W bulb. These will get cleared out fast, so hurry up if it's in your local store. This is GE bub, so reputed brand. Both 65W and 90W bulbs re great steal !!

 

 

2022:

 

 

12/05/2022: Home Depot - AA/AAA batteries for 30 cents each:

https://slickdeals.net/f/16200346-energizer-max-aa-batteries-36-pack-14-87-41-per-battery-aaa-30-pack-14-87-50-per-battery-ymmv-home-depot-w-free-shipping-or-pickup-now-active-online?src=frontpage

4 sets of 36 AA batteries for $15*4-$10=$50. So, price= $0.30/AA_battery. Not cheap, but this is the best at this time. AAA batteries are little more expensive.

 

 

11/01/2022: Amazon - pack of 24 Rechargeable AA batteries for $11:

https://slickdeals.net/f/16142929-amazon-basics-24-pack-aa-rechargeable-batteries-recharge-up-to-400x-high-capacity-2400-mah-pre-charged-10-77-10-75

This is the cheapest for any rechargeable battery for $0.40 per piece. This is Amazon Basics brand, which has reputable quality. Won't last long. Think later !!

 

 

09/24/2022: Ebay - 17.3 inch HP laptop for $335 (refurbished):

This deal is for 17.3 inch refurbished laptop for $335 with 15% off coupon.  Comes with 2 yr comprehensive warranty by Allstate.

https://slickdeals.net/f/16054447-hp-17-cn1053cl-17-3-laptop-ips-anti-glare-intel-i5-1155g7-12gb-ddr4-1tb-hdd-iris-x-graphics-windows-10-certified-refurbished-two-year-warranty-335-74-with-coupon-free-shipping

Conclusion: Similar HP laptops may be had for $300 or so. It's very nicely made, and HDD can easily be upgraded to SSD (look in slickdeals comments). This is good price.

 

 

09/21/2022: Hisense 65 inch TV for $250 at Costco => expires 10/23/2022

Finally 65 inch TV for $250. It comes with 3 yr warranty. You do need Costco membership though. Look in Shopping section on how to get Costco membership for cheap.

https://slickdeals.net/f/16048606-upcoming-9-28-offer-costco-members-65-hisense-class-a6-series-4k-smart-hdtv-250-after-100-rebate-free-s-h?src=frontpage

 

 

07/10/2022: Energizer indoor wifi security camera for $17 at walmart: 

Decent price for a security camera. It's indoor and no battery (so need to have power plug close by). You may put a SD memory card in it, and get recordings saved whenever there's motion. Hard to find any security cam for this price.

https://slickdeals.net/f/15863998-energizer-smart-wifi-camera-16-88?src=frontpage

 

 

07/09/2022: Dell G15 Gaming Laptop for $588: 

A very solid laptop. Usually, you also get 10% cashback from topcashback, but right now it's only 4%. Also look in comments on how to upgrade hard drive and memory.

https://slickdeals.net/f/15894457-dell-g15-gaming-laptop-15-6-120hz-i5-11260h-8gb-ddr4-256gb-ssd-rtx-3050-588-free-shipping

 

 

07/01/2022: HP 17.3 inch refurbished Laptop on ebay for $350 with 2 year warranty: 

A very good laptop for the price. Also look in comments on how to upgrade hard drive and memory.

https://slickdeals.net/f/15879970-hp-laptop-refurb-i5-1155g7-17-3-fhd-ips-12gb-ram-1tb-hdd-2-yr-warranty-350-free-shipping

 

 

06/24/2022: Walmart -25 ft Southwire indoor copper wire for $11: 

This deal is for 25 ft indoor electrical wiring, and has 3 wires - hot, neutral and ground. This wire is the one that goes around your house inside the walls. This can be used, if you need to run any more wiring thru your attic to some other place in house. Typical example is to run this wire for your newly installed mini split AC or for adding extra outlet in wall.

https://slickdeals.net/f/15864682-25-southwire-romex-simpull-14-2-nm-b-indoor-electrical-copper-wire-white-10-75

 

 

05/14/2022: Walmart - 65 inch 4K Series 4 TCL TV for $400:

This deal is for Series 4 TV. Comments state that Series 6 is lot better than Series 4, but Series 6 is more expensive too. Similar TCL TV sold in 2020 Black Friday for $230 (see 2020 BF deals section). This is an OK price for 65 inch TV considering prices have gone up a lot in 2021 and 2022.

 https://slickdeals.net/f/15752971-65-tcl-65s431-4-series-4k-uhd-hdr-roku-smart-tv-398-free-store-pickup?src=frontpage

 

 

05/07/2022: Walmart - 17.3 inch HP laptop for $500 (new) or $379 (refurbished):

This deal is for 17.3 inch new laptop for $500:

 https://slickdeals.net/f/15770965-hp-laptop-intel-core-i5-1135g7-17-3-1080p-ips-300-nits-8gb-ddr4-512gb-ssd-iris-xe-win-11-499-free-shipping-walmart

Walmart link: https://www.walmart.com/ip/HP-17-3-FHD-Intel-Core-i5-1135G7-8GB-RAM-512GB-SSD-Natural-Silver-Windows-11-Home-17-by4061nr/274981158

Another deal is for refurbished version of this laptop sold by walmart. This looks to be out of stock most of the time (3rd party sellers sell it for more than the price of new one).

https://slickdeals.net/f/15750811-17-3-hp-laptop-refurb-i5-1135g7-1920x1080-ips-8gb-ram-512gb-ssd-379-free-shipping

Walmart link: https://www.walmart.com/ip/seort/353306478

Conclusion: I've used this laptop. It's very nicely made, and RAM can easily be upgraded (look in slickdeals comments). This is good price. It has come on sale at $500 multiple times in the past couple of months. I haven't seen refurbished one for $379 though.

 

 

05/01/2022: Home Depot - 6 outlet wall adaptar for $3:

https://slickdeals.net/f/15749617-woods-6-outlet-wall-tap-adapter-3-25-free-store-pickup

I've used this. This is good price. It sticks to the outlet firmly. It has no USB-C/USB-A, but you don't need those. You can always buy those USB adaptars for < $10. Amazon sells these wall adpatars with USB-C/USB-A for $10 or so, but those are not worth the extra $7.

 

 

04/13/2022: Woot - skullcandy wireless earbuds for $14 (free shipping for Amazon Prime Members):

https://slickdeals.net/f/15720454-skullcandy-sesh-true-wireless-bluetooth-earbuds-13-99-free-shipping-for-prime-members-13-99?src=frontpage

Looks to have decent reviews, and best sound quality for under $20 earbuds.

 

 

04/09/2022: PC Connection - USB-C 64GB flash drives for $7:

https://slickdeals.net/f/15718033-kingston-usb-c-3-2-flash-datatraveler-drive-64gb-6-45-32gb-4-55-more-free-shipping?src=frontpage

It's hard to find USB-C drives for price of USB-A drives. It's a good price for 64GB ones. Kingston is a known brand.

 

 

04/09/2022: BestBuy - USB-C 90W wall charger with 8 feet cable for $25 (Now as of 04/11/2022, it's $11):

https://slickdeals.net/f/15717088-insignia-90w-usb-c-wall-charger-w-8-cable-in-store-pickup-24-99-at-bestbuy?src=frontpage

This is a great deal. You can charge or laptop/phone, etc very fast. It has 8 feet USB-C cable too, which by itself would cost about $10.

UPDATE: As of 04/11/2022, price has dropped to $11. There's a limit of 5 for online ordering. Get all of them, as it's crazy deal !!

https://slickdeals.net/f/15721309-insignia-90w-usb-c-fast-charging-wall-charger-8-cable-11-free-curbside-pickup?src=frontpage

 

 

04/09/2022: BestBuy - USB-C Portable Powerbank (~100Whr) for $40 :

https://slickdeals.net/f/15718651-insignia-26-800mah-usb-c-portable-charger-w-65w-power-delivery-39-99-free-shipping

This is a great deal. You can charge or laptop/phone, etc, and never have to worry about losing power. Best part is it's power capacity is just 100W-hr, so you can carry it on planes as carry on luggage. Airlines rules don't allow any battery over 100W-hr to be carried on flights (neither checkin nor carryon). Batteries are never allowed checkin luggage anymore, they always have to be in carryon luggage). "Open box- like new" are also avilable for $32.

UPDATE: As of 04/10/2022, the :open box like new" ones selling for $32 aren't available anymore for shipping. Orders getting cancelled.

 

03/31/2022: Microcenter (in store only) - MSI Katana laptop for $800:

https://slickdeals.net/f/15699310-new-customers-15-6-msi-katana-gf66-gaming-laptop-i7-11800h-rtx-3060-16gb-ram-1tb-ssd-144hz-ips-799-w-text-coupon-in-store-only-at-microcenter?src=frontpage

I usually don't go for laptops over $500, but with prices going up so high in 2021 for laptops, and dearth of laptops for < $500, this is a good deal as MSI makes good quality gaming laptops. You spend a bit more, but get lot more. 1 year std warranty + use your chase credit card to pay for it (that extends the warranty by an additional year). This is instore only deal, so you are out of luck if there's no microcenter store close by to you.

 

 

03/31/2022: Microcenter (in store only) - MSI Katana laptop for $800:

https://slickdeals.net/f/15699310-new-customers-15-6-msi-katana-gf66-gaming-laptop-i7-11800h-rtx-3060-16gb-ram-1tb-ssd-144hz-ips-799-w-text-coupon-in-store-only-at-microcenter?src=frontpage

I usually don't go for laptops over $500, but with prices going up so high in 2021 for laptops, and dearth of laptops for < $500, this is a good deal as MSI makes good quality gaming laptops. You spend a bit more, but get lot more. 1 year std warranty + use your chase credit card to pay for it (that extends the warranty by an additional year). This is instore only deal, so you are out of luck if there's no microcenter store close by to you.

 

 

03/29/2022: Target - 10 pack LED bulbs for $6 => expiry unknown

https://slickdeals.net/f/15694411-target-has-led-60w-10pk-light-bulbs-soft-white-up-up-free-store-pickup-or-free-shipping-for-red-card-holders-5-49

Not the cheapest, but at 50 cents per bulb, it's a good price. However, this is target brand, up&up, and based on reviews these may not last 5 years or more. They do have 1 yr warranty though. Better to wait for branded ones like GE, etc to go on clearance at Home Depot, Lowes, etc.

 

 

03/17/2022: BestBuy - Asus 17.3 inch chromebook laptop for $189:

https://slickdeals.net/f/15684649-asus-17-3-chromebook-intel-celeron-n4500-4gb-ram-32gb-emmc-189-or-less-w-sd-cashback-free-s-h

I'm not a fan of chromebook, and have always avoided buying them. However, this laptop just works great. It has 1080p screen, has usb-c charging (no separate power port,  but uses usb-c as power port), runs sleek even with multiple tabs open. The only downside is that permanent storage, (which is eMMC in this case, and NOT a hard drive) is small at 32GB. It can't be expanded as it's soldered. You can insert SD card upto 128GB (may be higher is also supported) and use that as extra hard drive storage. At $189 + 6% SD cashback, it's a very good value. Open box-Excellent is $10 less. You can always install linux and use it for your everyday task.

UPDATE 03/27/22: Now going for $149. A steal at this price, as it would cost more to make it for $149. Open box-Excellent is $10 less.

https://slickdeals.net/f/15693358-asus-17-3-chromebook-intel-celeron-n4500-4gb-ram-32gb-emmc-149-free-shipping?src=SiteSearch

 

 

2021:

 

 

12/01/2021: YMMV: Home Depot - AA/AAA batteries for 12 cents each:

 https://slickdeals.net/f/15469033-rayovac-60-pack-aa-or-aaa-batteries-7-49-home-depot-with-subscription-free-shipping?src=frontpage

This is YMMV, as not all HomeDepot stores have it.

 

 

11/26/2021: Newegg - 2 X 8gb DDR 4 memory sticks for $47

https://slickdeals.net/f/15407500-team-elite-16gb-2-x-8gb-260-pin-ddr4-3200-laptop-memory-cl-22-46-99-at-newegg-com?src=frontpage

This is not the lowest price for a 2X 8GB DDR4 memory, but decent enough if you need one.

 

 

11/14/2021: Walmart - 256 GB USB 3.0 flash drive for $20

https://slickdeals.net/f/15399019-sandisk-256gb-ultra-usb-3-0-flash-drive-19-28

This is the lowest price for a 256GB drive. It costs $0.08/GB. 1 TB of such drives will cost around $80 about on par with SSD drives. As I said, these are good to have as a backup to SSD. Buy at least 2 to get free shipping.

 

 

09/19/2021: OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries after rewards (expires 09/25/2021):

https://slickdeals.net/f/15289384-office-depot-officemax-100-back-in-rewards-duracell-coppertop-aa-aaa-16-pk-24-pk-batteries-limit-2-from-9-19-9-25?src=frontpage

This deal is going almost every week back to back.

Limit is 2. Better to buy 2 sets of 24 batteries (AA or AAA depending on need, you can mix and match). There's a coupon for 20% off to bring your total price for 48 batteries to $41. You will get around $41 in rewards. Each battery costs around 85 cents before rewards.

 

 

09/05/2021: OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries after rewards (expires 09/11/2021):

https://slickdeals.net/f/15263245-100-back-in-rewards-duracell-coppertop-aa-aaa-16-pk-24-pk-batteries-at-office-depot-from-9-5-21-to-9-11-21-11-59-pm-et

This deal is going almost every week back to back.

Limit is 2. Better to buy 2 sets of 24 batteries (AA or AAA depending on need, you can mix and match). There's a coupon "70407285" (for 20% off) to bring your total price for 48 batteries to $41. You will get around $41 in rewards. Each battery costs around 85 cents before rewards.

 

 

08/20/2021: Microcenter - Free 240 GB SSD drive, USB stick or MicroSD card (expiry unknown )

https://www.doctorofcredit.com/micro-center-sign-up-for-e-mail-newsletter-get-coupon-for-free-240gb-ssd-or-microsd-usb/

Insane deal for free !! It's at least $25 worth of stuff for free. Limit one per person. They are looking at your ID and stuff to enforce 1 per person rule. Microcenter stores are regional (not nationwide), so it's a deal only if you can drive to Microcenter.

 

 

08/15/2021: OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries + select school supplies after rewards (expires 08/28/2021):=> OK offer

https://slickdeals.net/f/15221659-office-depot-100-back-in-rewards-on-select-supplies-and-accessories-08-15-21-to-08-28-21-11-59-pm-et-limit-two-per-item-number

Limit is 2 per item. Lots od school supplies too. For batteries, limit is two in total - 2 sets of 18 batteries (AA or AAA depending on need, you can mix and match). There's 20% off coupon this time. Total price for 36 batteries would be $36. You will get around $36 in rewards. Each battery costs around $1 before rewards, which is pretty expensive. Other school supplies are free after rewards but it's hard to spend all that rewards without overpayning for a lot of junk over there. Wait for a better offer.

 

 

08/01/2021: OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries after rewards (expires 08/07/2021):=> OK offer

https://slickdeals.net/f/15196048-16-pk-duracell-coppertop-batteries-aa-aaa-100-back-in-rewards-19-40-more-free-store-pickup-office-depot-officemax

Limit is 2. Better to buy 2 sets of 24 batteries (AA or AAA depending on need, you can mix and match). There's no coupon this time. Total price for 48 batteries to $50. You will get around $50 in rewards. Each battery costs around $1 before rewards, which is the most expensive so far. Wait for a better offer.

 

 

07/18/2021: OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries after rewards (expires 07/24/2021):

https://slickdeals.net/f/15169375-again-at-office-depot-100-back-in-rewards-duracell-coppertop-aa-aaa-16-pk-24-pk-batteries-valid-in-store-online-from-7-18-21-to-7-24-21-11-59-pm-et-or-while-supplies-last

This deal is going almost every week back to back.

Limit is 2. Better to buy 2 sets of 24 batteries (AA or AAA depending on need, you can mix and match). There's a coupon "11589685" (for 20% off) to bring your total price for 48 batteries to $41. You will get around $41 in rewards. Each battery costs around 85 cents before rewards.

 

 

07/12/2021: OfficeDepot / OfficeMax - Free Non Rechargeable AA/AAA batteries after rewards (expires 07/17/2021):

https://slickdeals.net/f/15155977-12-count-duracell-optimum-batteries-aa-or-aaa-100-back-in-rewards-12-75-more-free-store-pickup?src=frontpage

Limit is 2. Better to buy 2 sets of 18 batteries (AA or AAA depending on need, you can mix and match). There's a coupon " 67901459 " (for 25% off) to bring your total price for 36 batteries to $33 You will get around $33 in rewards that you ahve to use in 90 days. Each battery costs around 90 cents before rewards.

 

 

07/01/2021: BestBuy - Non Rechargeable 36 pack AA/AAA batteries for $6 (expires 07/01/2021 => valid only for 1 day):

https://slickdeals.net/f/15135778-36-pack-insignia-alkaline-batteries-w-case-24-pack-aa-12-pack-aaa-5-95-free-store-pickup-at-best-buy?src=SiteSearch

24 AA + 12 AAA batteries. Not free, and costs about 18 cents per battery.

 

 

 

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Published: Monday, 12 July 2021 04:00
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Published: Friday, 02 July 2021 12:19
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DRAM Memory

When we talk about volatile memory, almost always we talk about DRAM (more specifically SDRAM). Wikipedia: https://en.wikipedia.org/wiki/Synchronous_dynamic_random-access_memory

Good article on basics of DRAM (taken from NXP): nxp_ddr_dram_basics

A DRAM memory module that you buy from market (long stick like with pins on one side) is a DIMM. It has multiple memory chips on it (usually 8 or 9). These are the actual memory chips that have the memory array in them. Each chip supplies 8 bits (or 16 bits in newer ones) of the DRAM bus. So, these 8 or 9 chips supply 64 or 72 bits (or 128 bits or more on newer ones) of the whole data bus.

Various gen of SDRAM:

1. SDR (or SDR SDRAM): This is the single data rate SDRAM. "SDRAM" term is also sometimes used for single data rate DRAM. However, SDRAM is usually meant for Synchronous DRAM. So, we should instead use "SDR SDRAM" for single data rate SDRAM. This was the 1st generation of DRAM which output data once every clock cycle (i.e data sent or received on only rising or falling edge). Clock speeds were from 66MHz to 133MHz. Supply Voltage was 3.3V.

2. DDR (or DDR SDRAM): This is the double data rate SDRAM. To double up the speed without increasing the clock speed, DDR SDRAM were introduced, which allowed data change to happen twice every clock cycle = once on rising edge and once on falling edge. This effectively doubled the bandwidth, as we would get the double the data rate even with the same clock speed.

JEDEC standard for naming memory chips:

So, specifying clock speed for memory chips wouldn't make sense, as that would imply that DDR memory have same speed as SDR memory (or they have the same bandwidth). So, JEDEC came up with a standard, which allowed effective speeds or bandwidth to be specified.

  • Speed convention: This specifies effective clock speed of memory module and has prefix as SDR/DDR followed by effective clock speed. It is of the form SDRxxxx or DDRxxxx where xxx refers to the effective clock speed of the memory stick. So, SDR mem with 200MHz was named SDR-200, while DDR mem with 200MHz was named DDR-400 (as 200MHz clk speed for DDR mem is effectively 400MHz clk speed as both rise/fall edges used). We also use nomenclature as DDR2-800 to further clarify that it's DDR2 memory.
  • Bandwidth convention: This specifies effective bandwidth (bytes/sec) of memory module and has PC as prefix followed by bandwidth in MB/sec. Memory chips were identified as PCxxxx where xxx refers to the effective bandwidth (in MB/Sec) of the memory stick. So, DDR2-800 memory stick which has 64 bit data interface is transferring 8bytes*800MHz = 6400MB/sec. So, it's named PC6400 or PC2-6400.

DDR Generations:

Various generation of DDR were introduced starting from year 2000. Below are the 5 gen of DDR memory as of 2020. None of the DDR mem are backwards compatible with SDR mem as the supply voltage was reduced from 3.3V which was the supply voltage of SDR mem. 

  • DDR1: Here, clock speeds were 133MHz to 200MHz. However, since data was rd/wrt twice every cycle, effective clock speed was 266MHz to 400MHz. Supply voltage was 2.5 V. For a 133MHZ SDR to be converted to DDR, clock rate of internal RAM operations wasn't changed. Instead, internally in SDRAM, 2 databits were pumped out on every +ve edge of clock cycle. This was done by allowing 2 parts of mem array to dump out the 2 bits in parallel. These were put in a 2 bit prefetch queue. Externally, the data bus grabbed bits from this prefetch queue 2 times every cycle, one on rising edge of clk, and other on falling edge of clk.
    • Typical DDR SDRAM clock rates are 133, 166 and 200 MHz (7.5, 6, and 5 ns/cycle), generally described as DDR-266, DDR-333 and DDR-400. Corresponding 184-pin DIMMs (having 64 bit or 8 byte data i/f) are known as PC-2100, PC-2700 and PC-3200. DDR-550 also available.
  • DDR2: DDR2 SDRAM is very similar to DDR1 SDRAM, but doubles the minimum read or write unit again, to four consecutive words. It does this by doubling the bus rate of the SDRAM without increasing the clock rate of internal RAM operations; instead, internal operations are performed in units four times as wide as SDRAM. The prefetch queue depth was doubled from 2 bits to 4 bits deep, so that internal memory can dump 4 bits of data every cycle (due to doubling of width of memory). So, from external memory i/f, 2 bits can be transferred with every cycle (one on rising edge and one on falling edge). Also, an extra bank address pin (BA2) was added to allow eight banks on large RAM chips. Supply voltage was 1.8 V. 
    • Typical DDR2 SDRAM clock rates are 200, 266, 333 or 400 MHz (periods of 5, 3.75, 3 and 2.5 ns), generally described as DDR2-400, DDR2-533, DDR2-667 and DDR2-800. Corresponding 240-pin DIMMs (still has 8 byte data i/f) are known as PC2-3200 through PC2-6400. DDR2-1066 and DDR2-1250 also available.
  • DDR3: DDR3 continues the trend, doubling the minimum read or write unit to eight consecutive words (prefetch queue depth of 8). This allows another doubling of bandwidth and external bus rate without having to change the clock rate of internal operations, just the width. Supply voltage was reduced to 1.5 V. DDR3 was mass adopted around 2008. DDR3 allowed max memory of 16GB per DIMM. DDR3 also has low voltage version called DDR3L which operates at 1.35V.
    • Typical DDR3 SDRAM clock rates are 400, 533, 666 or 800 MHz, generally described as DDR3-800, DDR3-1066, DDR3-1333 and DDR3-1600. Corresponding DIMMs (still has 8 byte data i/f) are known as PC3-6400 through PC3-12800. DDR3-2800 also available.
  • DDR4: DDR4 improves speeds further, but NOT by increasing the prefetch depth. Depth is still kept at 8, but banks are divided into more selectable bank groups where transfers to different bank groups may be done more rapidly. Internal banks are increased to 16 (4 bank select bits), with up to 8 ranks per DIMM. Supply voltage VDD/VDDQ was reduced to 1.2 V, with a 2.5 V auxiliary supply for wordline boost called VPP. DDR4 was introduced in 2014 and is still the most widely used memory as of 2022. DDR4 allowed max memory of 64GB per DIMM. DDR4 has NO low voltage version. DDR4 memory is supplied in 288-pin DIMMs, similar in size to 240-pin DDR3 DIMMs, by placing the pins more closely (0.85mm vs 1mm).
    • Typical DDR4 SDRAM clock rates are 800 to 1600 MHz, generally described as DDR4-1600 to DDR4-3200. DDR4-4800 also available.
  • DDR5: DDR5 is a major departure from previous gen mem, where it has active circuitry on the DIMM, which makes interface to the DIMM different from the interface to the RAM chips themselves. DDR5 DIMMs are supplied with management interface power at 3.3 V, and use on-board circuitry and associated passive components to convert to the lower voltage required by the memory chips. Final voltage regulation close to the point of use provides more stable power. Spec was released in 2020, and has yet to get mass adoption (a of 2022). Max DIMM capcity is 512GB.
    • Typical DDR5 SDRAM clock rates are 2400 MHz, generally described as DDR5-4800. It's quite a feat that we have clks running at 2.4GHz on PCB traces connecting 2 chips. Earlier, such Multi GHz clks could only run inside a chip generated locally from PLL.

 

Low Power DDR (LPDDR):

What we talked above was regular DDR mem used in laptops and desktops. LPDDR is a variant of DDR that consumes less power and is targeted for laptops, tablets and mobile phones. LPDDR technology standards are developed independently of DDR standards. LPDDR allows 16 and 32 bit data i/f in addition to 64 biit dat i/f that is std in regular DDR mem modules. Their mem capacity is smaller than their desktop cuounter parts as they are smaller in form factor.

  • LPDDR1: This is a slightly modified form of DDR1 to reduce power consumption. Power supply is reduced from 2.5V to 1.8V. LPDDR1 only had one voltage for all circuits (VDD) at 1.8 V. Additional savings come from temperature-compensated refresh (DRAM requires refresh less often at low temperatures), partial array self refresh, and a "deep power down" mode which sacrifices all memory contents. Additionally, chips are smaller, using less board space than their non-mobile equivalents.
  • LPDDR2: Similar to previous low power version, but more power efficient than DDR2. LPDDR2 created a separate voltage for the data bus (VDDQ), the command/address bus (VDDCA) and peripheral circuits (VDD2) at 1.2 V, keeping VDD (which powered the main memory array), now renamed to VDD1 at 1.8 V. We refer to operating voltage of LPDDR2 as 1.2V, even though the main interbal capcitive memory runs at 1.8V.
  • LPDDR3: LPDDR3 offers a higher data rate, greater bandwidth and power efficiency, and higher memory density. It went mainstream in 2013, running at 800 MHz DDR (1600 MT/s). At 64 bit data i/f, it implies 1600*8=12800MB/sec which is comparable to notebook memory from 2011. Samsung introduced the first 4Gbit 20nm DDR3 module capable of transmitting 2133MT/s. Supply voltages of LPDDR3 were same as those of LPDDR2.
  • LPDDR4: Doubling of i/f speed to 1600MHz (3200MT/s), and consuming 50% less energy. This was achieved partially by lowering VDDQ/VDD2 slightly to 1.1V, (from 1.2V)  removing VDDCA, but still keeping VDD1 at 1.8V. Hence we refer to operating voltage of LPDDR4 as 1.1V.
  • LPDDR5: Spec for LPDDR5 was published in 2019. It doubled the speed to 6400MT/s, and used differential clocking. It has bunch of power saving techniques. LPDDR5 created two possible values for VDD2, 0.9 V (low) or 1.05 V (high), depending on the frequency the memory is running, also allowing VDDQ to be between 0.3 V and 0.5 V. VDD1 was kept same as previous gens at 1.8V.

 

Graphics DDR (GDDR):

We talked about DDR mem above which are used mainly for cpu, but we also have DDR mem designed specifically for GPU, which require much higher bandwidth. These are called GDDR, and you see this mentioned on computers, which have a dicrete graphics card. Just like regular DDR gen, we have GDD1, GDDR2, etc. Transfer rate for GDR5 is about 100GB/sec.

 

DDR Memory interface and Commands:

The bus that connects the memory pins on microprocessor to the pins on the memory chip (DIMM on the motherboard) is known as the memory bus interface. There are bunch of cmds that are driven on these pins that dictate the operation.

There are 2 good articles on "Introduction to DRAM operation":

Intro to DRAM => https://www.allaboutcircuits.com/technical-articles/introduction-to-dram-dynamic-random-access-memory/

Basic operation => https://www.allaboutcircuits.com/technical-articles/executing-commands-memory-dram-commands/

Let's look at organization of DRAM memory chips and the DIMM:

DIMM: Contains multiple onboard DRAM chips. DIMM will have the memory size of DIMM as well as the organization detail as 2Rx8 etc.

  • DIMM module organization:
    • Rank: The rank of a DRAM module is the highest level of organization within a DIMM. A rank is a separately addressable set of DRAMs within a DIMM. In earlier chips, all DRAM chips on a DIMM would be addressed by a given addr. This was because each DRAM chips provided some bits of the final data bus that was output from the DIMM. In case of DIMM with 64 bit data bus o/p, 8 DRAM chips each 8 bit wide would provide 64 bits. So, Rank of chip was 1. However, later with memory capacity increasing and more and more DRAM chips on a single DIMM, we could separate out the DRAM chips into groups, where each group behaved like a single DIMM. One group has no relation to other group. So, ranks can be considered to be like different DIMM, except that they are physically on a single board.
  • DRAM chip organization:
    • Bank: Bank is the next level of organization below a rank. Bank is organization of memory arrays within a DRAM chip. So, while Rank refers to organization at DIMM level, banks refers to organization at DRAM chip level. Each bank operates independently of the others. This means that reading, writing, and precharging can all be done on one bank without impacting the other. Each bank may have multiple memory arrays, where each array is a set of rows and columns of memory. Each memory array outputs 1 bit, so the size of the output width of a bank indicates the number of arrays it has. Therefore in a x4 DRAM chip, the internal banks would each have four memory arrays. Only 1 bank is accessed at a time in each dram chip, so banks can be thought of as ranks within a DRAM chip.
      • NOTE: Multiple Banks may also be combined to form a Bank Group.
    • Rows/Columns: Banks are further divided into rows and columns, which are grouped into memory arrays. Each memory array outputs 1 bit as explained above.

 

DRAM Chip Interface:

Though pins for DRAM chips vary a little from gen to gen and among different vendors, there are few pins that are fundamental to operation of DRAM. Most of these pins are provided as differential signal (i.e complimentary signals in pair) as that provides btter noise immunity. Major pins of DRAM are:

  • Clock: This is the main clock provided as i/p to the DRAM chip.
    • CMD/ADDR CLK CK (Differential clock signal, i/p): This is pair of clock signals sent to the DRAM chip that is used to sample all the i/p signals for control and Addr (NOT to latch data signals) as shown below. This is differential (i.e +ve and -ve clk) so that it has better noise immunity. Historically clk has always been provided as differential pair, as clk needs to be very clean and free of glitches, else wrong values may get captured. Cmd/Addr are sampled on both edges of clk, so this is ddr clk. Cmd/Addr signals are lower speed, so this clk is usually slower than dataclk discussed later.
    • Clock Enable CKE => Some early generation of chips had a separate clock en pin, which would enable clk when when this pin was high. CKE was pulled low for auto/self refresh cmd as those cmds didn't need a clk.
    • WRT DATA CLK WCK (Differential clock signal, i/p): This is pair of clock signals sent to the DRAM chip for Write data capture and Read data output. CMD/ADDR clk is a separate clk (discussed above) that can't be used as wrt data clk, as wrt data clk is 2X-4X faster to support higher freq writes. This clk is also used for outputting read data and read strobe signal from the DRAM chip back to SOC. Wrt data is centered b/w the rise and fall edge of wrt clk.
  • Control/Addr: These are control signals that determine the action to take.
    • Chip Select CS# (active low i/p) => This activates the selected DRAM chip when low. All other DRAM chips with CS# high are not activated. At the DIMM level, there is a bus of CS#[x:0] coming in, which goes thru a decoder, and that decides which DRAM chip to select. This is sampled on rising edge of Cmd/Addr clk.
    • Cmd/Addr CA[x:0] (i/p bus) => This is a bus that serves dual purpose. It has cmd phase and Addr phase. Various cmds such as read, write, precharge, etc are sent on cmd bus, followed by the Addr to which this cmd applies to. This is the most common approach on latest gen of DDR, though earlier chips had many more pins to achieve the same purpose. Some of these are listed below:
      • Bank Addr BA[x:0] => Since we may have multiple banks, there is a separate bank addr too on some of the chips. Bank Addr bus may be considered part of the same Addr bus, as it's functionally just one big set of addr.
      • Row/Col addr strobe RAS#/CAS# (active low i/p)=> For Addr, we didn't separate out row/col addr. Both of them are embedded into the Addr bus. Row and col addr are provided in 2 separate cycles. The cmd protocol itself may define which is col addr and which is row addr. In many chips, we have dedicated pins called RAS# (Row addr strobe) and CAS# (column addr strobe) which indicate when row addr is going on the Addr bus and when col addr is flowing on Addr bus. Both RAS# and CAS# are active low.
      • Write Enable WE# (active low i/p) => We need a separate line for saying whether it's read or wrt. When low, it indicates a Rd cmd, while high indicates a wrt cmd. RAS, CAS and WE together define a cmd. Now these are all embedded within CA[x:0] bus.
  • Data: This refers to Data signals to Rd or Write. There's also a strobe signal that goes with this data bus, that serves as the clk for the data signals
    • Data DQ[x:0] (bidirectional bus) => This is Data bus that carries the data to be written to memory (in case of write cmd) or data read from memory (in case of read cmd). Optional ECC (Error correcting Code) bits are also provided on few of these lines to help with Error correction. This bus is bidirectional.
    • Data Strobe DQS[x:0] (bidirectional bus) => This is the strobe signal for Data bus. Since clk is already provided to the DRAM chip as i/p to latch all incoming signals, the same clk may be used as the clk for latching the rd/wrt data. The problem is that clk may be shifted and not perfectly aligned. So, a separate strobe for rd/wrt is needed. Write data and strobe are both driven by same clk on SOC (system on chip) chip, but are aligned with help of a DLL (Delay lock loop). This data strobe is used to latch wrt data on the DRAM chip. However, if we have separate clk lines for wrt (Wrt Data Clk), then we don't need strobe for write, in which case, this strobe signal is only used for Rd. For read, we do the same thing as wrt. Rd data and strobe are both driven by same clk (wrt clk) on DRAM chip, but are aligned with help of a DLL (Delay lock loop). This data strobe is used to latch rd data on the SOC chip. For this reason, DQS is bidirectional. DQS is edge aligned with read data, but centered in wrt data.
    • Data Mask DM[x:0] => These are data mask bits that can be used to mask data bytes that we don't want to write to DRAM chip. Since DM bits are similar to Wrt Data bits, they are also latched using Data strobe. Mask bits are usually on per byte basis. These Mask bits may also have other function, when wrt is not taking place.
  • Power: This refers to power supply and gnd signals.
    • VDDQ/VSSQ => These are the power supply for o/p ports of the DRAM chip. i/p ports will also need this power supply for the level shifter before the signal gets into the internal power domain. DRAM IO power follows the level of VDDQ input.
    • VDD/VSS => These are to power everything else except the IO ports. All internal circuitry, peripheral logic, DRAM memory, etc is running of this supply. These were subdivided into 2 parts after few gen to save power:
      • VDD1 => This is the main power that powers the capacitive memory array. The voltage here is usually the highest. Most critical voltage as memory array rd/wrt speed dependent on this voltage.
      • VDD2 => This is the peripheral power which powers all logic which are not on IO and not in capacitive memory array. This is kept lower than VDD1 to save on power. It can be lowered even further depending on Freq requirement of the DRAM.
    • VREF => This is a reference voltage provided as input.

 

DRAM Basic cmds:

Though there are many cmds in the latest gen of DRAM chips, these are few basic cmds that are needed for all DRAM chips. In chips, which have separate cmd pins, combo of CAS, RAS, We and CKE determine what cmd is going to be executed. In newer gen chips, this cmd is embedded within the cmd bus, as there are no separate cmd pins. Below are the 5 basic cmds for any rd or wrt to take place. We start with Activate phase, followed by precharge, then a rd/wrt takes place. Auto Refresh happens in parallel every so often to preserve DRAM values.

  • Activate (row access): Activate is essentially the row access command. Meaning, it opens up a row and moves the charge from the capacitors into the sense amplifiers. Accessing a row is always done before a column in DRAM. This command is paired with inputs to a bank address register (that selects the current bank) and a row address register (that selects the desired row). One important note on the activate command is that whichever row is currently open remains open until a precharge command is issued (more on precharge later). To use this command most DRAMs require CS and RAS to be pulled low, while CAS and WE are pulled high.
  • Precharge (row precharge): Precharge deactivates the row currently open in a bank. When issued a precharge command, the DRAM is told to restore the values read from the row of capacitors. This is done by the sense amplifiers and when completed prepares the bank for another row access. Precharge is performed by pulling CS, RAS, and WE low and leaving CAS high.
  • Read (col access): The read command can also be thought of as a column read command. When combined with a proper bank address and column address, the data recently moved into the sense amplifiers from an activate command (row access) is now pushed onto the data bus. DRAMs often include a “Read and Auto-Precharge” command that performs the column read and then closes/precharges the row. This way, a separate precharge command need not be issued. If the same row, but a different column, needed to be accessed then a precharge would not be issued at all and the row would be left open. To use the read command CS and CAS are pulled low, while RAS and WE are pulled high. 
  • Write (col access): A write command is virtually the same as a read, except for the direction of the data. During a write command, data is pulled off of the data bus and put into the selected bank, row, and column. Auto-precharging can be performed much like a read and closes the currently activated row when the write is done. To perform a write, CS, CAS, and WE are pulled low, while RAS is held high.
  • Auto Refresh: In DRAM, the refresh command is issued every so often. It's needed since DRAM bits loses charge over time (irrespective of whether it's accessed or not). All bits will need to be refreshed every so often. One important aspect of refreshing is that any active banks should be precharged before the command is issued. To perform a refresh CS, RAS, and CAS are pulled low with WE high. After refreshing, the DRAM keeps track of the last refreshed row and increments a refresh counter so that the next refresh command will operate on the next row. When a refresh command is issued, the current row in every bank is refreshed. Most DRAMs will perform 8192 refresh cycles every 64 ms. That's every 7.813 μs. This has remained constant despite growing device densities. 
  • Other Cmds: Other common DRAM commands include NOP (No Operation), Burst Terminate, and Load Mode Register. NOP is used to force the DRAM to do nothing. This is useful when the DRAM needs to wait, for instance if it is currently being refreshed. In reality, read and writes to DRAM are done in short bursts. Burst terminate will truncate the read or write command, i.e., stop it prior to finishing. DRAM can be placed into different modes. These modes are changed via the Load Mode Register command.

 

LPDDR5:

 We'll look at LPDDR5 Memory i/f from JEDEC spec: (JEDEC spec is only available to members, but I'll list imp stuff below):

 

 

 

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Published: Friday, 25 June 2021 18:55
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Selected websites for practice:

A lot of websites advertise "free sample papers" for practicing, but soon you realize that these are for profit websites, and want your money. You should not have to pay for any educational resource in today's internet era. So, I've compiled a list below of free practice papers. I've listed papers starting from Elementary School to High School. Advanced Maths papers beyond High School will be in their respective sections.

1. STAAR tests: In Texas, students have to pass STAAR test in order to move to next grade. These question papers are available for free here, so that you can see the complexity of questions expected. Look for Maths papers from Grade 3 to High School:

https://tea.texas.gov/student-assessment/testing/staar/staar-released-test-questions

2. math-only-math website: This website is mentioned under maths section: https://www.math-only-math.com/. This has lots of sample questions for each grade and for each topic. I don't think you can find more comprehensive material than this for practicing.

3. Math10 website: Math10 has questions for each grade and each topic, separated out under easy, medium and hard. Link => https://www.math10.com/problems/

4. mathoplis website: This website is mentioned under maths section: https://www.mathopolis.com/questions/skills.php and https://www.mathopolis.com/questions/quizzes.php

5. Khan Academy: Last, but the best. It not only has teaching videos, but tons of practise material for all grades. There is course challenge for each subject in each grade, that you find once you go that grade and that subject. One such example for 8th grade maths is here:

https://www.khanacademy.org/math/8th-grade-illustrative-math#8th-grade-illustrative-math-subject-challenge

On each topic of each subject, there is a separate quiz, and mastery questions, which are very helpful. Each lesson is accompanied by "practice questions" and a "quiz". This helps you as you watch videos and solve these questions.

6. byjus website: CBSE (India) sample papers for 8th grade: The questions are harder compared to 8th grade in USA. Link => https://byjus.com/cbse-sample-papers-for-class-8-maths/

 

Sample papers for practice:

Few other sample maths papers picked from internet. I've provided a link, as well as downloaded the document to my server, and provided a link. That way, if the online document disappears (as it happens quite frequently)

A. Baschools:

8th grade: Downloaded from here: https://www.baschools.org/pages/uploaded_files/Pre-Algebra%20Practice%20Test.pdf  => Local copy => Maths-8th-grade-Pre-Algebra-Practice-Test.pdf

B. ne.gov: (nebraska state)

8th grade: Download from here: https://www.education.ne.gov/wp-content/uploads/2017/07/NEG8MathPTPaper.12.06.10.pdf => Local copy => NEG8MathPTPaper120610.pdf

C.Louisiana believes: This is one of the highest quality maths papers that you can find anywhere. If the kid can solve almost all questions here, he's good for that grade:

All Sample papers from 3rd grade to 8th grade are provided here: https://louisianabelieves.com/resources/library/practice-tests

The link above does have sample papers, but hard to navigate. So, I provided pdf links separately for some of the maths ones.

5th grade: Download from here: http://www.stjames.k12.la.us/common/pages/displayfile.aspx?itemid=12921575

6th grade: Download from here: https://louisianabelieves.com/docs/default-source/assessment/leap-connect-grade-6-math-practice-test-reference-materials.pdf?sfvrsn=fc32991f_2

7th grade: Download from here: http://www.stjames.k12.la.us/common/pages/displayfile.aspx?itemid=12921698

 8th grade: Download from here: https://www.louisianabelieves.com/docs/assessment/practice-test-math-grade-8.pdf => Local copy => practice-test-math-grade-8.pdf

D. everestva: Lots of sample papers here (both US as well as papers from India too)

https://everestva.com/search/grade-8-maths-exam-papers-and-answers-pdf

Some sample papers from above website:

1. Nebraska state, USA: Need one paper: FIXME ..

2.Australia, Kinross college: Download from here: https://kinrosscollege.wa.edu.au/wp-content/uploads/2017/11/Year-8-Maths-Exam-Sem-2-2016.pdf

=> Local copy => Year-8-Maths-Exam-Sem-2-2016.pdf

3. south africa (zambia): Download from here: https://www.education.gov.za/Portals/0/CD/Curriculum%20doc%20question%20Papers2007/2015%20ANA%20Gr%208%20Mathematics%20Test%20-%202015.pdf?ver=2015-08-05-213322-000

=> Local copy => 2015_ANA_Gr_8_Mathematics_Test_-_2015.pdf

4. namibia (grade 8 + grade 9): Download from here: http://www.nied.edu.na/assets/documents/02Syllabuses/04JuniorSecondary/Mathematics/JS_Math_Specimen_Papers1_and_2_March_2018.pdf

=> Local copy => JS_Math_Specimen_Papers1_and_2_March_2018.pdf

5. zambia:  Download from here:   https://www.mathsatsharp.co.za/wp-content/uploads/2015/10/November_Exam_2015_Grade_8.pdf

=> Local copy => November_Exam_2015_Grade_8.pdf

6. Australia (Acara): Bunch of papers from past couple years. Choose "numeracy" for maths papers. Year 9 might be for 8th grade students, though questions look simple. Link to download all the papers: https://www.acara.edu.au/assessment/naplan/naplan-2012-2016-test-papers

E. UK School papers: Few sample papers which look to be at Middle school level:

https://examberrypapers.co.uk/resources/free-11-plus-practice-papers/maths/

 

 

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