Details

Published: Wednesday, 28 November 2018 17:48

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History:

First generation (1945-55): These computers were made of vacuum tubes and had plugboards. Machine language was directly wired using plugboards.

Second generation (1955-65): These computers were made of transistors. Program could be written on paper (in fortran or assembler), and jobs were submitted in batch. There were compiler and rudimentary Operating system (OS). OS is layer of Software (SW) whose job is to manage all the devices in a computer system (processor, memory, disk, keyboard, I/O devices, etc) and provide user programs with a simpler interface to hardware.

Third generation (1965-80): These computers were made of ICs. IBM developed the 360 series which used common OS/360 SW. These computers introduced Multiprogramming where multiple jobs could run at the same time. Timesharing was also introduced where multiple users could login. MULTICS system was developed at Bell Labs whose SW was written in PL/I. It wasn't a success as the compiler for PL/I was buggy.

One of the scientists at Bell Labs, Ken thompson, found a small PDP-7 computer and sat down to write stripped down, one user version of MULTICS, which subsequently developed into UNIX OS. 2 major versions of unix developed: System V from AT&T and BSD from UCAL, Berkeley. However, these were not free. S. Tanenbaum wrote a clone of unix, called minix, which was free, but was just for educational purposes. Desire for free production version of minix led a finnish student, Linus Tarvolds, to write Linux.

Fourth generation (1980-present): Personal computers came into existence. In 1974, Intel came out with 8080, the first general purpose 8 bit CPU. Gary Kildall from Intel, wrote a disk based OS called CP/M and formed a company Digital Research to further develop CP/M. It dominated the world of microcomputing for next 5 yrs.

In early 1980, IBM designed IBM PC and looked around for software to run on it. Kildall refused to provide his OS. Bill Gates bought DOS (disk OS) from a seattle company and sold IBM a DOS/BASIC package, since he was already licensing his Basic interpreter to IBM. IBM wanted some modifications, so Gates hired Tim Paterson, who wrote DOS, to do it. Revised system was named MS-DOS and came to dominate the IBM-PC market as Gates started selling MS-DOS to computer companies for bundling with their hardware.

MS-DOS was widely used on 80286, 80386 and 80486. However, all these early OS were based on users typing in commands from keyboard. However, all this changed Englebart invented GUI which was adopted by XEROX. One day, Steve Jobs of Apple computer visited PARC and saw this. He saw it's potential value and built Apple Macintosh based on GUI, which was a huge success.

When Microsoft decided to build a successor to MS-DOS, it also built a GUI based system called Windows, which originally ran on top of MS-DOS (it was more like a shell than a true OS). For about 10 yrs from 1985-1995, Windows was just a graphical environment on top of MS-DOS. For about 10 yrs from 1985-1995, Windows was just a graphical environment on top of MS-DOS. However, starting in 1995, a free standing version of Windows, Windows 95, was released that incorporated many new OS features, using underlying MS-DOS system only for booting and running old MS-DOS programs. In 1998, a slightly modified version called Windows 98 was released. However, both of these contained a large amount of 16 bit Intel Assembly language. So, a full 32 bit OS was written from scratch and was called Windows NT (New Technology), designed by David Cutler. Version 4 of Windows NT called Windows NT 4.0 became poular. Version 5 of Windows NT was renamed Windows 2000 in early 1999.

Powering up of PC:

When the system is first powered up, Reset signal is asserted until the power supply output voltages have stabilized. The values of various registers are forced on reset. Since CR0 contains 0x00000010h, processor starts in Real Mode, is not aware of FPU and paging is disabled. DS, ES, FS, GS, SS, ESP, IDTR, CR2 and CR3 contain 0. CS contains F000h and EIP contains 0000FFF0h.

Booting process: Good link is here .