History Of Operating System : The Fourth Generation

The Fourth Generation (1980-Present) : Personal Computers.

With the development of LSI (Large Scale Integration) circiuts, chpis containing thousands of transistors on a square centimeter of silicon, the age of the personal computer dawned. In terms of architecture, personal computers were not that different from minicomputers of the PDP-11 class, but in terms of price they certainly were different. Where the minicomputer made it possible for a department in a company or university to have its own computer, the microprocessor chip made it posibble for a single individual to have his or her own personal computer. The most powerful computers used by businesses, universities, and goverment installations are usually called workstations, but they are really just large personal computers. Usually, they are connected together by a network.

The widespread availability of computing power, especially highly interactive computing power usually with excellent graphics, led to the growth of a major industry producing software for personal computer. Much of this software was userfriendly meaning that it was intended for users who not only knew nothing about computers but furthermore had absolutely no intention whatsoever of learning. This was certainly a major change from OS/360, whose job control language, JCL, was so arcane that entire books were written about it (e.g., Cadow, 1970).

Two operating systems initially dominated the personal computer and workstation scene : Microsoft's MS-DOS and UNIX. MS-DOS and UNIX. MS-DOS was widely used on the IBM PC and other machines using the Intel 8088 CPU and its successors, the 80286, 80386, and 80486 (which we will refer to henceforth as the 286, 386, and 486, respectively), and later the Pentium and Pentium Pro. Althoughthe initial version of MS-DOS was relatively primitive, subsequent versions have included more advanced features, including many taken from UNIX. Microsoft's successor to thana true operating system is WINDOWS NT, which is compatible with WINDOWS 95 at a certain level, but a complete rewrite from scratch internally.

The other major contender is UNIX, which is dominant on workstations and machines powered by high-performance RISC chips. These machines usually have the computing power of a minicomputer RISC chips. These machines usually have the computing power of minicomputer, even though they are dedicated to a single user, so it is logical that they are equippped with an operating system originally designed for minicomputers, namely UNIX.

An interesting development that began taking place during the mid-1980s is the growthof networks of personal computer running network operating systems and distributed operating systems (Tanenbaum, 1995). In a network operating system, the users are aware of the existance of multiple computers and can log on to remote machines and copy files from one machine to another. Each machines runs its own local operating system and has its own local user (or users).

Source : Book - "Operating Systems : Design and Implemetation"
By Andrew S. TanenBaum and Albert S.Woodhull