Modern Operating Systems by Herbert Bos ...
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 46
SEC. 1.2
1.2.4 The Fourth Generation (1980–Present): Personal Computers
With the development of
Large Scale Integration
) circuits—chips con-
taining thousands of transistors on a square centimeter of silicon—the age of the
personal computer dawned. In terms of architecture, personal computers (initially
) were not all 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 possible for a single individual
to have his or her own personal computer.
In 1974, when Intel came out with the 8080, the first general-purpose 8-bit
CPU, it wanted an operating system for the 8080, in part to be able to test it. Intel
asked one of its consultants, Gary Kildall, to write one.
Kildall and a friend first
built a controller for the newly released Shugart Associates 8-inch floppy disk and
hooked the floppy disk up to the 8080, thus producing the first microcomputer with
a disk. Kildall then wrote a disk-based operating system called
Program for Microcomputers
) for it. Since Intel did not think that disk-based
microcomputers had much of a future, when Kildall asked for the rights to CP/M,
Intel granted his request. Kildall then formed a company, Digital Research, to fur-
ther develop and sell CP/M.
In 1977, Digital Research rewrote CP/M to make it suitable for running on the
many microcomputers using the 8080, Zilog Z80, and other CPU chips. Many ap-
plication programs were written to run on CP/M, allowing it to completely domi-
nate the world of microcomputing for about 5 years.
In the early 1980s, IBM designed the IBM PC and looked around for software
to run on it. People from IBM contacted Bill Gates to license his BASIC inter-
They also asked him if he knew of an operating system to run on the PC.
Gates suggested that IBM contact Digital Research, then the world’s dominant op-
erating systems company. Making what was surely the worst business decision in
recorded history, Kildall refused to meet with IBM, sending a subordinate instead.
To make matters even worse, his lawyer even refused to sign IBM’s nondisclosure
agreement covering the not-yet-announced PC.
Consequently, IBM went back to
Gates asking if he could provide them with an operating system.
When IBM came back, Gates realized that a local computer manufacturer,
Seattle Computer Products, had a suitable operating system,
Disk Operat-
ing System
). He approached them and asked to buy it (allegedly for $75,000),
which they readily accepted. Gates then offered IBM a DOS/BASIC package,
which IBM accepted.
IBM wanted certain modifications, so Gates hired the per-
son who wrote DOS, Tim Paterson, as an employee of Gates’ fledgling company,
Microsoft, to make them. The revised system was renamed
Disk Operating System
) and quickly came to dominate the IBM PC market. A
key factor here was Gates’ (in retrospect, extremely wise) decision to sell MS-DOS
to computer companies for bundling with their hardware, compared to Kildall’s

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