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Modern Operating Systems by Herbert Bos and Andrew...
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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 748
SEC. 10.1
located on the fifth floor at Bell Labs. The Interdata was on the first floor.
ating a new version meant compiling it on the fifth floor and then physically carry-
ing a magnetic tape down to the first floor to see if it worked. After several months
of tape carrying, an unknown person said: ‘‘You know, we’re the phone company.
Can’t we run a wire between these two machines?’’ Thus, was UNIX networking
born. After the Interdata port, UNIX was ported to the VAX and later to other com-
After AT&T was broken up in 1984 by the U.S. government, the company was
legally free to set up a computer subsidiary, and did so. Shortly thereafter, AT&T
released its first commercial UNIX product, System III.
It was not well received,
so it was replaced by an improved version, System V, a year later. Whatever hap-
pened to System IV is one of the great unsolved mysteries of computer science.
The original System V has since been replaced by System V, releases 2, 3, and 4,
each one bigger and more complicated than its predecessor.
In the process, the
original idea behind UNIX, of having a simple, elegant system, has gradually
diminished. Although Ritchie and Thompson’s group later produced an 8th, 9th,
and 10th edition of UNIX, these were never widely circulated, as AT&T put all its
marketing muscle behind System V.
However, some of the ideas from the 8th, 9th,
and 10th editions were eventually incorporated into System V.
AT&T eventually
decided that it wanted to be a telephone company after all, not a computer com-
pany, and sold its UNIX business to Novell in 1993.
Novell subsequently sold it to
the Santa Cruz Operation in 1995.
By then it was almost irrelevant who owned it,
since all the major computer companies already had licenses.
10.1.4 Berkeley UNIX
One of the many universities that acquired UNIX Version 6 early on was the
University of California at Berkeley. Because the full source code was available,
Berkeley was able to modify the system substantially. Aided by grants from ARPA,
the U.S. Dept. of Defense’s Advanced Research Projects Agency, Berkeley pro-
duced and released an improved version for the PDP-11 called
Berkeley Software Distribution
). This tape was followed quickly by another, cal-
, also for the PDP-11.
More important were
and especially its successor,
for the VAX.
Although AT&T had a VAX version of UNIX, called
, it was essentially Ver-
sion 7.
In contrast, 4BSD contained a large number of improvements. Foremost
among these was the use of virtual memory and paging, allowing programs to be
larger than physical memory by paging parts of them in and out as needed. Anoth-
er change allowed file names to be longer than 14 characters.
The implementation
of the file system was also changed, making it considerably faster. Signal handling
was made more reliable.
Networking was introduced, causing the network proto-
col that was used,
, to become a de facto standard in the UNIX world, and
later in the Internet, which is dominated by UNIX-based servers.

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