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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 746
SEC. 10.1
discarded PDP-7 minicomputer. Despite the tiny size of the PDP-7, Thompson’s
system actually worked and could support Thompson’s development effort. Conse-
quently, one of the other researchers at Bell Labs, Brian Kernighan, somewhat jok-
ingly called it
UNiplexed Information and Computing Service
Despite puns about ‘‘EUNUCHS’’being a castrated MULTICS, the name stuck, al-
though the spelling was later changed to
10.1.2 PDP-11 UNIX
Thompson’s work so impressed his colleagues at Bell Labs that he was soon
joined by Dennis Ritchie, and later by his entire department. Two major develop-
ments occurred around this time.
First, UNIX was moved from the obsolete PDP-7
to the much more modern PDP-11/20 and then later to the PDP-11/45 and
PDP-11/70. The latter two machines dominated the minicomputer world for much
of the 1970s.
The PDP-11/45 and PDP-11/70 were powerful machines with large
physical memories for their era (256 KB and 2 MB, respectively). Also, they had
memory-protection hardware, making it possible to support multiple users at the
same time. However, they were both 16-bit machines that limited individual proc-
esses to 64 KB of instruction space and 64 KB of data space, even though the ma-
chine may have had far more physical memory.
The second development concerned the language in which UNIX was written.
By now it was becoming painfully obvious that having to rewrite the entire system
for each new machine was no fun at all, so Thompson decided to rewrite UNIX in
a high-level language of his own design, called
B was a simplified form of
BCPL (which itself was a simplified form of CPL, which, like PL/I, never worked).
Due to weaknesses in B, primarily lack of structures, this attempt was not suc-
cessful. Ritchie then designed a successor to B, (naturally) called
, and wrote an
excellent compiler for it. Working together, Thompson and Ritchie rewrote UNIX
in C.
C was the right language at the right time and has dominated system pro-
gramming ever since.
In 1974, Ritchie and Thompson published a landmark paper about UNIX
(Ritchie and Thompson, 1974).
For the work described in this paper they were la-
ter given the prestigious ACM Turing Award (Ritchie, 1984; Thompson, 1984).
The publication of this paper stimulated many universities to ask Bell Labs for a
copy of UNIX. Since Bell Labs’ parent company, AT&T, was a regulated
monopoly at the time and was not permitted to be in the computer business, it had
no objection to licensing UNIX to universities for a modest fee.
In one of those coincidences that often shape history, the PDP-11 was the com-
puter of choice at nearly all university computer science departments, and the oper-
ating systems that came with the PDP-11 were widely regarded as dreadful by pro-
fessors and students alike. UNIX quickly filled the void, not least because it was
supplied with the complete source code, so that people could, and did, tinker with
it endlessly. Scientific meetings were organized around UNIX, with distinguished

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