History of UNIX
a short version
CSCI 333
August 31, 2011
Before UNIX
 In the 40’s and 50’s, all
computers were “personal
computers”
 That is, one person signed
up for an hour of
computing time
 In the 60’s, batch systems
with punched cards were
the way of life
Multics
 In 1965, a collaborative project by
GE, MIT and AT&T
 Goal: Create an operating system to
“show that general-purpose, multiuser, timesharing systems were
viable.”
 Name: Multics (Multiplexed
Information and Computing Services)
Multics
 In 1969, frustrated by slow progress,
AT&T pulled out of the project
 Ken Thompson, of AT&T, needed
something interesting to do
 He took over an unused DEC PDP-7
(minicomputer) and pursued some of
the Multics ideas on his own (most of
which were shot down by AT&T)
Ken Thompson
 The code was written using assembly
language
 It was much simpler than Multics
 It was good at running programs
 Another researcher at Bell Labs
jokingly referred to it as UNICS
(Uniplexed Information and
Computing Services)
Dennis Ritchie
 In 1970, Thompson along with Dennis
Ritchie and others, rewrote UNIX for
a new PDP-11 (this was the dominant
minicomputer in the 70’s...it had 24K
RAM, 12K of which for UNIX…it only
cost a mere $65,000)
 More tools were added, such as a
shell, editor, assembler, utilities like
rm, cat, and cp
B
 In 1972, Thompson wrote B, a very
simple programming language
 He got it going on the PDP-7 because
Fortran wouldn’t work for him
 He wanted to re-write UNIX in a highlevel language
C
 In 1972, Ritchie used the PDP-11 to
add types to B
 Initially, it was called NB, “New B”
 Then, he wrote the compiler
 The C programming language was
born
 C was designed to be simple and
portable
Re-writing UNIX
 In 1973, Thompson re-wrote UNIX using C
 Operating systems written in assembly
language consisted of hardware-dependent
code
 An operating system written in a high-level
language, such as C, allowed it to be
portable
 The kernel consisted of 10,000 lines of code
 Many features of other O.S. kernels were
left out of the UNIX kernel (e.g., the
command language ran as a user process)
The spread of UNIX
 In 1974, Ritchie and Thompson
published a paper about UNIX
 Many universities were interested
 AT&T licensed UNIX for a modest fee
 Releases were distributed as C source
code
 By 1977, more than 500 sites (125
universities) were running UNIX
BSD
 Graduate students at the University of
California Berkeley began making
significant enhancements to the source
code
 In 1978, they released 30 copies of their
Berkeley Software Distribution (BSD):
 Easy to switch between programs
 Longer filenames (255 vs. 14)
 Easy to connect UNIX machines to LANs
Versions / Flavors of UNIX
 Under agreement with AT&T, organizations
could release minor updates without
renegotiating contract
 DEC and Sun adopted the Berkeley UNIX
 Data General, IBM, HP, and Silicon
Graphics were among those that adopted
the AT&T (“standard”) System V
 In 1980, Microsoft developed XENIX
 In the early 90s, Linux and Solaris were
created
Different versions of UNIX
 To find out what you are responsible
for knowing about UNIX versions on
Exam #1, click on the link below:
 Exam #1 Outline
 IEEE Portable Operating System
Interface (POSIX) is an attempt to
standardize UNIX (among other
things)
Pioneers of computing…today