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Unix: Introduction
• Unix first developed in 1969 at Bell Labs (Thompson & Ritchie).
• Originally written in PDP-7 asm, but then (1973) rewritten in the ‘new’ high-level language C.
⇒ easy to port, alter, read, etc.
•6th edition (“V6”) was widely available (1976).
– source avail
⇒ people could write new tools.
– nice features of other OSes rolled in promptly.
• By 1978, V7 available (for both the 16-bit PDP-11 and the new 32-bit VAX-11).
• Since then, two main families:
– AT&T: “System V”, currently SVR4.
– Berkeley: “BSD”, currently 4.3BSD/4.4BSD.
• Standardisation efforts (e.g. POSIX, X/OPEN) to homogenise.
• Best known “UNIX” today is probably linux, but also get FreeBSD, NetBSD, and
(commercially) Solaris, OSF/1, IRIX, and Tru64.

Design Features

Ritchie and Thompson writing in CACM, July 74, identified the following (new)

features of UNIX:

1. A hierarchical file system incorporating demountable volumes.

2. Compatible file, device and inter-process I/O.

3. The ability to initiate asynchronous processes.

4. System command language selectable on a per-user basis.

5. Over 100 subsystems including a dozen languages.

6. A high degree of portability.

Features which were not included:

• real time

• multiprocessor support

Fixing the above is pretty hard.

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