UNIX Second Edition

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Unix V2
Type: Multi-tasking, multi-user
Creator: AT&T/Western Electric
Architecture: PDP-11
Previous Version: V1
This Version: V2
Next Version: V3
Date Released: June, 1972

UNIX Second Edition (often referred to as UNIX V2 or V2 UNIX - 'Unix' was still normally given in all capital letters at this point in time) was an early version of UNIX. There were 10 instances of UNIX running inside Bell at this point.

It still ran on the PDP-11/20 model of the PDP-11; the PDP-11/45 was apparently expected in the near future. Some of the -11/20's running UNIX had a KS11 Memory Protection and Relocation option to provide memory management ("the current system, which has relocation and protection hardware"(core(V))). Some also had KE11-A Extended Arithmetic Elements.

The file system is almost identical to the V6 one; the only major differences are that i) the free blocks are stored as a bit array, rather than a linked list, and ii) device 'special files' are indicated by inode numbers below 41. (not via a flag in the 'mode' word in the inode, as later).

A copy of Second Edition does not seem to be extant. TUHS has the source code for some of its user code: an early version of the first C compiler (C was just being defined at the point in time), and many commands. The 'UNIX Programmer's Manual: Second Edition' is also available.

External links