UNIX Fourth Edition

Unix V4
Type:	Multi-tasking, multi-user
Creator:	AT&T/Western Electric
Architecture:	PDP-11
Previous Version:	V3
This Version:	V4
Next Version:	V5
Date Released:	November, 1973

UNIX Fourth Edition (often referred to as UNIX V4 or V4 UNIX - 'Unix' was still normally given in all capital letters at this point in time) was an important early version of UNIX. It was the first version in which the kernel was written in C. It also had minor changes to the UNIX file system‎ (such as the ability of any inode to hold a device 'special file'), which left it in the form it retained until the BSD Fast File System.

Apparently, the only model of PDP-11 supported was the PDP-11/45.

A complete copy of Fourth Edition does not seem to be extant. TUHS has a copy of the 'UNIX Programmer's Manual' and the source for what would become the V4 kernel. The main differences in this 'nsys' kernel compared to the later V4 kernel are the earlier V3 way of registering signal handlers, and a few not yet implemented system calls. Most importantly pipes had not yet been implemented, making this kernel not fully functional even on a V3 system.

External links

• V4
  • nsys - complete kernel source
  • UNIX Programmer's Manual Fourth Edition - Introduction
  • File system
• UNIX Programmer's Manual: Fourth Edition