Chapter 1. Introduction

The Unix operating system originated at AT&T Bell Labs in the early 1970s. System V Release 4 (SVR4) came from USL (Unix System Laboratories) in the late 1980s. Unix source ownership is currently a matter of litigation in U.S. courts. Because Unix was able to run on different hardware from different vendors, developers were encouraged to modify Unix and distribute it as their own value-added version. Separate Unix traditions evolved as a result: USL's System V, the Berkeley Software Distribution (BSD, from the University of California, Berkeley), Xenix, etc.

SVR4, which was developed jointly by USL (then a division of AT&T) and Sun Microsystems, merged features from BSD and SVR3. This added about two dozen BSD commands (plus some new SVR4 commands) to the basic Unix command set. In addition, SVR4 provided a BSD Compatibility Package, a kind of "second string" command group. This package included some of the most fundamental BSD commands, and its purpose was to help users of BSD-derived systems make the transition to SVR4.