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| Preface |

## Versions of UNIX

There are many different versions of UNIX. Until a few years ago, there were two main versions: the line of UNIX releases that started at AT&T (the latest is System V Release 4), and another line from the University of California at Berkeley (the latest version is BSD 4.4). Some other major commercial versions include SunOS, Solaris, SCO UNIX, AIX, HP/UX, and ULTRIX. The freely available versions include Linux and FreeBSD.

Many versions of UNIX, including System V Release 4, merge earlier AT&T releases with BSD features. The recent POSIX standard for UNIX-like operating systems defines a single interface to UNIX. Although advanced features differ among systems, you should be able to use this introductory handbook on any type of system.

UNIX can be used the way it was originally designed, on typewriter-like terminals. Most versions of UNIX can also work with window systems, which allow each user to have more than one "terminal" on a single display. Chapter 2, Using Window Systems , shows the basics of a window system. All other chapters are for every UNIX user - with or without a window system.

The UNIX Operating System |  | What This Handbook Covers