The history of Unix on the PC: Exploring lesser-known variants

This tip explores the history of Unix, from its creation by AT&T in the 1960s to its present-day use on x86 hardware and PC-compatible systems. Brush up on your Unix history and learn about Unix variants that you never knew existed.

When someone discusses the Unix operating system on a PC, many modern computer users think of Linux, a Unix work-alike...

first released by Linus Torvalds in 1991. Linux is a relative newcomer to the field; Unix and Unix-like operating systems have been released for Intel x86-based systems as far back as 1979. This article covers some lesser-known Unix variants for IBM PC-compatible systems, both those that survive today and the ones that were not long-lived or commercially successful.

Creation of Unix
Unix started in 1969 as an AT&T Bell Labs research project. Lab employees Ken Thompson and Dennis Ritchie (creators of the C programming language) wanted a smaller-scale version of the Multics OS previously developed by Bell Labs, MIT and General Electric. The result was Unix, written in assembly language on a DEC PDP-11/70. The name was coined as a wordplay on Multics.

Because of an earlier antitrust decree, AT&T was forbidden from entering the computer business. Unix was made available under license to universities, commercial companies and the U.S. government. As more of the OS was made portable and rewritten in C, ports to a wide variety of computer systems were made available. In 1979, Bell Labs released its last edition of Research Unix, Version 7.

The origin of BSD
At the same time, the University of California's Computer Systems Research Group had its own set of patches and enhancements to Version 6 Unix. This was known as 1BSD, the first Berkeley Software Distribution. By 1983, 2.9BSD was released and was the first version to be a complete OS (based on V7 Unix) rather than patches and enhancements to a separate distribution.

AT&T followed up Version 7 with Unix System III, which was made available for commercial use starting in 1982. Eventually, System III was combined with some features from BSD to create System V Release 1. Most modern Unix distributions, derivatives or workalikes are based on System V, BSD or a combination of the two.

Unix on a PC
In 1983, the Mark Williams Company of Chicago released Coherent, the first Unix-like system for IBM PC-compatible computers. A clone of V7 Unix (having no AT&T or BSD source code), it was originally written for Digital Equipment Corp.'s PDP-11 series of machines, then ported to PC compatibles. Coherent was popular for its low price of $99 and praised for the high quality of its documentation. It continued to be upgraded until version 4 in 1994, and Mark Williams Company ceased operations in 1995.

The next major implementation of Unix for PC-compatible systems came from Microsoft, which was still in the business of providing programming languages and operating systems for other companies. After purchasing a Unix license in 1979, Microsoft made its port, called Xenix, available on 16-bit systems. The first port of Xenix (based on V7 Unix) was to Digital Equipment Corp.'s PDP-11 systems. Ports based on Unix System III were released for Altos, Tandy 6000 and the Apple Lisa. In September 1983, The Santa Cruz Operation (SCO) released its port of Xenix for the IBM PC. Xenix version 2.0 (1985) for the PC was based on Unix System V.

In 1987, Microsoft transferred ownership of Xenix to SCO, which continued to develop and market the System V-based product as "SCO Unix" (later SCO OpenServer). Some features from SCO Unix were released as part of the feature set of AT&T's System V Release 4, which was jointly developed by AT&T and Sun Microsystems. In 1995, SCO acquired ownership of the UnixWare products from Univel, a joint partnership between AT&T's Unix System Labs and Novell. Due to its stability and commercial support offerings, SCO's OpenServer product was -- and still is -- used by a large number of commercial clients and companies, including McDonalds, Yum! Brands, NASDAQ and the Toronto Stock Exchange.

The original Santa Cruz Operation eventually renamed itself Tarantella and sold all rights to its Unix products to Caldera in 2001. Caldera renamed itself The SCO Group, and starting in 2003 it filed lawsuits against many Linux vendors and users, claiming that source code in the Linux kernel was stolen from Unix. As of 2010, the courts have proven these allegations false and The SCO Group has filed for Chapter 11 bankruptcy protection.

While many people are familiar with Sun Microsystems' Solaris x86 Unix for Intel-based hardware, they may not be aware that Solaris is the second Unix sold by the company for mainstream PCs. In 1985, Interactive Systems Corporation ported AT&T System V Release 3 and released it as 386/ix. In 1992, Sun bought ISC from Kodak and continued releasing Interactive Unix under its own brand until 2001. Interactive Unix was sold at the same time as Solaris x86 for seven years; the last release was "System V/386 Release 3.2 Version 4.1.1" in July 1998. Support for the product was finally dropped in 2006. Interactive Unix's sales and support longevity can be attributed to a high number of installations for embedded and automation applications.

Not all PC Unix releases were based on System III or System V. In 1992, Lynne and William Jolitz released 386BSD, a port of the 4.3BSD Net/2 codebase to PC-compatible computer systems using the Intel 80386 CPU. In 1993, a difference of opinions on the future direction of the project between the Jolitzes and other contributors led to the creation of two different BSD-based operating system efforts -- FreeBSD (geared primarily towards x86 systems) and NetBSD. In 1995, the OpenBSD project was itself forked off from NetBSD, and focuses on system security. The latest stable release of 386BSD was version 1.0 in 1994.

The FreeBSD, NetBSD and OpenBSD projects are highly active to the current day, and are the primary choices for someone who wants to run a "real Unix" on x86 hardware. The Darwin core of Apple's Mac OS X operating system is a combination of code from FreeBSD along with features from NeXTStep. Mac OS X is the second most popular general-purpose operating system in use for the Internet and is the most successful Unix-like desktop OS on the Internet as of 2009.

In 1991, members of the Berkeley CSRG formed a company called Berkeley Software Design Inc. in order to develop and sell a proprietary version of BSD Unix for PC-compatible systems. Some of the porting was based on work by Bill Jolitz. The initial release of version 1.0 came in March 1993. This OS, called BSD/OS, BSD/386 or sometimes BSDi, was a much cheaper alternative at $995 (for a license with binaries and source code) than a source code license for AT&T System V Unix. At the time, a binary distribution of System V could cost less than $200, but a source code license was more than $100,000. BSD/OS was relatively successful in the market for server operating systems, but gradually lost share to the open source BSD releases and Linux, finally being sold to Wind River Systems in 2001.

Minix is a Unix-like microkernel-based operating system. First released in 1987, it was created by Andrew S. Tanenbaum for research and educational purposes and to accompany his textbook Operating System Design and Implementation. Linus Torvalds' Linux kernel was inspired by the design of Minix, and initial Linux development was done on a Minix system. Torvalds has famously said, "If 386BSD had been available when I started on Linux, Linux would probably never have happened." Minix continues to be updated and is currently at version 3.

This has been a general history of Unix on PC-compatible systems, with an insight into the releases and distributions that many people may have never heard of. It is certainly not comprehensive coverage of the subject; much more information and entire books are available.

ABOUT THE AUTHOR: Bill Bradford is the creator and maintainer of SunHELP and lives in Houston, Texas.

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