40 Years of UNIX, and ‘The Scariest Thing I’ve Ever Done’


Let’s take a moment to appreciate the heritage of this influential operating system, and the many ways it has bettered our world.

On a beautiful October morning in 1973, Ken Thompson and Dennis Ritchie drove up the Hudson River valley to the new T.J. Watson Research Lab of IBM. They were to deliver the first paper about Unix, the operating system they had invented and developed at AT&T Bell Labs in Murray Hill, N.J., at the Symposium on Operating Systems Principles.

It was Ken who actually delivered the paper to an audience of about 200.

“So what?” you ask. “I don’t use Unix!”

Well, you may not be aware of it, but to a great extent, you do.

You are reading this article online, and the Internet runs on Unix. If you run Linux or Mac OS X, the line is clear and distinct. If you use BSD, it is today’s Unix. Android is derived from Linux. And if you use Windows, your memory cache and your networking stack are drawn from Berkeley Unix.

What Ken and Dennis (and some of their colleagues) brought to the public in 1973 soon revolutionized computing. Many of those in the audience returned to their home institutions determined to get a copy of the new system.

The paper was one of five published in the July 1974 issue of Communications of the ACM. But the interest was such that months before that Lou Katz and Reidar Bornholdt had convened a meeting at Columbia University’s College of Physicians and Surgeons (on Wednesday, 15 May 1974). Two dozen people from a dozen institutions listened to Ken Thompson in the Merritt Conference Room.


At the outset of their paper, Ritchie and Thompson listed six features their system offered:

  1. A hierarchical file system incorporating demountable volumes
  2. Compatible file, device and inter-process I/O
  3. The ability to initiate asynchronous processes
  4. System command language selectable on a per-user basis
  5. Over 100 subsystems including a dozen languages
  6. A high degree of portability

Twenty years later, I listed “a few things that I like about Unix.” They were:

  1. Available on a number of platforms
  2. multiuser
  3. provides a directory hierarchy
  4.  shares computer resources sensibly
  5. supports manipulation of files, processes, and programs
  6. allows inter-process and inter-machine communication; and
  7. permits access to its operating features.

But let’s look at how Unix gave rise to nearly everything else we use today.

One thing to keep in mind is that “software licensing,” the bugbear of the 80s, 90s and today, didn’t really exist in the 1970s. Though there were requests for the Unix software following the 1973 paper, software was conveyed royalty-free under simple letter agreements. (The original agreement between Western Electric and the Regents of the University of California for Unix Version 5 ran to six pages, two of which were the title page [unnumbered] and the signature page. Page 5 was the “Definitions Appendix.” The language would have been intelligible to any high school graduate. It was “Effective as of December 1, 1973.”)

Initially, the procedure was quite simple: An institution sent an RK05 DECpack (a removable media hard drive with a total capacity of 1.6 million 12-bit words) to Ken and he sent one back with the bits on it. When the chore became too much for Ken, it was turned over to Irma Biren; you sent one or two RK05s to Irma with a UPS return label and got back DECpacks or tapes with bits on them.

One of the attendees at SOSP in 1973 was Cyrus Levinthal, chairman of Biological Sciences at Columbia University. “Cy got RK05s for the Department,” Lou Katz told me, “But we didn’t have a drive. So I drove down to Murray Hill and Ken cut me a 9-track tape.” Great service.

Five years later, it was Bill Joy (who was to become one of the founders of Sun Microsystems) who created the Berkeley Software Distribution, BSD. The first tape contained the Unix Pascal System and the Ex text editor. “The distribution is a standard ‘tp’ format, 800 bpi magnetic tape. A 1200 foot reel is the minimum and preferred size.” It cost $50. Bill sent out about 30 tapes of BSD in 1978.

Andrew S. Tanenbaum of the Free University in Amsterdam soon began work on his clone, MINIX (Mini-UNIX), which was and still is free, small, flexible, secure, and based on a micro-kernel. It was MINIX that Linus Torvalds was running when he created (first) a terminal-emulator and then, in 1991, Linux.

At the same time, the Computer Systems Research Group at UC Berkeley continued development of UNIX. In June 1986, version 4.3 was released (in 2006, Information Week called 4.3BSD “the greatest software ever written”).

But in 1990, AT&T’s Unix Systems Labs sued the University of California and, for two years, development ceased. Linux effectively filled a void.

The suit was settled (in Berkeley’s favor) in 1994. OpenBSD, NetBSD, FreeBSD, and DragonFly BSD have been released since then. More importantly, all the BSDs have been released under a very permissive Berkeley license.

The result has been great proliferation of Unix code. Microsoft Windows has used BSD-derived code in its implementation of TCP/IP and it bundles recompiled versions of BSD’s command-line networking tools since Windows 2000. (In the first edition of The Road Ahead [November 1995], Bill Gates largely dismissed the Internet (mentioning it briefly) and the Web. When he realized that the Internet was moving ahead, his strategy was revised and a new edition of The Road Ahead came out in October 1996.)

Darwin, the system on which Apple’s OS X is based, is derived from 4.4BSD and FreeBSD.

Finally, Android, Google’s operating system for touchscreens and other devices, is directly descended from Linux.

But, as I wrote at the outset of this historical note, you’re reading this via the Internet. And the Internet runs on Unix. This is thanks, in part, to Steve Holmgren, then a graduate student at the University of Illinois, who published “NETWORK UNIX” on May 14, 1975 (RFC 681). He was publicizing Unix on the ARPAnet. In actuality, he effectively put the Net onto Unix.

Raise your cup or glass to Ken and Dennis, who delivered that paper 40 years ago. “The scariest thing I’ve ever done,” Ken told me.

Note: If you are interested, my A Quarter Century of UNIX (1994) and Casting the Net (1995) are available from Amazon; as is my The Daemon, the Gnu and the Penguin (2008). See also: UNIX Methods and Concepts: Putting the Genie Back in the Bottle.

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  1. Amgad Suliman says:

    Great article.

  2. But what about the OS that the original unix was a pale reflection of? i.e. Multics, arguably the best OS ever.

    Multics played a significant role in the creation of unix, as any proper history of unix would point out.

    Sorry, if you were one of my students you’d maybe get a C or C+ for this.

  3. Thanks to drgb for also remembering Multix. As I read through the list of what unix has and does, I kept thinking about how Multix did that, and that, and that, and that … And was more secure. Where is Multix? Since it was proprietary, and owned by one company, eventually, nobody was motivated to port it. Only recently has a version of the Multics source code, written in PL/I been released. But all the unices owe many of their features to Multix.

  4. Steve Blackburn says:

    A nice thread to this story that was skipped over is the Lions Book. Look it up.

  5. Roger Browne says:

    Steve, it’s a bit mean to mention the Lions book without telling people about it. I was fortunate to study Computer Science at UNSW under John Lions. One of the subjects was “Operating Systems”, for which the textbook was his “annotated guide to the Unix source code”. The course consisted primarily of reading and understanding the Unix source code, with a bit of help from his book. The source code, back then, was concise and elegant. It had to be concise because we ran it on a PDP-11 with 64 kilobytes of RAM. Later we ran it on some VAX 11/780s with 256kB RAM. The DEC engineer couldn’t believe that Unix on an 11/780 was fast and responsive when timesharing 32 students who were compiling Pascal programs using DECWriter hardcopy terminals. The same machine running DEC’s own VMS operating system could only support eight simultaneous users.

  6. Excellent, what a blog it is! This webpage provides useful data to us,
    keep it up.

  7. It’s true that many people have used some application that is supported or derived from Unix. Many businesses use terminal emulation for their workstations, which relies heavily on Unix or Linix. It can be very advantageous for businesses to enable employees to use any workstation or device to access their files and programs. Thanks for the history lesson about how Unix has impacted so many lives and industries. Thanks.

  8. just the best!

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