Researchers from the University of Utah have found a piece of computing history, previously thought lost, languishing in a dusty corner of a storage room: a magnetic tape containing the only known remaining full copy of the UNIX V4 operating system.

“While cleaning a storage room, our staff found this tape containing UNIX V4 from Bell Labs, circa 1973,” Rob Ricci, research professor at the University of Utah’s Kahlert School of Computing and director of the Flux Research Group, explained of the discovery. “Apparently no other complete copies are known to exist.”

A tape containing the only surviving complete copy of UNIX V4 by Ken Thompson and Dennis Ritchie has been found in a Utah storeroom. (📷: Public Domain)

UNIX V4, more formally known as UNIX Fourth Edition, was the first in the family of operating systems — a project launched by AT&T Bell Labs researchers Ken Thompson, Dennis Ritchie, Doug McIlroy, and Joe Ossanna, as, originally, the Uniplexed Information and Computing Service (Unics) in reference to the Mutiplexed Information and Computer Services (Multics) time-sharing system with which they had become disillusioned. It’s notable as being the first version to have been rewritten in C, making it more portable than the assembly-language V3 and earlier, but the presence of various routines specific to the Digital PDP-11 minicomputer meant UNIX, as it became known, wouldn’t boot on a non-DEC machine until the release of V6 in 1977.

UNIX’s place in the history of computing, both as a platform in its own right and as inspiration for projects including Linus Torvalds’ Linux, cannot be overstated. Its success was primarily down to the decision to openly release its source code — which, in turned, stemmed from a 1956 court’s declaration that AT&T was forbidden from entering the computer business, a ban that would stand until 1984 and the divesture of its regional operating companies that freed AT&T to release UNIX as a commercial closed-source product. This, in turn, inspired the foundation of the GNU Project — named for the backronym “GNU’s Not Unix” — the Free Software Foundation and the creation of the reciprocal “copyleft” GNU General Public License.

To say UNIX was influential is no understatement. (📷: Eraserhead1, Infinity0, Sav_vas CC-BY-SA 3.0.)

Despite having been distributed freely, copies of the earliest UNIX releases are hard to find — at least in fully-working form. The technology of the time meant storing the software on bulky reel-to-reel magnetic tapes, many of which were overwritten and eventually discarded. Partial copies of UNIX V4 exist, but Ricci’s discovery is the first that promises a fully complete version of the operating system — which would be executable on original PDP-11 and compatible hardware or in emulation on a more modern system.

“It probably spent most of its life sitting in my former advisor Jay Lepreau’s office, whose handwriting is on the label,” Ricci says of the spooled tape. “We’ve only had this specific storage space for like a decade. But yeah[,] we don’t know where it came from originally.”

The tape is in the process of being transferred to the Computer History Museum, where efforts will be made to image the software and make it openly available to all. More information is available in Ricci’s Mastodon thread.

Gareth Halfacree

Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.