52 years later, only known copy of Unix v4 recovered from randomly found tape, now up and running on a system — first OS version with kernel and core utilities written in C

There's probably more than a handful of Unix lovers among the TH audience, and today's tale is a Christmas gift that should warm many a cold sysadmin's heart. The University of Utah's School of Computing found and recovered a magnetic tape with the only known copy of Unix v4, the first version of the operating system with both its kernel and core utilities written in that shiny newfangled language known as C.

The recovery process was carefully executed, but the results were "easy" as these things go. The nine-track 3M tape is from 1973, making it over 50 years old, and had "a pretty good chance of being recoverable." That was a fair assessment by archivist Al Kossow of Bitsavers, who did the actual recovery by "taping off the head read amplifier, using a multi-channel high speed analog to digital converter which dumps into 100-ish gigabytes of RAM, then [the readtape] analysis program Len Shustek wrote."

The actual data is around 40 MB and is available for download with a README of instructions for actually running the operating system, though it's not a one-click affair. You'll need to have an initial boot environment and then compile parts of the operating system, as that was the fashion back then. Unix v4 required a then-fancy DEC PDP-11 minicomputer, which can handily be emulated using the SimH software. More casual observers can instead look at a screenshot of the operating system running under Irix.

The recovery process took an entire team, and the bulk of the work was apparently researching old, poorly documented history. Unix was a passion project created by a small group of programmers, and at the time of the v4 release, it was still an escaped lab experiment. Records indicate the recovered tape was received by none other than Martin Newell, who designed the original version of the famous teapot that's become a staple of 3D software around the world.

Interested readers can check out the entire thread about the recovery, and possibly marvel at the comments in the C code. The famous code comment "you are not expected to understand this" is included therein.

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