A month and a half ago, I wrote about the discovery of an original Unix V4 tape in a storeroom at the University of Utah. V4 was special because it was the first version of Unix to be largely written in C rather than PDP-11 assembly language. Until the discovery of the tape at the University of Utah, it was believed that Unix V4 had been lost except for parts of its manual.
At the time of the discovery it was uncertain if the tape could even be read. Magnetic tape is famously volatile and it had been sitting in an uncontrolled environment for years. Nevertheless the experts at the Computer History Museum were able to read the tape except for a couple of damaged blocks that they were able to reconstruct and verify correct with the CRC.
Hobbyists who care about old systems and Unix history have even been able to boot the system on a PDP-11 emulator. Diomidis Spinellis who maintains a git repository of Unix source code has a blog post about the V4 discovery and how it fits in with the larger Unix corpus.
That’s not a straightforward as you might think because there weren’t really any software version releases. Rather the version numbers refer to the manuals. The actual software that a recipient got was just what happened to be on the (sole) Unix research computer at the time the tape was cut and it was given the version number of the last manual.
You can read Spinellis’ estimate of where the software on the tape fits into the larger body of Unix code on his blog. For those who care about Unix history, this is a major find and a reason for celebration.