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Unix V4 Update

Posted on 2025-12-24 by jcs

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.

This entry was posted in General and tagged Tech, Unix. Bookmark the
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