1972 UNIX V2 “beta” resurrected from old tapes

There’s a number of backups of old DECtapes from Dennis Ritchie, which he gave to Warren Toomey in 1997. The tapes were eventually uploaded, and through analysis performed by Yufeng Gao, a lot of additional details, code, and software were recovered from them. A few days ago, Gao came back with the results from their analys of two more tapes, and on it, they found something quite special.

Here’s an update on my work with the s1/s2 tapes – I’ve managed to get a working system out of them. The s1 tape is a UNIX INIT DECtape containing the kernel, while s2 includes most of the distribution files.

The s1 kernel is, to date, the earliest machine-readable UNIX kernel, sitting between V1 and V2. It differs from the unix-jun72 kernel in the following ways:

It supports both V1 and V2 a.outs out of the box, whereas the unmodified unix-jun72 kernel supports only V1.

The core size has been increased to 16 KiB (8K words), while the unmodified unix-jun72 kernel has an 8 KiB (4K word) user core.

On the other hand, its syscall table matches that of V1 and the unix-jun72 kernel, lacking all V2 syscalls. Since it aligns with V1 in terms of syscalls, has the V2 core size and can run V2 binaries, I consider it a “V2 beta”.
↫ Yufeng Gao

Getting this recovered version to run was a bit of a challenge, and only aap’s PDP-11 emulator is capable of running it. To even get it to run in the first place, Gao had perform quite some intricate steps, but eventually he managed to build an image that can be downloaded and booted on aap’s PDP-11 emulator. The image in question, as well as some more details, can be found on the GitHub page.