I’m interested in the journey of SysV IPC. So far I have established that these originated in CBUnix, with a lot of thinking on how to optimize these around the time that Unix 3.0/4.0/5.0 happened. They did not appear in Unix 3.0 / SysIII, and from the Unix 4.0 documentation I gather that it was not included there either.

This would make Unix 5.0 / SysV R1 the first release with what is now known as SysV IPC. The PDP11 version of R1 has the CBUnix version of shared memory, as the VAX version did not make sense in the limited address space of the PDP11.

From the pastebin summary, it would seem that IPC is not in this documentation either? That would be surprising, and reopens the possibility that IPC was part of Unix 4.0

Paul