Many thanks for the below notes! Some comments in line below: Looking at the organisation of the source tree I’d say it is more likely that the base was V32 with bits of 4.1BSD imported than the other way around. If it was the other way around somebody would have spent considerable time to reorganise the source tree back to a form consistent with 32V. I think that such an effort would have been remembered even 40 years later. I don’t mean disrespect, but I think the surviving sources support Rob’s recollection that it was a gradual, ongoing effort. As a first approximation looking at the top comments of a file gives its origin: the BSD derived files still have an SCCS-type marker. For example the file https://www.tuhs.org/cgi-bin/utree.pl?file=V8/usr/sys/sys/vmmem.c still has the top comment "/* vmmem.c 4.7 81/07/09 */“, even though it was last touched in 1985. (By the way, who knows which tool generated these comments? Is it early SCCS?) For the VM code, the BSD version stamp comment strings are consistent with the 4.1BSD release. For the TCP/IP stack they are consistent with 4.2BSD; it would seem probable to me that this code was imported multiple times during the development of 8th Edition. As far as I can tell 4.1aBSD was released in March or April 1982. Unfortunately no source code tape of it has surfaced, and SCCS coverage at this point is still very partial. I think 4.1b with the initial FFS implementation followed late summer 1982, I don’t have a more precise date (yet). Thank you for pointing this out. With my focus on networking I had completely missed that. For those interested, some of the relevant files are: https://www.tuhs.org/cgi-bin/utree.pl?file=V8/usr/sys/h/param.h (middle bit) https://www.tuhs.org/cgi-bin/utree.pl?file=V8/usr/sys/h/filsys.h (note the union) https://www.tuhs.org/cgi-bin/utree.pl?file=V8/usr/sys/sys/alloc.c (note 'if(BITFS(dev))’) And indeed the bitmap was fitted inside the 4KB superblock,