On Monday, 12 September 2016 at 11:33:48 +0200, Joerg Schilling wrote: The 4.1a distribution had the initial socket interface with a prerelease of the BBN TCP/IP under it. There was wide distribution of 4.1a. The 4.1b distribution had the fast filesystem added and a more mature socket interface (notably the listen/accept model added by Sam Leffler). There was very limited distribution of 4.1b. The 4.1c distribution had the finishing touches on the socket interface and added the rename system call to the filesystem. It also added the reliable signal interface. There was very wide distribution of 4.1c as there was a 9-month delay in the distribution of 4.2BSD while DARPA, BBN, and Berkeley debated whether the prerelease of BBN's TCP/IP should be replaced with BBN's finished version. In the end the TCP/IP was not replaced as it had had so much field testing and improvement by the folks running the BSD releases that it was deemed more performant and reliable. There had been a plan to release 4.1d that would have the new virtual memory (mmap) interface, but the delay in getting out 4.2BSD caused that addition to be delayed for the 4.3BSD release. As far as the filesystem is concerned, Bill Joy had done an initial design primarily coming up with the idea of cylinder groups as a way to distribute the block and inode bitmaps across the disk in manageable size pieces. When he handed the project off to me I received a single header file that defined his prototype for the superblock and the cylinder group structures. I did all of the coding from there with Bill doing design review. My feedback from the folks at the labs was that they were not interested in incorporating the fast filesystem because it tripled the size of the filesystem code (from 400 to 1200 lines) and because it needlessly put functionality into the kernel that could be done in userland (mkdir/rmdir/rename which together were 400 of the 1200 lines of code). Kirk McKusick