There are two different cases: i) support of split I+D in the kernel, and ii) support of split I+D in user processes. Both arrived with V6; the V5 source: https://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/sys/conf/mch.s https://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/sys/ken/main.c (former for kernel; later for users) shows no sign of it. You are wrong. The chief differences between the KB11-A&-D of the -11/45 and the -B&-C of the -11/70 were i) the latter had a cache, and ii) the latter used the 32-bit wide Main Memory Bus, which also allowed up to 4 Mbytes of main memory. Detail here: https://gunkies.org/wiki/PDP-11/70 along with a couple of lesser differences. I think you meant for code, data, and user block. The /50 and /55 had the identical KB11-A&-D of the /45; the difference was that they came pre-configured with Fastbus memory. No; the F-11 processors did not support I&D, the J-11 did. Noel