On: What is the PDP-11 instruction set?

[gumby]

These early machines were not microcoded -- the instructions were hard coded, which tended to make the instruction sets fare more regular.

* Though later PDP-11s like the LSI-11 did have microcode -- AKA, in the argot of the time, a "writable control store"

[aap_ → gumby]

Only the first one (PDP-11/20) wasn't mircocoded. all others were.

[hazeii → gumby]

The KEF-11 for the LSI11-23 was optional, though best bought at the same time. Given the price of the chip, plugging one in tended to be a bit of a ceremonial affair.