Talk:Microcode

Another meaning

So the PDP-4 brochure contains what seems to be another meaning for "microcode". It says (pg. 3, in 'Extended Arithmetic Element') "adds 23 micro coded instructions". I'm pretty sure this isn't 'microcode' in the modern sense (the PDP-9 was the first microcoded DEC machine), but it means instructions where there were a number of bits, each of which controlled an independent operation (e.g. 'clear link (carry) bit'), and can be set in any combination. The PDP-8 family has a similar concept; not sure if it uses the same term (I'll check) Jnc (talk) 09:14, 12 May 2021 (CEST)

This seems to have been common DEC jargon; the PDP-8 does indeed use it, and also see e.g. INSTRUCTION MANUAL - EAE - KE09A Section 1.1. Jnc (talk) 16:15, 13 May 2021 (CEST)

I always thought this quite natural in the sense that individual bits control specific functions independently of other bits in the "microcode" field. Larsbrinkhoff (talk) 09:52, 15 May 2021 (CEST)

Oh, I agree; it is a quite natural 'extension' of the term. But it is a different meaning. Jnc (talk) 14:29, 15 May 2021 (CEST)