> From: Jon Elson > I'm not sure the original DEC PDP-10 (KA-10) used microcode
No, it didn't; in part because it pre-dated fast, cheap ROMs (the development of which was a considerable task in the /360 project - the wonderful "IBM's 360 and Early 370 Systems" covers this is some detail). The KA10 is built out of FLIP CHIPs which carried individual transistors. Another fun KA10 fact: it used 'hardware subroutines' - i.e. a clock pulse would get to a certain point, and get conditionally diverted through some other circuitry, later to come back and continue where it left off. Whee! Noel