From: Jon Elson
I'm not sure the original DEC PDP-10 (KA-10) used
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!