Oh, all those machines used linear ECL (Emitter Coupled Logic) circuits for speed. Terribly hot logic family but complimentary FET based devices just couldn't yet cut the mustard.
FWIW, the transition from the Model 155 to the 157 heralded the introduction of table driven virtual memory. We called it "relocation" hardware then. :-)
The first engineering model of the 155 used core memory but transistor memory became fast, reliable and cheap enough during its development that a very disruptive re-design was performed across the whole family of machines.
That was my first job out of the university and what fun it was! And what an incredible experience working for IBM was then.
What a fun gig. And what interesting times. I remember the headlines in Computerworld when the cost of a megabyte of memory had dropped to $15,000.
I did very little work on the mainframes, lots on the IBM 1800, a process control computer, and my first consulting gig was on a system 32. Don't ask me what programming language it was.
It was all discrete, hard logic circuits centered around a unit called the scoreboard. That term was borrowed from either Burroughs or CDC, I can't remember which. That machine pioneered many of the scalar optimizations that are common in today's architectures.
