I met Gene Amdahl once, when I took a summer course in computer architecture at UCSC.  We got a tour of the Amdahl plant. They had a huge prototype CPU built out of TTL, which they built before making custom ICs.  Each board in the prototype became one IC.  Each row of cards in the prototype became one board.  Each rack became one row of cards.  That was how you debugged hardware designs in 1975.