Nowadays, people think of just vacuum tubes and then transistors, but in the 1960s there were a lot of different technologies being used. For example, supercond

Nowadays, people think of just vacuum tubes and then transistors, but in the 1960s there were a lot of different technologies being used. For example, superconducting cryotrons, magnetic core logic, parametric-phase-locked-oscillator logic, microwave logic, electroluminescent-photoconductor logic, and tunnel diodes. If transistors didn't pan out, there were lots of other technologies that could have taken over. Magnetic core logic (not to be confused with magnetic core storage) in particular was used in several computers and seemed poised for success until advances in transistors killed it off. More: https://spectrum.ieee.org/the-vacuum-tubes-forgotten-rival https://spectrum.ieee.org/the-vacuum-tubes-forgotten-rival