Relay: binary representation. Valve: faster but hotter.
Transistor: importance of move to semi-conductors.
Integrated circuits: SSI (small-scale integration, MSI, LSI upwards; regular structures move ahead: memories. Simple processors, short word width (early Intel chips). Processor on a chip: specialised applications only.
Continued push for complexity in fabrication encouraged designers to produce complicated processors. In due course, this producedf the RISC backlash as designers realised that simple, well-designed chips, with carefully-designed compilers, could perform better than highly complex chips for which effective compilers were scarce.
Today: compiler writing tie-in: instruction sets matched to compilers are arguably being replaced with compilers matched to (reduced) instruction sets. More and more software between the user and the application encourages the push for performance, as well as raw power for scientific computation.
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