What Influenced x86 ISA Evolution in Last 40+ Years
So
here’s the picture. It’s quite a high-level view, mostly focused on
early days. I am trying to formulate an extended answer on this
question: “Why does Intel IA-32 instruction encoding is so damn
complex?”The short answer is: “It’s evolution, not design”. A long
answer is, well, longer.
Three factors played their roles:
- Backwards compatibility.
- Previous projects. 8086 is different in many ways from 8080, 8008, 4004. But there were the same people behind them all.
- Competition, especially in early ages, but also throughout the XX and XXI centuries.