Instruction sets: RISC and CISC

In October 1980 David Patterson of Berkeley and David Ditzel of Bell Labs published The Case for the Reduced Instruction Set Computer. Processors of the day kept adding complex instructions, on the theory that closing the gap between machine and high-level language made programs faster. The authors argued the opposite: compilers rarely used the complex instructions, which made the hardware slower and harder to build, and a small set of simple instructions could be executed much faster.

Forty years later the argument is settled in an interesting way. Every phone runs a RISC design, ARM, and the x86 processors in most PCs still accept their complex instructions but translate them internally into simple, RISC-like operations.