“In brief, the microcode in the 8086 consists of 512 micro-instructions, each 21 bits wide.”
The chip every modern PC still descends from ran on 512 micro-instructions. Intel crammed them into a 128 by 84 array with 1978 tooling. Ken Shirriff pulled all of it out of die photos. This is the kind of work Intel would never document, and it took one guy with a microscope to do it.