CPUs without microcode exist. While microcode isn't exactly a new innovation, ea...

shawnz · on Nov 10, 2018

Right, but it wouldn't be possible for a modern CPU (for example: how would you retain compatibility with older architectures? how would you patch it if you find a critical bug in an instruction?)

Furthermore the parent was asking about having no microcode running on the CPU which is what I was speaking to. A CPU designed to use microcode can't be run without microcode. But yes, it is of course possible to design the CPU to not use microcode in the first place.

pjmlp · on Nov 10, 2018

Microcode free CPUs was mostly a RISC thing, and basic CPUs like Z80 and 6502, almost everyone else always had some form of microcode in them.

shakna · on Nov 10, 2018

> CPUs without microcode exist. While microcode isn't exactly a new innovation, early mass-market CPUs were not implemented that way.

> Microcode free CPUs was mostly a RISC thing, and basic CPUs like Z80 and 6502

Those quotes aren't incompatible - the 6502 and Z80 are core to the early mass-market computer movement.

So whilst microcode-free may be rare now, there was a time when it was the norm.

pjmlp · on Nov 10, 2018

The norm in the context of 8 bit home micros.