2 ms·
> The issue with x86 is that instructions can be any length, and that their length is a nontrivial function of their encoding. x86 is an old design, but why di
by blackrock 6y ago
> The issue with x86 is that instructions can be any length, and that their length is a nontrivial function of their encoding.
x86 is an old design, but why did Intel design it this way?
- Veedrac 6y agoEarly on the focus was on the hypothetical CISC advantage, hence wanting ‘compressed’ variable-length instructions, even though the ISA hasn't ended up especially space efficient now that the actual complex stuff is legacy. But as to why their encoding is so difficult, put that down to lack of foresight. x86 was designed before parallel decode became a thing, and the complexity accumulated over time. Intel have had quite a few ISAs and all the famous ones are bad, so there doesn't have to be a good reason beyond that.