Comment by renox

> but all MIPS instructions are 4 bytes.

Like ARM, MIPS has also 16 bit extensions, two in fact: MIPS16 and microMIPS.

> [cut] thus I believe small variable-length encodings (like x86) are ultimately better since they allow for better utilisation of cache

I disagree: mixed 16/32 bit RISCs ISA have nearly the same code density as x86 and are far simpler to decode.

So beside software compatibility (the killer feature) (well except for Intel of course), the x86 ISA has NO advantage.