The Intel (and AMD) x86 manuals strongly hint at the octalness of the encoding, but don't explicitly mention it; I seem to remember some of the documentation for the 8080/8085 did summarise the instructions in octal, since they were also encoded similarly:

http://www.righto.com/2013/02/8085-instruction-set-octal-tab...

http://www.z80.info/decoding.htm

But although frequently described as irregular, the encoding of the x86 and its predecessors are still far more regular than something like a VAX:

https://www.cs.auckland.ac.nz/references/macvax/op-codes/VAX...

This kind of summary is useful for students (like me) who're taking computer systems courses and have been taught in MIPS but want to get a primer into x86.

Interesting, explaining the encoding of x86 opcodes (opcodes encoded in octal, addressing modes, etc.).

how do octals compare to bytes and today's machines ?