> It is possible to write instructions that would be 16 or more bytes, but the micro architecture will “throw” an illegal instruction exception if it encounters one. Intel doesn’t say why there’s a limit

I remember noticing on the 80286 that you could in theory have an arbitrarily long instruction, and that with the right prefixes or instructions interrupts would be disabled while the instruction was read.

I wondered what would happen if you filled an entire segment with a single repeated prefix, but never got a chance to try it. Would it wrap during decoding, treating it as an infinite length instruction and thereby lock up the system?

My guess is that implementations impose a limit to preclude any such shenanigans.