Some minor nitpicks, but hey, we're counting registers, it's already quite nitpicky :)
Add far as I van remember, you can't access the high/low 8 bits of si, di, sp. ip isn't accessible directly at all.
The ancestry of x86 can actually be traced back to 8 bit cpus - the high/low bits of registers are remenants of an even older arch - but I'm not sure about that from the top of my head.
I think most of the "weird" choices mentioned there boil down to limitations that seem absurd right now, but were real constraints - x87 stack can probably traced back to exposing minimal interface to the host processor - 1 register instead of 8 can save quite a few data line - although a multiplexer can probably solve this - so just a wild guess.
MMX probably reused the register file of x87 to save die space.
Add far as I van remember, you can't access the high/low 8 bits of si, di, sp. ip isn't accessible directly at all.
The ancestry of x86 can actually be traced back to 8 bit cpus - the high/low bits of registers are remenants of an even older arch - but I'm not sure about that from the top of my head.
I think most of the "weird" choices mentioned there boil down to limitations that seem absurd right now, but were real constraints - x87 stack can probably traced back to exposing minimal interface to the host processor - 1 register instead of 8 can save quite a few data line - although a multiplexer can probably solve this - so just a wild guess. MMX probably reused the register file of x87 to save die space.