Yep. The 486SX was the 486 with disconnected math processors that failed quality control. The coprocessor "487" upgrade chip was simply a fully working pin incompatible (only fit in the upgrade slot) 486.

On the 386 line, the SX/DX distinction was the equivalent of the 8088/8086 distinction for data bus width (NOTE: the 8086 was the wider processor, the cheaper 8088 was in the IBM PC).

Yeah, I meant the 486sx, but the little grey cells were not up to snuff when posting that apparently.

I got a fair amount of grief about not having a math co-processor due to some programming friends and I were doing at the time.

That said, those were the formative days where getting dirty and playing with your machine (building your own rig) started for me. I've since given that up since most machines are fast enough these days for my uses.