> If you had a 386DX then I believe you had the math copro? The 386SX did not have an FPU and needed the additional 387SX.

The 386DX/386SX distinction was the external databus (32-bit on the DX, 16-bit on the SX)

DX was “Double word eXternal", SX was “Single word eXternal”. Neither had an FPU builtin, and there were corresponding 387DX and 387SX coprocessors.

Then Intel used the same naming split (despite the abbreviations not applying) for high-end vs low-end of the 486 where the DX had a builtin FPU and the SX required a “487SX coprocessor” to get an FPU (which IIRC was internally just a 486DX processor which went into a separate “coprocessor slot” which just bypassed the “main” processor when populated.)

ah, thanks for clearing up my brain cobwebs