True, but SX used to stand (officially? dunno) for Singleword Xchange, as it had a 16 bit bus. DX was Doubleword Xchange, hence 32bit bus.

Then in the 486, the bus was always 32-bit (at least from Intel. I have a faint memory of Cyrix 486SLCs with a 16bit bus), and now the SX-DX indicated the presence of an integrated FPU instead.

Bonus: the 80487 was not just an FPU. It was a full 486DX which just disabled the main CPU and did all the work, and of course had an FPU.

Others have mostly answered it.

As a 486DX owner (IBM PC compatible AST Advantage), I was aware of the lower price point 486SX chip, and the difference was that the latter did not have hardware support for floating point calculations. In marketing jargon, the 486DX had an "integrated math co-processor."

I was also aware of the previous generation also using DX/SX designations, and until recently, assumed that the SX designation also meant a lack of a math co-processor, when instead, it simply meant a 16-bit data bus, compared to the 32bit data bus of the DX chip, and that neither DX or SX variant of the 386 had dedicated hardware for floating point calculations.

I was also confused by this statement and had to refresh my memories. In short, 386sx had 16/24 bus instead of 32, which made it 286 main board compatible. 486sx was simply non-fpu version.

and then they released DX4 that quite logically ran at .. triple the bus speed