“it cannot have an FPU added (that is not the case with Cyrix 486S…)”
This is mostly true but the 486SX can be paired with a math coprocessor via the 487SX, but the 487SX is actually a full CPU that disables the SX, not a full FPU!
The point is still very valid. You can't add a math coprocessor to the 486SX.
The 487SX is nothing more than a polite fiction to allow consumers (and the computer shops selling to them) to continue their existing habits of buying FPU-less systems, (because most people didn't need FPUs) safe in the knowledge they could buy the upgrade if they ever needed it.
It actually cost the motherboard vendors quite a bit more to wire up the second socket, so obviously there was demand for the flexibility.
“it cannot have an FPU added (that is not the case with Cyrix 486S…)”
This is mostly true but the 486SX can be paired with a math coprocessor via the 487SX, but the 487SX is actually a full CPU that disables the SX, not a full FPU!
The 487SX is nothing more than a polite fiction to allow consumers (and the computer shops selling to them) to continue their existing habits of buying FPU-less systems, (because most people didn't need FPUs) safe in the knowledge they could buy the upgrade if they ever needed it.
It actually cost the motherboard vendors quite a bit more to wire up the second socket, so obviously there was demand for the flexibility.