The only "coprocessor" was the math coprocessor, and *ALL* 386 chips could have one of those added. You did *not* upgrade an SX to a DX by adding one. The difference between SX and DX was the number of address lines, and you can't change that by adding an extra chip.
Now, the 486SX chip had no math coprocessor, and all 486DXes did (though as you point out, there were several clock multipliers). And the "math coprocessor" for the 486SX was really just a 486DX, which disabled the main chip. That was the only SX -> DX upgrade that you could *do*, let alone that involved a coprocessor.
(I should know on the 386 chips: I had a 386DX-33 that got a math coprocessor added about a year later. It was *never* an SX.) |
