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That's different. Lithography masks are expensive. It's cheaper to make them once and use them for different models of the same chip than to make a separate set

That's different. Lithography masks are expensive. It's cheaper to make them once and use them for different models of the same chip than to make a separate set for each model. My understanding is that in this particular case they would sell the FPU-less version below the cost and the full one with some markup. In modern times they also do this because the process of semiconductor manufacturing is imperfect and sometimes some parts of the chip would come out damaged. IIRC this happens with GPUs a lot so they tend to have spare cores.

fredoralive 1y ago
IIRC later revisions of the 486SX have a unique mask set without the FPU, presumably the higher chips per wafer made up for the extra tooling costs. Also, as a note, unlike modern chips where they fuse off broken cores and sell them as lower specs[1] as part of the binning process, with the early 486SX the FPU was disabled before any testing / binning, so they weren’t selling broken DX dice as SXs. [1] Or in some cases, fusing if working silicon if the supply / demand curve works that way, see the infamous 3 core AMD Phenom.