So basically you were thinking 486SX -- where the on-chip numeric coprocessor was disabled. Ostensibly the 486SX came about as a means for Intel to sell 486 that had non-working numeric coprocessor component (i.e. only the on-chip numeric coprocessor failed test -- otherwise it was an operating 486). I myself saw opting for 486SX over 486DX as not being very meaningful -- why opt for something that has been "dumbed down" on purpose (same reason why I saw little point in 386SX) ?

One thing that I also saw with the 386SX -- problems when adding numeric coprocessor upgrade. Since the motherboard was for 286, then you'd have to install the 287 chip -- which would likely be clocked slower than what your 386SX (so you end up having to "underclock" the CPU -- i.e. run at slower speed -- to make it work). I know a few people who discovered that after installing the 287 nomeric coprocessor made their system run *slower* (we confirmed that w/o the coprocessor installed and program compiled with x87 softwre emulator library ran *faster* than with same program recompiled for x87 and run on system wih 287 installed).

Speaking of clocking issues... Remember the headaches of matching speeds for VL-bus stuff? Or the reason why 50MHz 486DX2 was not always faster than 33MHz 486DX... Of course what was irritating was when you had a relatively rare 50MHz 486DX -- trying to find matching VL-bus component was a pain (as they were *really* rare).

>I may be misremembering then - it was the disabling of the math co-processor I was thinking of. Just remember the concept of dumbing down a chip for marketing reasons.
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>>>Anybody remember the 386sx? A firmware upgrade would have been kind of cool.
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>>The main problem I saw with the 386SX was that it was made to be pin-compatible with the 286 -- which usually meant that systems built with it are likely to be "held back" by the motherboard and associated hardware (i.e. basically you couldn't expand beyond 286 capabilities in terms of memory and associated operation modes.). Of course it's not too different from 8088 (in that it was basically a 16-bit 8086 sitting on an 8-bit bus)...
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>>And then there was the 80486SX... where it was essentially a 80486 with built-in numeric co-processor disabled. You could upgrade to get the numeric coprocessor by installing a 487 -- which was not just the coprocessor but a complete 486. However, you didn't end up with two 486s -- as the installation of the 487SX would disable the 486...