24 Jan
2013
24 Jan
'13
1:50 p.m.
On Jan 24, 2013, at 3:45 PM, Dan Gahlinger <dgahling at hotmail.com> wrote:
Nope,I remember running this software, it was from the above-board peopleI think it was
called above486 and it would re-enable the math coprocessor.
in previous versions of the above board (386) you needed the hardware version.
Bear in mind that Intel had some seriously schizophrenic taxonomy
regarding "SX" vs. "DX". In the 386, the SX part was simply a
386 with a 16-bit bus, while the DX had a 32-bit bus (I'm told
they stood for "Singleword eXternal" and "Doubleword eXternal",
respectively, though I wouldn't be surprised if that's made up).
The 386 never had a built-in FPU; any 386 machine with an FPU was
a machine with a physical 387 (SX or DX, as appropriate).
The 486SX was every bit as much a 32-bit bus chip as the 486DX,
but the on-die FPU was disabled (whether via laser or a blown
fuse, ultimately it's probably just an enable line that was left
floating by hook or by crook). I agree with Ethan that they may
have diverged into two separate masks towards the end of the life
of the CPU, but you would need an awful lot of market demand for
that to happen (enough for the cost of another mask to be
eclipsed by the savings in die space).
- Dave