fabricated with FPUs. If testing showed that the CPU was OK
but the FPU was defective, the FPU's power and bus connections
were destroyed with a laser and the chip was sold cheaper as
an SX, if the FPU worked it was sold as a DX.
[Was this true of all 486SX chips?]
Some systems, e.g. Aopen 486SX, allowed a DX to be plugged
into an expansion socket. A board jumper would disable the SX
which was hard to remove because it was surface mounted.
Some SX chips only had a 16-bit wide external
data bus. The
DX has a pin to select the data bus width (16 or 32). On the
smaller SX, that line is
hard-wired to 16 inside the
package. This is similar to the 286 SX, which was a 16-bit
processor with an 8-bit external data bus.
disabled
crippleware. The German computer magazine, "c't",
They claimed that if one drilled a hole of a specified
diameter through the right point on a SX chip, this would
brake the circuit that disables the FPU. Some people actually
tried (and then bought themselves new processors).
(1997-02-14)