intel 486sx

Intel 486SX
486SX

   <processor> An {Intel 486DX} {microprocessor} with its
   {floating-point unit} disconnected.  All 486SX chips were
   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.

   The {Jargon File} claimed that the SX was deliberately
   disabled {crippleware}.  The German computer magazine, "c't",
   made this same theory the basis of an {April Fools Joke}.
   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)