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 for Intel 486SX
From The Free On-line Dictionary of Computing (30 December 2018) :

  Intel 486SX
      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).

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