The Free On-line Dictionary of Computing (30 December 2018):

Intel 486DX

    One of Intel's Intel 486 family of
   microprocessors (one of the last before the Pentium).  The
   486DX has a working built-in floating point unit (FPU).  The
   Intel 486SX is effectively a DX with the FPU disabled.  The
   DX has a pin to select the external data bus width (16 or
   32).

   The Intel 487SX is a 486DX with a 486SX pinout.

   (1995-05-09)