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

Slot A

    The physical and electrical specification for the
   edge-connector used by AMD's Athlon processor.

   The connector allows for a higher bus rate than Socket 7
   or Super 7.  Slot A motherboards use Compaq's EV6 bus
   protocol.  Slot A is mechanically compatible but electrically
   incompatible with Intel's Slot 1.

   (1999-08-05)