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

Athlon
AMD K7
K7

    (K7) AMD's 7th generation x86 processor,
   released in June 1999.

   Athlon uses a Slot A motherboard and is not compatible
   with Slot 1 motherboards.

   [Details?  Reference?]

   (1999-08-05)