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

primary cache
L1 cache
level 1 cache
level one cache

    (L1 cache, level one cache) A small,
   fast cache memory inside or close to the CPU chip.

   For example, an Intel 80486 has an eight-kilobyte on-chip
   cache, and most Pentiums have a 16-KB on-chip level one
   cache that consists of an 8-KB instruction cache and an 8-KB
   data cache.

   The larger, slower secondary cache is normally connected to
   the CPU via its external bus.

   (1997-06-25)