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

Fairchild F8

    An 8-bit microprocessor.  The processor itself
   had no address bus - program and data memory access were
   contained in separate units, which reduced the number of pins
   and the associated cost.  It also featured 64 registers,
   accessed by the ISAR register in cells (register windows) of
   eight, which meant external RAM wasn't always needed for
   small applications.  In addition, the 2-chip processor didn't
   need support chips, unlike others which needed seven or more.

   The F8 inspired other similar CPUs, such as the Intel
   8048.  The use of the ISAR register allowed a subroutine to
   be entered without saving a bunch of registers, speeding
   execution - the ISAR would just be changed.  Special purpose
   registers were stored in the second cell (regs 9-15), and the
   first eight registers were accessed directly.  The windowing
   concept was useful, but only the register pointed to by the
   ISAR could be accessed - to access other registers the ISAR
   was incremented or decremented through the window.

   (1994-11-16)