Or on the Epson RC20! 
 The Epson TF20 (floppy
drive for the HX20, PX4, PX8, etc) contains a Z80
 and 64K RAM. Oh, and a boot ROM that is mapped out after booting. I have
 never analyhsed the system disk in detail, but I have a feeling this
 thing runs CP/M internally.
 
  The PX-8  is a CP/M system based on Rom and Ram disk with
 hooks for external extension for both greater rom/ram disk or
 the floppy device. 
 
Sure, as is the PX4 (I have both). The HX20, of course is not (it uses a
pair of 6303 microprocessors). But the 5.25" floppy drive appears to run
CP/M (or something close) on its intenral processor. The 3.5 drive, BTW,
doesn't...
-tony