On 11/03/2013 10:14 AM, Dave wrote:
  Floppy is about 0.5Mhz Hard Disk is 10MHz 
ST506-type hard disk?  My manuals way 5MHz; RLL 7.5Mhz.  Perhaps ESDI,
but that's a different kettle of fish.
Point being that it's possible to emulate a HD 500Khz floppy using an
8MHz AVR; an 80MHz ARM is quite tame.
--Chuck