[HP9895 format deleted] > I wonder if this is the same format the Amigo used?
Which was the Amigo? FWIW every 5.25" and 3.5" HP drive unit that I've seen (and the internal drives on the 9826 and 9836) use a Western Digital or compatible disk controller chip. The low-level format (sync bytes, headers, etc) are what you'd expect for such an IC. -tony
