30 May
2000
30 May
'00
10:07 a.m.
I always figured the reason for the restriction was
dumb boot PROMs, which
only know how to do programmed I/O to the FDC, and 8" DD comes in too fast
for typical 8-bit CPUs of the time to handle with PIO. If the boot PROM on
a particular system is smart enough to set up DMA, no need to require SD.
it's an artifact of how people though the DDmedia was speced by IBM and
a lack of knowledge of CP/M boot as everyone just followed the book blindly.
Not all required {or even had it!} DMA to do DD, CCS didn't.
I'd add that DMA was mostly uncommon save for the more refined or robust
systems.
Allison