Re: How many...models/types: APPLE ][ computers?

[mjmahon@aol.com (MJMahon)]

In reply to David Empson's question about whether the 5.25" drive required
"tuning" to work with 16-sector formatting..

Nope, the standard drive tolerances (for the SA390, originally) were OK
for
16-sector operation.  The read electronics could always handle the
"nibbles"
that are required for 6/2 coding, and the drive speed tolerances were
tight
enough to work with the new state machine ROM.  So all that was needed
was the state ROM and boot ROM update to enable 16-sector operation.

The 16-sector state machine can also handle the 5/3 nibbles of 13-sector
disks,
and so they can be read directly.  But the new boot ROM was incompatible
with the old 13-sector boot sector code, so equivalent boot code must be 
provided (by BOOT13 or BASICS) to boot a 13-sector disk.

-michael