need 720k 3 1/2" disks

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Jun 10 19:13:50 2003

> EVERY DSHD drive can read "DSDD" diskettes, so long as the disk controller
> supports the lower (250K) data transfer rate, and the correct
> software is present. That includes every disk controller that you have
> ever seen, although Tony and a few others may have some that were
> originally designed for 8" that do not support the lower rates.

A _really_ obscure example, relating to 3.5" disks...

The original 3.5" drives rotated at 600rpm, and therefore transfered data
twice as fast as the corresponding PC drives, which rotate at 300 rpm.
Now by an amazing coincidence, this data rate is the same as the HD data
rate for a PC drive.

So a controller for the original 3.5" drive should be able to handle a PC
HD drive (same data rate) with the correct programming (it would be able
to fit more sectors on a track than it could with the double-speed DD
drive, and would have to not moan because of the longer wait for an index
pulse). But this controller couldn't handle a DD disk in a normal PC drive...


-tony
Received on Tue Jun 10 2003 - 19:13:50 BST