Robert Rolf wrote:

> A 1.44 Meg floppy has to double step each track to span the wider
> 720K track.  A 720 has 40 tracks, a 1.44 80.

  Ummm, nope.  Wrong on that one.  A 720K drive is 80 tracks.

> The embedded controller (Korg keyboard) doesn't know how to do that.

  Well, I daresay it doesn't, but that's not the point.

  There was a compatibility problem between 360K 5" floppies and 1.2M 5"
ones.  360K are indeed 40 tracks and the 1.2M are indeed 80 tracks, so a
1.2M did have to double step to read a 360K disk and couldn't write one
(properly, in case we have a dispute on this).

  Now, why did these disks not do 1.44M?  Well, in the 1.2M mode, they
doubled the data rate (simple to do) but also sped up the motor so that
the data was written at less than double the ("double") density.
Altogether rather bizarre.

  Now both 720K and 1.2M drives use 80 tracks, and the motor speed is
fixed.  What happens is that in 1.2M mode, the data rate is doubled
*and* the write current is doubled as well, also the receive amplifier
compensation is changed.  Same speed, double rate, density is doubled.

  And a 1.2M drive can write 720K disks perfectly.  In fact, all up, I
think an ordinary 1.44M drive would operate in the Korg perfectly but it
*may* be necessary to jumper the "density" control line to suit.  I've
never quite found a reference to this control line but it *should* be
out there somewhere.

  Corollary - BIOS detects drive types by stepping the head all the way
inward, 85 or so times then seeing how many steps back it takes to reach
track zero.  It can try different motor speed commands and see if the
index pulses match (depending on the presence of a disk in 5" drives),
but I'm not sure it can determine between a 720K and a 1.44M drive.
--
  Cheers,
        Paul B.