Re: msdos 3.5" disks with apple 3.5" drives

[David.Empson@bbs.actrix.gen.nz]

In article <1lhr2h$aev@agate.berkeley.edu> chiu@ucsee.Berkeley.EDU (David Chiu) writes:
> 
> If I remember correctly, some owners of PC Transporter complained that at
> times 720k disks formatted by PCT cannot be read on generic IBM clones.

Quite true.  It usually depends on the DOS machine.  I've found that
disks formatted on the PCT can be accessed on the two PC clones I've
tried, but only as far as track 15.  Beyond that, it gets errors.

(Track 16 is the first one at which the Apple 3.5 Drive changes the
revolution speed.)

I think the PC Transporter tries to compensate for the variable
revolution speed of the drive by adjusting the bit cell widths on the
inner tracks.  It can't get the width exactly right.  There isn't
enough accumulated error over one sector to cause problems, but over
an entire track, the real PC can't cope with the bits being out of sync.

Writing to disks that have been formatted on a PC clone is OK, its
just formatting them on the PCT that causes problems.


My solution is to use a SuperDrive (and its controller card) in
conjunction with the PCT.  I tell the PCT to use Slot 6, Drive 1 (the
SuperDrive) as drive A.

I've found that this works reasonably well with 720k and 1.44MB disks,
with a few provisos:

- The PCT software scans the drive at startup to find out how many
blocks it has.  This means that you can't mix 720k and 1.44MB disks
during the session, and have to put a disk of the appropriate type
into the drive before launching AEPC.SYSTEM.  If you want to use the
other size, you have to exit to ProDOS, put the other type of disk in
the drive, and launch AEPC.SYSTEM.
Unless you want to boot from the disk, you have to eject it before the
PCT tries to boot (at the end of the memory test).

- I have been unable to format 720k disks in the SuperDrive.  800k and
1.44MB is OK, but not 720k.  I suspect this is a limitation of the
controller card (it lists 720k in the format options under GS/OS, but
the option is dimmed).

- If you use disks that have been formatted on a real PC, they will
have a 1:1 interleave.  The SuperDrive card is very slow writing to
disks with 1:1 interleave (reading is fine).  I haven't had any
problems with 1.44MB disks formatted by the PCT (at 1:2 interleave) -
a real PC seems not to care about the interleave.


I'll just repeat myself here: I am using the SuperDrive connected to
its own controller card, NOT to the PC Transporter.  The PCT is
treating it as a ProDOS floppy drive, accessing it at block level to
get at the MS-DOS file system.
-- 
David Empson

Internet: David.Empson@bbs.actrix.gen.nz    EMPSON_D@kosmos.wcc.govt.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand