Re: Trackstar can use IBM 360K floppy drives to R/W Apple disks?

["Redskull" <redskulldc@yahoo.com.au>]

"Frank Townsend" <ftownsen@iamdigex.net> wrote in message
news:Fmkz9.12093$Dl.7443@nwrddc01.gnilink.net...
> Looking at the Trackstar E manual, I read the following:
>
> "The Trackstar Disk Adapter Cable connects your Trackstar E to the 360k
> MS-DOS disk drive(s).  Its presence allows the 360k drives to read and
write
> Apple floppy diskettes.  This will in no way interfere with the operation
of
> the 360k dives(s) under MS-DOS."
>
> "Note: 1.2 Mb 5.25" disk drives cannot read Apple diskettes- even if they
> are capable of reading MS-DOS 360k software."
>
>
> Could some wise person explain this to me?  I thought, obviously
> incorrectly, that  MFM drives could not decode GCR encoded diskettes?  But
> is this untrue for 360k drives?  I'm confused.

That is not exactly true.

By default, 1.2Mb 5.25 floppy drives run at a different RPM, and a different
bit-transfer rate than 360k 5.25 drives.
1.2Mb drives can also operate as 720k mode. In this mode they are using
the same rotational speed and transfer rate as 360k floppies.
Most 1.2Mb drives can be permanently jumpered for 80Tk DD operation.

The problem then becomes the width of the read/write element in the head of
the drive,
and the track density of the drive which is up to 96TPI (tracks per inch)
instead
of the 48TPI of the 360k models.

The 96TPI is not a problem, since you can just double-step the head between
tracks to obtain 48TPI.

The width of the R/W head IS a problem. Imagine the following scenario:

1) A disk is formatted, and written to with a 360k drive. No Problem.

2) The disk is then read by a 1.2Mb drive in DD(720k)mode. The thinner R/W
element on the 1.2Mb drive reads the track data that was written by the 360k
drive with no problem.

3) The disk is then written to by the 1.2Mb drive in 720k mode. The thinner
R/W
heads writes data back to the disk in a thinner path, which does not
completely
cover the width of the 360k track data. As long as the diskette is left in
the 1.2Mb
drive there is no problem, since the drive is only reading and writing it's
own
thinner track data.

4) The diskette is put back in a 360k drive. The wider read/write head reads
both
the thinner track data produced by the 1.2Mb drive, and also the remnants of
the wider track data that it originally produced. The results can produce
anything from
random errors, to complete read failure in the 360k drive. Put the diskette
back
in the 1.2Mb drive and it will function correctly, since only the thinner
track data
is being used. Only solution is to re-format the disk on a normal Apple
drive, to
ensure that each track is wide again.


Rule: Don't write to a Apple floppy with a 1.2Mb drive if you ever plan to
use it
in a standard Disk][ drive afterwards.

Other things to watch out for:

DON'T EVER use HD 5.25 floppies in Apple drives, or in 1.2Mb drives while
in 80Tk DD mode.
They may appear to work initially, but they will fail quickly over time. HD
floppies
are written with a higher level of current passing through the read/write
head in
HD mode, due to the fact that the magnetic material on the disks is slightly
different
composition. Writing to HD floppies with DD level currents, will not produce
the
required magnetic arrangement of particles on the diskette. It may work for
a while,
but it WILL fail after a relatively short period of time.
Typical syptoms are trying to read a diskette a month or two later, and
finding it
has random garbage across the entire surface.


Hope this helps,

Red