Copying Mac Disks with a Single Drive

Fred Cisin cisin at
Thu Feb 8 23:46:12 CST 2007

> >> with an external 400 or 800k floppy. The SuperDrive (original
> >> SuperDrive, not the "new" CD/DVD one) [present on all Macs since the
> >> IIx, many IIs and some SEs (SE FDHD)] has the smaller head size and
> >> your older machine won't read it properly. WRT the swapping- can't
> >
> > There is a completely different recording method (MFM v Mac GCR).
> >
> > What are the dimensions of the different size heads?

On Thu, 8 Feb 2007, Scott Quinn wrote:
> Not sure about dimensions- the 800/400k drives I think share common
> dimensions with the PC-esque 720k drives, and the 1.4 SuperDrive is
> known to be the same dimension as the 1.44 MB PC mechanism.

PC 720K and 1.4M drives have the same size head.

> It was  big issue around the time System 7 came out- if you put a 800k
> diskette in a System 7 machine with a SuperDrive the desktop file would
> be rewritten unless the disk was locked. If you then put the disk in a
> 800k System 6 drive it would indicate it as corrupt (you could run it
> through Disk First Aid to get it back) because of the head sizes
> (similar to the problem with 5.25" DD floppies in the PC AT)

THAT was an issue with a different width and number of cylinders/tracks
per side.
(40 cylinders/tracks per side at 48tpi V 80 cylinders/tracks per side at
96 tpi)

PC 720K, Mac 400k/800k, PC 1.4M, Mac 1.4M disks all have 80 cylinders/80
tracks per side. all at 135 tpi.

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