9 Feb
2007
9 Feb
'07
5:46 a.m.
>> 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.