>On Thu, 8 Apr 1999 CLASSICCMP_at_trailing-edge.com wrote:
>>I suspect when you say "MFM" you mean "all the soft-sectored data storage
>>schemes descended from the original IBM 3740 (FM) standard", in which case
>>you're right.
>So, does that mean that those quarter-track schemes used for copy
>protection on the Apple II could also be implemented on a PC or
>Macintosh disk? The reason why I ask is because I've never heard of such a
>practice.
I think my statement is entirely unrelated to your question. The
Apple ][ DOS 3.2/3.3 sector format, while it follows conceptually
the same ideas as the IBM 3740 standard in that they are both ways
of recording blocks of data on floppy disks and both encode the track and
sector number in the header, is not by any stretch compatible with it.
On an Apple Disk ][, you have complete control over the stepper phases,
so quarter- and half-tracking is possible. (You can also blow out
the Apple's power supply by switching the phases on and off at a
certain "bad" rate, too!)
The 34-pin Shugart SA400-style interface used for floppies in PC's
doesn't allow half- or quarter-track stepping, though you could
imagine trying to read or write something while rapidly stepping in/stepping
out. If you want more information, I highly recommend that you read
the Shugart SA400 interface documents, or the interface documents of
a drive with a similar interface (i.e. the TEAC datasheets, which are
also very complete.)
I don't know of any documentation of the Macintosh 3.5" floppy interface.
If someone could point me towards the relevant documents (or even the
part numbers they claim to describe) I'd be quite happy!
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Fri Apr 09 1999 - 15:18:31 BST