From: firstname.lastname@example.org (Mark Zenier)
Subject: Re: Looking for MFM endec description
Date: Tue, 8 Oct 2002 18:33:30 GMT
Organization: Eskimo North www.eskimo.com (800) 246-6874
NNTP-Posting-Date: 9 Oct 2002 17:24:07 GMT
In article ,
>I can't seem to find a definitive description of an MFM
>I'm looking at the bits on the edge connector of a drive, and I'm just
>not "getting it".
>Any pointers would be greatly appreciated. All the google references
>I've found so far are either too general (vague) or descriptions of
>the outside of some chip or IP.
I assume you're looking at a floppy disks. This info dates back to the
era before "everything is on the internet".
The holy grail(s), that I've never seen, are a couple of IBM documents
that describe the original systems. GA21-9182-0, GA21-9176-0, GA21-9190-1
are the old document numbers from 20-25 years ago. Also there's a
Shugart Assoc. "Double Density Design Guide" that's refered to in some
of the stuff I've found.
For current stuff, the floppy disk formats have ISO standards. The usual
1.44 megabyte 3.5 inch diskette is covered in ISO (IEC?) 9529/1 for the
media and (for the stuff you're interested in) ISO 9529/2 which describes
the format, encoding, and CRC algorithm. ISO 8630 (3 volumes) covers
1.2 meg 5 1/4 inch disks. ISO 7487, the 360k byte 5 1/4 inch disks.
These are kind of distilled down. If you can find a datasheet for
one of the floppy disk controller chips, there's a bit of stuff
the standards gloss over, like the sector length encoding. The
National PC8477 has a nice fat datasheet if you can still find it
online. Try National's obselete section. Or SMSC (formerly SMC, aka
Standard Microsystems or something like that for) for their multi-io
Here's some other stuff that I found, last winter, doing a literature search
with the idea of an open source floppy controller.
Encoding/Decoding Techniques Double Floppy Disc Capacity
Computer Design, February 1980
Double density floppy disk controllers
Mini-Micro Systems, November 1978
FD179X Application Notes
Western Digitial Corporation, June 1980
(Also the 179X and 279X floppy disk controller datasheets)
Mark Zenier email@example.com Washington State resident