8" floppy project

From: Don Hills <dmhills_at_attglobal.net>
Date: Thu Jul 29 04:28:42 2004

Some points which may be of assistance:

A long time ago, I built and maintained a PC-AT based system for
reading/writing 8 inch diskettes. It used a 3rd party floppy controller card
that supported FM mode(*), and an 8 inch drive from an AS/400. The
crucial thing about the drive was that it was electrically "5.25 inch"
compatible - it used the PC interface card-edge data cable and PC 12V/5V
connector. In fact, it looked like an enlarged half-height 5.25 inch drive
from the front, complete with beige finish and turn-type locking handle.

Several DOS disc copy programs of the era supported FM mode for 5.25 inch
diskettes on a track-by-track basis, which therefore also worked for the 8
inch drive on 3740-format diskettes (index track FM, the rest MFM). I mainly
used an IBM Internal program to handle reading/writing images in IBM's MIF
format (an standard file format for storage and transmission of all forms of
machine binary data, from punch cards to EPROM images to diskettes to
tapes.)

I gather from reading the archived thread that your requirements are
somewhat more exacting, in that the density changes within a track (FM
header and MFM data for each sector). Am I correct, or is it in fact just
3740 style (Track 0 FM, 1-73 MFM)? I have written code to operate the NEC
765 controller directly to handle unusual formats, but I've never tried
mixed densities on one track.

(*)The standard AT controller supported FM mode, too. I won't go into the
history of PC controllers that did or did not support FM mode here, but the
facts will be familiar to anyone who uses a PC to read/write 5.25 inch
diskettes for BBC micros.

-- 
Don Hills    (dmhills at attglobaldotnet)     Wellington, New Zealand
It's ironic that people who are too smart to engage in politics
are governed by people who are not as smart.
Received on Thu Jul 29 2004 - 04:28:42 BST

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