Universal drive

From: Allison J Parent <allisonp_at_world.std.com>
Date: Thu Oct 1 22:31:17 1998

< > this for all conventional formats, but not Apple disks. It would be
< > nice to connect one of these and read the disk image into a file.
< > The main reason why I ask is for rescuing messed up floppies...

Apple used GCR coding for their drives and there are no commonly
available chips that do. In fact the apple does not use the traditional
floppy disk controller chips at all. The FDC logic on the Apple is
rather simple and the CPU provides the brains as a software FDC.
It was part of the idea of using software to replace hardware to make
the machine simpler and less expensive.

< PCs use a disk controller chip based on an NEC 765 design that can not
< read ANYTHING other than MFM (some can also do FM), with IBM 3740 style

Excuse me! That is patently incorrect! If you qualified that as *most
PC controllers cannot read some formats* that would be true.

The 765 and all of the chips based on the 765 core can read FM encoded
disks. It's not always possible with PC based designs as some are
hardware crippled (sloppy data sep circuits) and most of the PC bios code
is marginally brain dead.

However the 9266, 37c65 and 92c665 have been seen doing FM.

In the mean time my S100 card design and the compupro DISK1A both happly
read 8" SSSD (FM) disks and even single density 5.25 media.

< The Western Digital disk controller chips (179X, before they changed ove
< NEC style) could do a reasonably real track read of anything MFM
< regardless of sector header structure.

Try the 765 read diagnostic command. Hex 02 (fm) or 42 for MFM.

<They were used in TRS-80s and a LOT of machines OTHER THAN PC.

The TRS80 used the 1771 that was FM only.

the WD 177x or WD179x still cannot read an apple disk.

Allison
Received on Thu Oct 01 1998 - 22:31:17 BST