4 Nov
2022
4 Nov
'22
12:15 a.m.
On Thu, 3 Nov 2022, Sellam Abraham via cctalk wrote:
There was a project someone did years ago where you
can read GCR disks in
an unmodified PC drive by first inserting a PC formatted disk to get synced
and then swapping in a GCR encoded disk, then it can actually read the raw
pulses and they get decoded in software. I forget the website where the
project can be found but a web search will hopefully turn it up.
There are some strange tricks that you can do to fool the system and get
it to read some stuff that is NOT IBM/WD sector/track structures.
For example, Amiga is MFM data stream, but without IBM/WD sector/track
structures. You can fool the NEC FDC into seeing it, in several ways, one
of which is to switch drives in mid read, and/or to read a "long" sector.
I never succeeded with any of the tricks for Apple2 GCR.
About 35 years ago, I did the file system code to use with an extra board
("Apple Turnover") to go between the FDC and the drive, for Apple2 disks
(Apple-DOS 3.2 (13 sector), 3.3 (16 sector), Softcard CP/M, P System, and
ProDos) It never worked well, and the publisher got in too far over their
heads, and I had to have a lawyer shut them down.