On Dec 21, 15:46, Patrick Finnegan wrote:
> On Sunday 21 December 2003 15:03, Fred Cisin wrote:
> > On Sun, 21 Dec 2003, [iso-8859-1] Silvio Finotti wrote:
> > > Thank you all for the replys....
> > > Just discovered a software that claims to read Apple
> > > II disks (and other formats too) using a normal PC
> > Reads Apple ][ disks without no extra hardware?
> > Does it also turn water into wine?
> I too am skeptical, but it has some more information here:
>
> http://www.oldskool.org/disk2fdi/trial.html
>
> along with some more documentation in the ZIP file you can download.
> I'd have to see it to believe it, but who knows...
> One thing to note is that he says it requires a *2nd* floppy drive
for
> non-PC compatible formats. So, I'm guessing he screws with the
floppy
> select lines somehow to "mix" the data streams from two drives and
try
> to get the PC controller to parse it. Still, I'm skeptable that it's
> possible to work well, and I'm fairly certain it can't be reliable.
Having now read the docs, I'm partway to believing it. For those
who've not downloaded the trial copy and read the docs, the trick is to
have the disk to be read in one drive, and a standard disk in another.
Start both drives, start reading the standard disk, but using the
"Read Track" (diagnostic) command, watch for the DMA to start working
(which means it's read a header and has started to transfer the data
stream), and then switch drives and double the data rate setting. The
idea is that by doing this, the FDC sees a valid header and starts
transferring bits, then by doubling the data rate you get the raw data
+ clocks off the other disk.
Then it's a matter of decoding what you have in your buffer; finding
the sync patterns, working out the density and sector sizes, numbers
and so on. I know that can be done, because I've a program (written
about ten years ago) that does it. It uses a 1770 to read raw data
(only from FM/MFM disks though) and then decodes it; it's designed to
copy protected disks and I've never once known it fail, though it
sometimes takes a while to work out exactly what it has in the buffer
and how to write it back. Of course the patterns on Apple and
Commodore disk aren't the same, but in principle it should be doable.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Sun Dec 21 2003 - 16:42:25 GMT