Re: GCR*MFM=FM

["Bill Garber" <willy46pa@comcast.net>]

Michael J. Mahon <mjmahon@aol.com> wrote in message
20030309054309.10901.00001695@mb-dh.aol.com">news:20030309054309.10901.00001695@mb-dh.aol.com...
> In article <7c-dnf9g-vXF-fejXTWcrg@comcast.com>, "Joel"
> <joelbuckley54.nospam.@hotmail.com> writes:

> I'm not so sure that current PC drives/controllers can deal with
> SSSD format--maybe someone here knows?

Sorry, but only 360k can read/write single sided disks.
--

Bill @ GarberStreet Enterprises
http://garberstreet.netfirms.com



> >So by limiting yourself to 35 track single-sided FM (4+4), I think you
might
> >be able to have a disk readable and writeable on both Apple and IBM 5.25
> >drives.
> >Just imagine the impact such a program would have had 20 years ago!
> >
> >3.5 drives-I don't know. I was never really familiar with the workings of
> >Apples 3.5 drive. Clearly the IBM can't read Apple's 800k. But could the
> >Apple read a 720k IBM. I don't know. I thought the increase in data
density
> >on Apple's 3.5 drive was due to putting more blocks per track on the
outer
> >blocks, rather than the encoding format. But I seem to remember that the
IWM
> >was used in the 3.5 drive controller as well, so I'm not really sure.
>
> You are correct about where the extra capacity comes from.  But Apple
> 3.5" 800KB disks are still GCR, using essentially the same encoding as
> the 5.25" disks.
>
> In the "parent" of this thread, Eric Smith suggested that it might be
possible
> for an Apple II to read an FM single-density disk by reading each track
two
> or more times, and correlating the bit-shifted results to determine the
> original
> content.  I replied with a proposal that might be able to do it in one
rotation
> per track by sampling the controller's shift register three times per
"nibble".
> I think that the Apple II could do this with 5.25" disks, but 3.5" disks
would
> be too fast for it to work.
>
> There would have to be some heuristics to determine correct nibble sync,
> but it should be possible.  Of course, a SSSD (90KB) disk is not the most
> practical data interchange medium for either a PC or an Apple II.  ;-)
>
> -michael
>
> Check out amazing quality 8-bit Apple sound on my
> Home page:  http://members.aol.com/MJMahon/


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