Re: Reading apple disks on PC

[pausch@saaf.se (Paul Schlyter)]

In article <APMQa.2286$r8.407@nwrddc02.gnilink.net>,
Michael Pender <mpender@hotmail.com> wrote:
 
> Charlie <charlied@NOSPAMbboard.com> wrote in message
> bevseq01g3@enews2.newsguy.com">news:bevseq01g3@enews2.newsguy.com...
>
>> It is my understanding that Apple 5.25" drives cannot read/write MFM
>> at all.
> 
> I don't see why not - the Apple 5.25" drive is controlled entirely by
> software.
 
Not quite...
 
The Apple II disk controller card has two ROMs of 256 bytes each.
The first contains the boot code.  But the second isn't available
at all from the 6502 address bus -- it's a "state machine ROM"
used by the hardware logic on the disk controller card.
 
When the Apple II switched from 13-sector to 16-sector disks, both
ROM's had the be upgraded.
 
> With a change to the software it should be able to read MFM disks
> without difficulty.
 
...you'd have to change the "state machine ROM" as well.  It needed
an upgrade when Apple went from 13-sector to 16-sector disks.
 
> Of course, saying that it is *possible* is very different than
> saying its worth the time to do.
 
It's at least impossible without updating the "state machine ROM".
And updating that just to read MFM disks on the Apple II isn't
worth doing....
 
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