Re: Apple 3.5" drive questions

[russotto@grace.speakeasy.net (Matthew Russotto)]

In article <b411bl0470@enews4.newsguy.com>,
Charlie <charlied@NOSPAMbboard.com> wrote:
>Recently, through the work of Simon Williams, a problem long held to be a
>hardware incompatibility was solved by software.
>This made me wonder for the millionth time if software could solve the problem
>of reading and writing MS-DOS with an 800k Apple 3.5" floppy drive connected to
>an Apple II.
>
>Yes, I know, this is supposed to be impossible.  The hardware is supposed to be
>incompatible with writing MS-DOS.
>
>What I don't know is why.

Because the PC controller does MFM in hardware, and the Apple format is
NRZi/GCR (D5 AA 96....DE AA, just like the 16-sector 5.25 format).

>One guess would be that the Apple firmware doesn't allow for maintaining the
>same disk rotational speed.  MS-DOS disks rotate at the same speed no matter
>which track the head is on.  Apple disks vary the speed.

That could be a factor too, though I believe later drives kept a
constant speed and varied the bit frequency.



-- 
Matthew T. Russotto                            mrussotto@speakeasy.net
"Extremism in defense of liberty is no vice, and moderation in pursuit
of justice is no virtue."  But extreme restriction of liberty in pursuit of 
a modicum of security is a very expensive vice.