"Michael J. Mahon"  wrote in message 
news:DsmdnTGdt9BUfxTUnZ2dnUVZ_qninZ2d{at}giganews.com...
> Charlie wrote:
>> "Steven Hirsch"  wrote in message 
>> news:1p6dnXqfLPZZdhXUnZ2dnUVZ_jOdnZ2d{at}giganews.com...
>>> Charlie wrote:
>>>> "Steven Hirsch"  wrote
in message 
>>>> news:YdKdnWEBU6Dx5RXUnZ2dnUVZ_h2WnZ2d{at}giganews.com...
>>>>> Alex Freed wrote:
>>>>>> sicklittlemonkey wrote:
>>>>>>> Are you talking about reading actual Apple II
disks, a la FDI etc, 
>>>>>>> or
>>>>>>> just reading and writing to modern HD media
via an emulation of 5.25 
>>>>>>> &
>>>>>>> 3.5 GCR formats?
>>>>>> After posting I remembered that the Apple
3.5" disks were "special".
>>>>>> AFAIK they use variable speed to using a PC drive
to read/write Apple
>>>>>> 3.5" disks is at least difficult.
>>>>> Wouldn't it be possible to cleverly emulate the
variable speed zones 
>>>>> in software by playing with the data rate?  (For some value of 
>>>>> cleverness at any rate).
>>>>>
>>>>> Steve
>>>> Yes, Disk2FDI manages to read Apple 3.5" disks in PC
type (single 
>>>> speed) 3.5" drives.
>>> I didn't realize that disk2fdi worked with 3.5" drives!
>>
>> It also supports 3" drives (whatever they are) and 8"
drives.  I've found 
>> when reading 3.5" Apple II disks there is an occasional disk
that won't 
>> read in either the upper tracks or the lower tracks.  Using a different 
>> 3.5" PC drive usually cures the problem.
>>
>>> Another example is the Copy II Plus option board.  Unless I'm confusing 
>>> it with something else, it was able to read and duplicate 800K Mac 
>>> diskettes (same low-level format, I think).
>>
>> I'm not familiar with the Copy II Plus board but another interesting card 
>> is the PC Transporter.  It can read/write an Apple II 3.5" drive in 
>> either GCR with the variable speed (800K) or PC MFM with single speed 
>> (720K).  In this case though, I don't believe the speed is done in 
>> software.  If I remember correctly the PC Transporter somehow keeps the 
>> speed from varying in the drive.
>
> PC drives are not even capable of the "zone" speed changes that Apple
> 3.5" drives do.  To read or write an Apple GCR 3.5" disk
with a PC drive
> requires changing the bit clock rate.

Yes, I understand that Disk2FDI does this (for reading anyway).

What I was trying to say was that the PC Transporter does the reverse.  It 
reads and writes to 800K 3.5" Apple drives using a single speed when doing 
MFM 720K so that the disks can be used in a PC.  I've never seen any 
documentation on how that is done.  I originally assumed (before owning a 
PCT) that an Apple drive automatically adjusted its rotational speed when 
the head moved to different track zones, but I'm pretty sure that when I 
formatted a MS-DOS disk I couldn't hear the speed changing (I don't have my 
PC Transporter set up in my Apple II any more so I can't double check 
myself).

So:

PC drive = single speed for all tracks.
Apple 3.5" drive = multiple speeds in zones *or* single speed for all 
tracks.

I probably shouldn't have brought up the PC Transporter in this thread 
because it confuses the issue.  Its just that nothing I've ever read from 
Apple gives any indication that the rotational speed of the drive can be 
controlled from outside the drive.

Charlie
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