Re: Reading apple disks on PC

[mjmahon@aol.com (Michael J. Mahon)]

Paul Schlyter replied:

>In article <20030723040500.21622.00000401@mb-m07.aol.com>,
>Michael J. Mahon <mjmahon@aol.com> wrote:
>> Paul Schlyter wrote:
>> 
>>>In article <FTaRa.1576$KZ.854103@news1.news.adelphia.net>,
>>>Steven N. Hirsch <shirsch@adelphia.net> wrote:
>>> 
>>>> sean wrote:
>>>> 
>>>>> Paul Schlyter wrote:
>>>>> 
>>>>>> PC floppy drives have
>>>>>> never been able to read GCR disks and will never be.
>>>>> 
>>>>> 
>>>>> Unless of course you are lucky enough to get your hands on an old 
>>>>> Central Point Copy II option board.
>>>> 
>>>> Hmm.  I have one of these.  However, I'm not aware that the support 
>>>> software lets you read files from, e.g. a IIgs 3.5" disk.  Wasn't it 
>>>> just intended for full-disk copying?
>>> 
>>>I think he meant the capability of the hardware and not necessarily
>>>the accompanying software.  You can always write your own software,
>>>but it's much harder to build your own hardware.... :-)
>> 
>> Considering that it would be necessary to write RWTS
> 
>Only if the hardware is as stupid as the standard Apple II disk
>"controller" (which was only a rudimentary disk controller really;
>the Apple II RWTS was the actual "disk controller").  With any real
>disk controller chip, you just set some parameters in the disk
>controller, then give it a memory address and tell it to read one or
>several consecutive sectors into a buffer starting at that address.

The Copy II Plus Option Board is _not_ a disk controller chip.
It is an extremely low-level device--which is why it can 
capture virtually any bit stream from a disk.

>> and a pretty complete file system (or two) in x86 code,
> 
>Anyone wanting to attempt that are free to borrow as much C code
>as they want from my FID.C (available at
>http://home.tiscali.se/pausch/apple2/)
>to access an Apple DOS file system.

It is good to know that there is source available which could
form the starting point for several file systems.

>> I think this may be yet another case where the hardware is the
>> easyware and the software is the hardware.  ;-)
> 
>Only if the software really would require a complex RWTS equivalent
>and the hardware contained only standard components which you could
>buy fairly easily.  But when I said "build your own hardware" I was
>more thinking of constructing and mask programming your own LSI
>chips....... it's not impossible, but it's definitely not for the
>faint hearted to do such a thing.
> 
>But before speculating more, we need to know more about the hardware:
>does it contain a real disk controller in hardware, which is at least
>reasonably "intelligent"?  Or does it contain only a rudimentary disk
>controller in hardware, like the Apple II did?

The Copy II Plus Option Board is a totally rudimentary bit stream
capture device.  To my knowledge there are _no_ disk controller
chips that have ever supported Apple GCR.  (Even the SWIM chip
is a nibble capture device, comparable to the Disk ][ controller.)

It is also unfortunate that the bit-level I/O available on even the
fastest PCs, like the parallel port, is limited to about 500KHz
sampling rates (due to the legacy ISA timing), and so is not
fast enough to accurately sample head data without interposing
a serial-to-parallel converter running at 2MHz or so.  And then
there are the ubiqitous interrupts of most PC environments...

I've been tempted to build such an adapter to a Disk ][, but so
far there are simpler options for moving data between my //e
and my PC (some involving a Mac  ;-).

-michael

Check out amazing quality 8-bit Apple sound on my
Home page:  http://members.aol.com/MJMahon/