Apple II <-> Commodore 64/128 disks?

[William McBrine]

The Apple II FAQ states that Apple disks are incompatible with IBM PC
drives, and vice versa, because Apple drives use GCR encoding, where PC
drives use MFM. This got my attention, because the Commodore 64's 1541
drive also uses GCR -- and the 128's 1571 drive is a dual mode drive, so
it can exchange data with PC drives. (The MFM mode was originally meant
for use with CP/M, but can work with MSDOS disks, too.)

Is there any software for the Apple II OR C64/C128 to enable one system to
read and/or write the others' disks?

--
William McBrine | http://www.clark.net/pub/wmcbrine/html/
wmcb...@clark.net | Unsolicited commercial emailers will be annihilated

[Tony Cianfaglione]

There used to be an addon for the C64 called Trackstar 128 which
allowed you to run Apple II software.

----------------------------------------------------

[David Empson]

William McBrine <wmcb...@clark.net> wrote:

> The Apple II FAQ states that Apple disks are incompatible with IBM PC
> drives, and vice versa, because Apple drives use GCR encoding, where PC
> drives use MFM. This got my attention, because the Commodore 64's 1541
> drive also uses GCR -- and the 128's 1571 drive is a dual mode drive, so
> it can exchange data with PC drives. (The MFM mode was originally meant
> for use with CP/M, but can work with MSDOS disks, too.)
>
> Is there any software for the Apple II OR C64/C128 to enable one system to
> read and/or write the others' disks?

GCR is a general technique, not a specific encoding method (unlike MFM,
which defines the bit-level and sector-level encoding).

The key point with GCR is that a table lookup is used to map between
data bytes and valid "disk bytes", in conjunction with some method of
splitting up the data bytes.

For example, on 5.25" disks, Apple has used three different techniques,
all which can be called "GCR".

The addressing information is encoded using "4-and-4" (two disk bytes
per data byte), since this is easy to decode quickly (shift and AND).
This is effectively how "FM" encoding works - a clock bit is written
before each data bit, so half the bits on the disk are available for
data (ignoring sector overheads).

DOS 3.2.1 and earlier (13-sector) used "5-and-3", where each data byte
was split into 5-bit and 3-bit fields, and there are 32 possible disk
byte values. Eight disk bytes are written for every five data bytes.
This allows the disk to hold 25% more data than 4-and-4.

DOS 3.3, Apple II Pascal, ProDOS and CP/M (also Apple III SOS, and
Macintosh/Apple II 400K/800K 3.5" disks) use "6-and-2" encoding, where
each data byte is split into 6-bit and 2-bit fields, 64 disk byte values
are available, and four disk bytes are written for every three data
bytes. This allows the disk to hold 20% more data than 5-and-3, or 50%
more than 4-and-4.

On top of this is the specification of what mapping is required between
disk and data bytes, where the leftover bits are stored, and the general
track organisation into sectors.

There is also the issue of the design of the disk controllers. One
feature of the Apple II disk controller is that every disk byte must
have bit 7 set, which may not be true for other computers.

In summary: provided the C64 and Apple II use fundamentally compatible
disk drives and recording speed (the Apple II is single density, 35
tracks, single sided, 4 microseconds per bit cell) and there are no
encoding methods used on either machine which are unreadable by the
other machine's controller (e.g. the Commodore also requires bit 7 set
in each disk byte), then it should be possible to read the disks in
software.

I'm not aware of any software that does this.

--
David Empson
dem...@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand

[Nathan Mates]

In article <5rtsap$p...@clarknet.clark.net>,

William McBrine <wmcb...@clark.net> wrote:
>The Apple II FAQ states that Apple disks are incompatible with IBM PC
>drives, and vice versa, because Apple drives use GCR encoding, where PC
>drives use MFM. This got my attention, because the Commodore 64's 1541
>drive also uses GCR -- and the 128's 1571 drive is a dual mode drive, so
>it can exchange data with PC drives. (The MFM mode was originally meant
>for use with CP/M, but can work with MSDOS disks, too.)

The Commie drives have a microprocessor builtin, making them
capable of reading both MFM and a form of GCR. The Apple II 5.25"
drives are considerably 'dumber', requiring the host computer to take
care of most of the timing requirements, decoding, etc. Basically,
without rare addon hardware, the Apple II can't read other platforms'
disks. The C64 might be able to do more simply by starting with
better specs.

Nathan Mates
--
<*> Nathan Mates http://www.visi.com/~nathan/ <*>
# What are the facts? Again and again and again-- what are the _facts_?
# Shun wishful thinking, avoid opinion, care not what the neighbors
# think-- what are the facts, and to how many decimal places? -R.A. Heinlein

[Joe Kohn]

William McBrine <wmcb...@clark.net> wrote:
>the Apple II FAQ states that apple disks are incompatible

>with IBM PC drives, and vice versa

Oh?

At KansasFest, with the whole world watching, I popped a blank 3.5"
HD disk into a SuperDrive attached to a IIGS, and while still in the
Finder, formatted it for MS-DOS. I then copied some files from my
Focus hard drive to the MS-DOS formatted disk...all without ever
leaving the Finder.

Unfortunately (or, fortunately - depending on your perspective) no
one at Kfest had a Wintel machine, but had there been one there, I
would have then popped the disk into the Wintel machine, and it would
have been recognized as an MS-DOS formatted disk.

Any Apple IIGS owner might be able to perform that same magic trick
this week or next; it all depends on what the beta test team says.

Stay tuned for details...

Joe Kohn
http://www.crl.com/~joko

[MJMahon]

Joko wrote:

>At KansasFest, with the whole world watching, I popped a blank 3.5"

>HD disk into a SuperDrive attached to a IIGS...

Ah, but we were discussing 5.25" disks.

-michael

Email: mjm...@aol.com
Home page: http://members.aol.com/MJMahon/

[Mitchell Spector]

In article Joe Kohn <jo...@crl.com> writes...

>William McBrine <wmcb...@clark.net> wrote:
> >the Apple II FAQ states that apple disks are incompatible
> >with IBM PC drives, and vice versa
>
>Oh?
>

>At KansasFest, with the whole world watching, I popped a blank 3.5"

>HD disk into a SuperDrive attached to a IIGS, and while still in the
>Finder, formatted it for MS-DOS. I then copied some files from my
>Focus hard drive to the MS-DOS formatted disk...all without ever
>leaving the Finder.

Ahh, sounds like Peter finally completed MUG NDA. This is certainly
good news, especially since the introduction of Windows 95 seems to (at
least in my experience) rendered the MSDOS.FST unusable. Whenver you
write to a disk from Win95, the Finder refuses to see that disk again.
MSDU is able to read and write just fine, but it never was a quick and
easy task, in fact I found it faster to just format a high-density
ProDOS diskette and bring it over to the IBM side to read.

From the sounds of things, MUG is the next best thing to a fully
functional MSDOS.FST (which will probably never happen anyway). :)

Mitchell Spector
sp...@vax2.concordia.ca

[Johnny Lau]

Tony Cianfaglione (ab...@chebucto.ns.ca) wrote:
: There used to be an addon for the C64 called Trackstar 128 which

: allowed you to run Apple II software.

But wasn't the Trackstar an addon for XT's?

Anyway, I was recently given a Spartan which according to the manual is a
computer onto itself which emulates an Apple II+ by plugging into the
back of a Commodore 64.

--
- This is not Johnny Lau of lemonworks at be...@freenet.toronto.on.ca.
- Rene Magritte's "The Treachery of Images".

[Tony Cianfaglione]

I have an old K-Power issue that has an ad for the Trackstar 128 as
well as a Spartan in another part of the magazine. They look like
competing devices. I wasn't aware of the XT Trackstar. Possibly, they
made versions for various computers.

------------------------------------------

[Jeff Blakeney]

On Mon, 11 Aug 1997 13:24:31 GMT, be...@torfree.net (Johnny Lau)
wrote:

>Anyway, I was recently given a Spartan which according to the manual is a
>computer onto itself which emulates an Apple II+ by plugging into the
>back of a Commodore 64.

Yes, that is what it is. If you plug a II+ keyboard into the CPU card
with a Disk ][ card in slot six, you can use it as a stand alone 64K
II+ computer. Actually, I think that the II+ part is completely
contained on the CPU card and I've toyed with the idea of making a
portable II+ with it but have pretty much put it aside as it would be
of limited use to me.

With a Commodore 64 plugged into the front on the Spartan, the 64 will
then act as a smart keyboard. You can use the C= (Commodore button)
with the other keyboard keys to send entire keywords to the II+. I
can't remember them exactly anymore thing like C= P would be the same
as typing PRINT, C= L would be the same as typing LIST, et al.

By the way, would it be at all possible for me to get a copy of the
Spartan manual. I have a Spartan and an extra CPU card but I never
got a manual with mine. E-mailing a text version would be wonderful
but I might be able to send you a couple bucks to mail a photocopied
version.