Reading/writing floppies for C64 and MS-Dos ???

[Skybuck Flying]

http://trixter.wordpress.com/2008/09/28/the-diskette-that-blew-trixters-mind/

Kinda interesting.

This describes marking sectors as bad in an interleaved fashion so it might
work on C64 and MS-Dos... fat 12 floppies ?

Question is... does it actually work ?

Makes me wish I still had a C64 to try it out !

Anyway how much thruth is there in this story...

I think C64 floppies worked by burning something onto it... while PC
floppies work with magnetic stuff ?

Or am I mistaken in that part ?

Or is this just a software only trick ? Hmm...

Bye,
Skybuck.

 

[Skybuck Flying]

I am not sure what kind of technology these C64 1541 drives used but here is
something interesting in this article:

http://en.wikipedia.org/wiki/Commodore_1541

It mentions how the upper tracks were not used because they were less
reliable !

I think the same can be said for some... if not all CD-Media... where the
upper tracks seem to be of much less quality !

Be it media quality or burning quality !

Wow this could actually mean the C64 Disks were more reliable than todays
cd/dvd crap ! LOL.

Will we all be using C64 disks in the future ! LOL

Bye,
Skybuck.

 

[Skybuck Flying]

The C64 FDC simply used a different format using DIFFERENT HARDWARE
which made them incomptible.

What's the difference then ?

Yes, the Commodore had a drive that could read and write both formats,
because BOTH FDCs were incorporated, and the hardware was flexible
sufficently to write both formats.

Hmm like a dvd/cd drive which can read both formats

NO BURNING, idiot!

Well there must be some truth to it ?!?

Maybe it had something to do with the heads touching/rubbing over the
floppies

I can remember those floppies could get quite warm... could be because the
floppy drives themselfes were warm ?

Those floppies didnt seem to magnetic to me

I put a magnet on it once... but nothing happened

They kind of smell funny too if I recall correctly slightly burned smell
?!

Or is that the magnets I smelled ?

Is it possible to smell magnets ? maybe it's the metal smell what is
it made of anyway ?

Plastic plus what else ?

Older PC FDCs had a command where one could write deleted sectors, but
at some stage in "improvement" of ASICS (part of which the FDC is
emulated) that command got dropped (early in 586 production, so use an
original PC or 286, 386 or 486).
BTW, without the "deleted sector" command, the "newer" PCs can neither
read nor write them.

Could a C64 1541 drive read ms-dos/pc floppies ?

Bye,
Skybuck.

 

[Skybuck Flying]

Answer to last question:

Could a C64 1541 drive read ms-dos/pc floppies ?

http://www.zimmers.net/anonftp/pub/cbm/transfer/1541-dos/1541-dos.txt

It seems it involves modifications... which would ofcourse be way too risky
to do...

Maybe there is another way to read/write c64 disks on pc or vice versa
without hardware modifications ?

Otherwise I don't understand the initial excitement about his discovery...
maybe he tought it might work... he doesn't seem sure yet... (the dude from
the original link in first post )

Me trying to make sense of this all... does this sector layout solve
anything ?

Bye,
Skybuck.

 

[Martijn van Buul]

* Skybuck Flying:

Answer to last question:


http://www.zimmers.net/anonftp/pub/cbm/transfer/1541-dos/1541-dos.txt

It seems it involves modifications... which would ofcourse be way too risky
to do...

Maybe there is another way to read/write c64 disks on pc or vice versa
without hardware modifications ?

No, there is not; the controller is too stupid for that. There are
alternative controllers that aren't as braindead, but that's not 'without
hardware modifications'.

But what made you think this was the case here? Why would a C64 need to
read a PC floppy, or vice versa? The beauty of this trick is that it's not
required at all; a PC will 'see' a floppy with a whole lot of bad tracks
which it will just ignore, and the C64 will do just the same.

Otherwise I don't understand the initial excitement about his discovery...

It's a very clever trick, and elegant in a strange way. But I don't think
you'll be able to understand that.

Me trying to make sense of this all... does this sector layout solve
anything ?

It's not about sectors, dimwit, it's about tracks.

A C64 disk and a 360K PC disk are both 40 tracks, but that's where the
similarity ends. The whole reason this hack can exist is that a PC stores
volume information on track 0, including the file allocation table and
directory entries and what not, whereas the C64 does this on track 18.
What happens is that the PC will read it's info from track 0, and will see
that several tracks, including track 18, are 'bad', and it will just avoid
them, not realising that they really contain a C64 filesystem. The C64, on
the other hand, will start reading info from track 18, and will notice
that track 0 (which is just a 'normal' data track as far as a C64 is
concerned) is not available for storage, and will happily avoid reading it.

So there you have it: A disk which seems readable on both a C64 as well as
a PC. Of course, this will only work as long as both sides don't try to
access tracks 'of the other side', which would typically happen when you
try to copy a disk.

The comments clearly describes how it works, but I think you're just too
stoned to recognise that. Lay down those drugs.

(To alt.c64: where I write "C64 disk" and "C64", I obviously mean "1541
disk" and "1541" respectively, but I didn't want to complicate matters.
Skybuck won't be able to understand it as it is)

 

[Skybuck Flying]

Ok,

Now somebody with some programming experience AND a PC and a C64 make a nice
youtube video of it...

I wanna see some proof of it ! =D

^ Just for fun ^

Thanks for the explanation ! and yes I did not have much sleep last night !


Bye,
Skybuck.

 

[Skybuck Flying]

Ok,

Now somebody with some programming experience AND a PC and a C64 make a nice
youtube video of it...

I wanna see some proof of it ! =D

^ Just for fun ^

Thanks for the explanation ! and yes I did not have much sleep last night !


Bye,
Skybuck.

 

[Jaelani]

I can understand his excitement. Those kind of format is hard to make.
One would need to "hand-craft" it (track by track and sector by
sector) prior making a specialized software for it.

I don't know the details about C64 drive, but PC drive is very much
capable of producing any kind of formats as long as they support the
track density of the floppies which I suspect the same for C64 drive.

It's simply because floppy drives can be controlled almost in every
aspect which allows one to restructure the data on each track - making
it possible to do real low level formatting and restructuring the
sector layout and other finer details. It's not even close when
compared with so-called harddisk drive low level format because it has
far more greater control of the floppy drive hardware. CD-ROM writer
drives (for writing only) has a little more control than harddisk
drives.

Some parameters in track & sector structures are:
- Track & sector gaps
- Track & Sector synchronizations
- Sector IDs
- Sector Addresses (CHRNs)
- Sector CRC

Some sector IDs:
- Hidden Sector
- Unknown Sector
- Deleted Data Address Mark
- Bad CRC
- No Data Address Mark
- Long Gap
- Duplicate CHRN Record
- Short Data
- LA (unknown to me)

The above parameters are not just for low level formatting, but also
for general reading and writing. MS-DOS keeps a number of supported
IBM-PC disk formats and use it each time a new floppy is accessed.

I once tried to read my Atari 800XL single-sided, single-density (35
tracks/inch) 5.25 inch floppies (mine is equipped with an external
floppy drive) just out of curiosity and the drive really can read it.
The hard part at first was determining the Atari 800XL disk format
which I'm completely blind at that time. But thanks to a utility
called Rescue (from the same maker of Trans Copy), I can find out
about it and make a little utility to make a raw disk to image file
copier for the Atari floppies so that I can inspect the sector data
using a hex viewer. Of course, it just read and copy them sector by
sector without knowing what file-system it uses.

These information can be found in the IBM PC/XT Technical Reference
book. It's complete details of IBM PC/XT hardware including IBM PS/2
(in later revision). You'll be very lucky to get one of these since
it's very old and hard to find. Other very useful source is the Ralf
Brown Interrupt List which also contains a reference for hardware
ports (plus other references). In this case, it's the floppy disk
controller ports and the BIOS disk interrupts.

 

[Skybuck Flying]

On the websites in the comments section some write that C64 had variable
track or sector lengths or something like that.

If true then pc floppy drives would need to be able to do that to be able to
make such a floppy which some say the pc floppy drives/controllers cannot
do...

Otherwise it can only be done in partial steps to get the full floppy:

The PC makes the PC section on the floppy.
The C64 makes the C64 section on the floppy.

So then it would require at least two computers to make the floppy !

Bye,
Skybuck.