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

Jaelani wrote:

> 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 wrote:
>
>>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.
Yea, but... the FDC emulation in the ASICs of modern PCs (read:
virtually all Pentiums) does NOT suport deleted data records.
Now you can write the software for reading and/or writing deleted
records, but these FDCs simply do not support the commands and nothing
seems to happen.
I used to write "copy protection" software where data and programs
were in the FAT and directory, used deleted records, and records with
absurd track/sector numbers - so i might know a little about such things.
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