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From: The Doctor on 26 Jan 2010 15:36
On 2010-01-26, Peter Dassow <z80eu(a)arcor.de> wrote:
> mrtinbspam(a)gmail.com wrote:
>> Imposible, as 1541 uses GCR-encoding, and PC-drives uses MFM-encoding.
>> Unfortunatly it cannot be overrided, as the MFM-encoding is done with
>> a chip on the PC.

Commodore uses FM but it takes advantage of the greater circumference of
the outter trackers in order to fit in more sectors. This means that
either the 1541 supported different drive speeds or (more likely) the
controller supported multiple baud rates with the R/W head.

> That's not the whole truth. There was a special disk controller named
> "Catweazle", which made it possible to write also GCR coded Apple II
> disk images for example.

Apple DOS 3.2 just used regular FM (i.e. it only used every other bit on
the disk) where as DOS 3.3 used it's own special 6:8 RLL encoding where a disk
byte held 6 bits of data instead of 4. I can only imganine what would
happen if Apple had also allowed higher baud rates for the outter tracks
and a full 40 tracks.

GCR is a error correction system for IBM tape drives.

(q.v. <URL:http://en.wikipedia.org/wiki/Run_length_limited>)

--
The Doctor
From: Rudolf Harras on 26 Jan 2010 17:05
The Doctor schrieb:

>>> Imposible, as 1541 uses GCR-encoding, and PC-drives uses MFM-encoding.
>>> Unfortunatly it cannot be overrided, as the MFM-encoding is done with
>>> a chip on the PC.
>
>Commodore uses FM but it takes advantage of the greater circumference of
>the outter trackers in order to fit in more sectors. This means that
>either the 1541 supported different drive speeds or (more likely) the
>controller supported multiple baud rates with the R/W head.

By the way: the 1571 can read DOS-Disks.
From: James on 26 Jan 2010 19:29
On Jan 26, 2:36 pm, The Doctor <doc...(a)localhost.localdomain> wrote:
> Commodore uses FM but it takes advantage of the greater circumference of
> the outter trackers in order to fit in more sectors. This means that
> either the 1541 supported different drive speeds or (more likely) the
> controller supported multiple baud rates with the R/W head.
>
> GCR is a error correction system for IBM tape drives.
>
> (q.v. <URL:http://en.wikipedia.org/wiki/Run_length_limited>)

Commodore used GCR on their floppy drives up to and including the
1571. Only the 3 1/2" drive (1581) used MFM. The format is documented
in the manual that came with a Commodore drive.

The Commodore GCR format is similar to the IBM GCR format:
http://en.wikipedia.org/wiki/Group_code_recording#GCR_for_floppy_disks
From: Christian Brandt on 27 Jan 2010 02:06
Am 26.01.2010 06:56, schrieb Jack Tseng:
> Can you find the DOS program that write the C1541 formatted disk in IBM 360K
> floppy drive from the D64 image? Like Writeatr.exe

You are looking for http://simonowen.com/fdrawcmd/ which can read many
native encoded formats in a simple PC drive.

Yes, you read this right: NO CATWEAZLE REQUIRED!!!

It bitbangs the �PD765a floppy controler and can read even strange
formats like old DD apple drives.

Christian Brandt
From: Tom Lake on 27 Jan 2010 05:48
> Commodore used GCR on their floppy drives up to and including the
> 1571. Only the 3 1/2" drive (1581) used MFM. The format is documented
> in the manual that came with a Commodore drive.

Not quite. The 1571 can read/write *both* CGR and MFM.

http://www.absoluteastronomy.com/topics/Commodore_1571

Tom Lake
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