Re: CBM-900 floppy disk format/encoding

Hi Groepaz,

On 2011-10-24 15:09, Groepaz wrote:
> On Sunday 23 October 2011, you wrote:
>> Hi Groepaz,
>>
>> On 2011-10-23 15:18, Groepaz wrote:
>>> On Sunday 23 October 2011, you wrote:
>>>> Given the fact that I've already tried dumping the disks with an 80
>>>> track drive (HD) - I'm leaning more to my own conclusion which is:
>>>>
>>>> I need to get hold of a 100 TPI floppy drive and try that with my
>>>> kryoflux.
>>>
>>> i dont know what kind of analysis stuff the kryoflux tools offer - but i
>>> can tell you that if it is the same format as used with the sfd1001,
>>> then you should be able to read *some* tracks correctly. the lowlevel
>>> encoding is the same gcr as found on 1541 (and all other cbm drives).
>>> you should be able to tell which lowlevel encoding is used by making a
>>> histogram of one track (again, no idea what the kryoflux tools let you
>>> do).
>>>
>>> and that said, 100tpi shugart drives seem to be extremely impossible to
>>> find these days. i'd rather look for a solution to read those disks with
>>> a PET or something :)
>>
>> I do have both SFD-1001 and CBM-8250 drives - but I doubt that the
>> format used for CBM-900 floppies is the CBM GCR encoded filesystem.
>>
>> I've come to the conclusion that it is only the mechanics that is
>> similar to SFD-1001.
>>
>> But I'm only guessing - later this week I'll be able to do more
>> investigations on the CBM-900 story.
>
> does the kryoflux software allow you to read a raw track and then display a
> histogram of the data? if so, try reading some of the first tracks of a disk,
> you should see either 2 (FM) or 3 (MFM/GCR) "peaks" in the histogram. if its
> the later, post the result and i can probably tell if its mfm or gcr :)
>

Sorry for my late answer,

Well, it does show a plot but only during the dump process - I cannot 
visualize the plot after the dump has ended - and I have no sccreenshot 
from the dump and no kryoflux here atm...

But I do have the raw track files - I haven't had the time to look into 
the format but it looks pretty raw to me - and the contents looks quite 
systematic if you ask me - as if the kryoflux actually got something out 
of the drive event though that I'm pretty sure that the drive used with 
the Kryoflux is the wrong TPI (96) where should be 100 TPI.

If want I can send you the contents (off list) of a single track and you 
could try have a look ? I guess that track 0 is the same pos for both 96 
and 100 TPI

Additional info: I did have time to fire up a CBM-8296 and CBM-8250 
drive - both in working contition. Couldn't read any dir from the 
CBM-900 disks with the CBM-8296. From the start I didn't expect the 
CBM-900 disks to be CBM-DOS GCR format. The CBM-8250 returned DOS error 
code 23 (checksum error in data block) stating that the right 
track/sector have been read into memory but that the checksum on the 
data is wrong. Right now I don't really know what to conclude from this...

/Uffe



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