RE: CBM-900 floppy disk format/encoding

Are you assuming they are not 1541 type format or do you know?
Do you know they are Commodore High Density?

I have a SFD 1001 and it used DS/DD diskettes, NOT HD (High Density)
diskettes.
That was the amazing thing about it, to fit that much on a non HD diskette.

Ed

-----Original Message-----
From: owner-cbm-hackers@musoftware.de
[mailto:owner-cbm-hackers@musoftware.de] On Behalf Of MikeS
Sent: Friday, October 21, 2011 7:10 PM
To: cbm-hackers@musoftware.de
Subject: Re: CBM-900 floppy disk format/encoding

Without knowing anything about the CBM-900 or even the SFD-1001 I'd say it's
No. 2)

From the specs below it looks like you should be using a 5.25"  *1.2MB HD*
disk drive, not a DS/DD (~360KB) drive.

mike

----- Original Message -----
From: "Uffe Jakobsen" <uffe@uffe.org>
To: <cbm-hackers@musoftware.de>
Sent: Friday, October 21, 2011 5:51 PM
Subject: CBM-900 floppy disk format/encoding


>
>
> Hi,
>
> I'm in the progress of dumping some 5.25" disks from a CBM-900 (protoype) 
> system - for "obvious" preservation reasons.
>
> The disks are labeled to contain Coherent 0.7.3 (UNIX) - (which was the OS

> for CBM-900)
>
> From the labels both "lowres" and "highres" Coherent disk sets exists.
> I guess that has to do with hw graphics modes and not the disk format.
>
>
> My problem is that I cannot read/dump the disks.
>
> I've even tried dumping with the Kryoflux unit (http://kryoflux.com)
> It does not recognise the disk either - and hence it can only produce a 
> "flux" preservation dump - which it a sort of recording of the magnetic 
> fluxuations on the disk surface.
>
> The fact that Kryoflux doesn't give me anything can mean a number of 
> things:
>
> 1) the disks are damaged - not very likely - the disks have been stored 
> correct all the years.
>
> 2) the drive I'm using with kryoflux (5.25" DS/DD 83 tracks) is not the 
> right type.
>
> 3) the disks are not encoded with either FM/MFM/GCR
>
>
>
> From various sources on the net I've read that the CBM-900 contains a 
> drive that is SFD-1001 compatible and an MFM disk controller.
>
> Quoting zimmers.net: (http://www.zimmers.net/cbmpics/c900.html)
>
> Addition hardware:
>     1.2 megabyte 5.25" disk drive (SFD-1001 compatible)
>     20 megabyte hard drive
>   C900 Series:    Prototype UNIX System, dropped after Amiga acquisition
>                 Zilog Z8000 CPU, Runs Coherent 0.7.3, UNIX 7 clone,
>                 Built-In Floppy, HD, IEEE-488. MFM Disk Controller, 1MB
>           9600 bps, 500 units made. Came in two versions.
>
> But what does the above actually mean ?
>
> 1) is it only the mechanical parts of the disk drive that is similar to 
> the SFD-1001 ? or does CBM-900 contain a complete SFD-1001 with comtroller

> board etc ? (I think not)
>
> 2) The MFM disk controller ? is it for the harddisk or the floppy or both 
> ?
>
> Could someone give me some info on what disk format/encoding to expect on 
> those Coherent disks.
>
> Now I could take the CBM-900 apart and have a look inside - but it is kept

> in a storage room - and is unaccessible at the moment.
>
> I'd be thankful for any information :-)
>
> Best regards
>
> /Uffe
>
>
>
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