How to read Osborne 1 Floppies?

Peter Coghlan cctalk at
Tue May 25 13:22:46 CDT 2021

Early on, floppy disks on the BBC Micro were 5.25in FM with 10 sectors
per track and 256 bytes per sector.  However, BBC Micros are probably not
common where you are and some programming in 6502 assembly or BBC Basic
and a knowledge of the Osbourne filesystem would be required.

I might be persuaded to offer the use of a BBC Micro and to do the
programming if it is feasable to send me the disks and details of the
filesystem involved, assuming a more convenient solution doesn't come

Peter Coghlan.

Zane Healy wrote:
> Yes, we need to be able to access the files.
> I’m going to see if my old 486 will still boot up, I know I used to
> use it with imaging RX50 floppies.  I’m not an x86 collector, so
> have a pretty limited selection of PC Hardware.  I’m on my Sabbatical
> right now, so this request came in at a good time.  Though first I have
> to finish up on some VAX and Alpha systems I’m working on, so as to
> free up space.  That or finish a cleaning project in my office. :-)
> The cleaning project is needed to finish the VAX/Alpha projects…
> Is there any chances of reading these with Commodore 128 running CP/M, or
> a Kaypro 2?  The Kaypro is definitely on my “project list”, it
> worked last time I played with it.  I *might* have a DEC Rainbow, or
> I might have given it away.  If I do, I have no idea of its condition.
> An Apple //e would be another old system with 5.25” drives, but seems
> more unlikely.  I might still have an old Kaypro PC, though it hasn’t
> been used since ’94 (and there is a good chance it went to LCM).
> My focus is DEC and Commodore, though I do have a lot of Apple // gear.
> Zane
>> On May 25, 2021, at 9:38 AM, Fred Cisin via cctalk <cctalk at>
>> wrote:
>> Imagedisk is great for making images.
>> BUT, the original request is not for images, it is for the previous owned
>> wanting access to be able to use the content of the FILES that are in those
>> images.
>> On Tue, 25 May 2021, Tom Hunter wrote:
>>> Dunfield's ImageDisk reads and writes them just fine on most older PCs with
>>> a decent floppy controller.
>>> As Chuck G writes "TestFDC" will tell you if the floppy controller is
>>> usable for imaging.
>>> Best regards
>>> Tom Hunter
>>> On Tue, May 25, 2021 at 2:26 AM Fred Cisin via cctalk <cctalk at>
>>> wrote:
>>>> There were two Osborne floppy formats.  Both CP/M.
>>>> IIRC, the original format was "Single Density" (FM), 10 sectors per track,
>>>> with 256 bytes per sector (similar to the TRS80-Model-1.  That will
>>>> require FM/SD capability.  Most NEC FDCs did not support that.  Dave
>>>> Dunfield has a test program that will tell you whether your FDC can handle
>>>> it.
>>>> Then, they switched to "Double Density" (MFM) IIRC: 5 sectors per track,
>>>> with 1024 bytes per sector.  Any PC FDC with access to INT13h and INT1Eh
>>>> will work with appropriate software.  (NOT external USB drives)
>>>> WITH appropriate software, a flux transition device, such as your
>>>> Catweasel, could do it.
>>>> On Mon, 24 May 2021, Zane Healy via cctalk wrote:
>>>>> A photographer I know contacted me last night asking about reading
>>>> Osborne 1 floppies.  What does it take to read these?
>>>>> The only Catweasel board I have is the old Zorro 2 board for the Amiga.
>>>> I do have 5.25” floppy drives.  Neither of us have an Osborne anymore (I
>>>> think mine went to Jim Willing).
>>>>> Zane

More information about the cctech mailing list