How to read Osborne 1 Floppies?

Tom Hunter ccth6600 at
Tue May 25 08:41:54 CDT 2021

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>

> 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