Floppy Disc Capacities [was Pictures of My Machine Room (So Far)]

Dave Dunfield dave06a at dunfield.com
Tue Jun 19 06:20:49 CDT 2007

> My first iteration of Windows 95 was on 3.5 inch floppy diskettes.  At
> some point, I wanted to make a backup copy on diskettes but couldn't
> because the file sizes of the Windows distribution floppies was
> 1.8-1.9MB each.  At the time I thought it was some sort of copy
> protection.  I assume they must have been able to format the discs for a
> higher capacity - close to 2MB.
> Does anyone know how?

Thats Microsofts DMF (Distribution Media Format) - smaller gaps, more
sectors (21/track iirc) - ImageDisk can copy them.

Smaller gaps mean less room to realign when writing sectors into an
existing track. DMF disks are OK for "Distribution Media" because they
are written one (presumably in a continuous track) and do not have to
be re-written on countless slightly varying drives...

Generally you can get more space on a disk by going with a larger sector
size (as long as size * #sectors works out to near the end of a track),
as this reduces the number of gaps you need. I recall a DOS TSR called
"2M" which got nearly 2 Megs of data on a disk by using big (2k iirc)


dave06a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:

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