Embedded DOS Volumes

The DOS 3.3 file format is wonderful for 140K 5.25" floppies, but requires some modifications before it will work on other kinds of media.  A number of authors came up with ways of putting one or more DOS 3.3 volumes onto an 800K floppy.  CiderPress recognizes most of them automatically.

Apple shipped two 3.5" drives, the AppleDisk 3.5 and the UniDisk 3.5.  The latter, combined with an interface card, would work on an Apple //e, and is responsible for the suffix used in some of the product names.

ProSel Uni-DOS (Glen Bredon)

ProSel-8 and -16 shipped with Uni-DOS, a way to format an 800K disk with 600K of space for ProDOS and 200K of space for DOS 3.3.  The embedded volume had 50 16-sector tracks.

DOS Master (Glen Bredon)

Essentially an enhanced version of Uni-DOS, DOS Master allowed placement of multiple DOS volumes on a single disk.  You could, for example, put five 140K DOS 3.3 disks on one 800K disk, and switch between them with the ",v" (volume) parameter.  The volumes could also be placed on a hard drive.

AmDOS 3.5 (Gary Little)

The "Amateur Disk Operating System version 3.5" software allowed storing two 400K DOS volumes on one 800K floppy.  Each DOS volume used 50 tracks of 32 sectors, which is the largest you can get without making significant alterations to DOS.  The change from 16 to 32 sectors broke compatibility with some programs (such as the "FID" file copying utility), but was manageable with a few well-placed patches.

UNIDOS (Unknown)

The disk format is identical to AmDOS.  It's unclear what the heritage of this is.

OzDOS (Richard Bennett)

This is another two-400K-disks-on-one-800K scheme, but the author decided to do something a little different.  Instead of putting the volumes one after the other, he stretched them out across the entire disk, using odd sectors for one volume and even sectors for the other.  For a device that reads 512-byte blocks, this makes a certain kind of sense.