Select the density of the disk you wish to format. Most of the 3.5" and 5.25" disks produced in the last 5 years are high density (HD) disks. Older disks may only support the double density (DD) format. High density disks can be formatted as double density, but you will not be able to use the full 1.44 Mbytes or 1.2 Mbytes of space on the disk. The 800k disk format used by Macintosh floppy drives is not currently supported, and cannot be supported at all on PC floppy drives since they are not capable of formatting disks in that fashion.
Here is a list of the properties for each disk type and density combination:
3.5" DD: double-sided, 80 tracks, 9 sectors/track - 720K
3.5" HD: double-sided, 80 tracks, 18 sectors/track - 1440K
5.25" DD: double-sided, 40 tracks, 9 sectors/track - 360K
5.25" HD: double-sided, 80 tracks, 15 sectors/track - 1200K