Format.com Hidden Parameters

FORMAT drive: /AUTOTEST
Checks the existing format of your disk, and then proceeds with an unattended disk format.  It does not prompt for a volume label, it does not prompt to format another disk, no delay, no user intervention, ends without pausing, and displays disk space statistics after completion.

FORMAT drive: /BACKUP
This parameter works exactly like /AUTOTEST, but it does prompt the user for a volume label, and it does display disk space information upon completion.

FORMAT drive: /SELECT
This parameter is similar to using the MIRROR command (MS-DOS 5.0 and earlier only).

FORMAT drive: /U
This parameter performs an unconditional format, which destroys every byte of data on a disk by overwriting it with hex F6h. You cannot unformat a disk formatted using the /U option.

FORMAT drive: /SELECT /U
This particular combination of format.com parameters makes a disk. Do not use these two format switches together on any drive!

FORMAT drive: /Z:n
Formats a FAT32 drive with a cluster size of n times 512 bytes. Meaning:
drive: = your hard drive letter (C:, D:, E:... etc).
n = number of sectors per cluster multiplied by 512 (cluster size in bytes).
Examples:
n = 1    creates a 512 bytes cluster;
n = 2    creates a 1024 bytes (1 KB) cluster;
n = ?    creates a ? x 512 = ???? bytes (???? bytes : 1024 = ? KB) cluster.
You can modify the size of the allocation units (sectors) on a FAT32 drive to your heart's desire.