Microsoft → [Info] Format c: /q /u ?

What exactly this does command do in Windows? I know that the /q command means it will format using the quick method but what does /u do?

/U
Specifies an unconditional format of a disk. Unconditional formatting destroys all existing data on a disk and prevents you from later "unformatting" the disk. You should use /U if you have received read and write errors during use of a disk.

/? displays help for most dos commands...

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M | M:\ | (2303528960 Bytes)
0:44:37 | Sun 2/03/08 |
-=}format /?

Formats a disk for use with Windows.

FORMAT volume [/FS:file-system] [/V:label] [/Q] [/A:size] [/C] [/X] [/P:passes]
FORMAT volume [/V:label] [/Q] [/F:size] [/P:passes]
FORMAT volume [/V:label] [/Q] [/T:tracks /N:sectors] [/P:passes]
FORMAT volume [/V:label] [/Q] [/P:passes]
FORMAT volume [/Q]

volume Specifies the drive letter (followed by a colon),
mount point, or volume name.
/FS:filesystem Specifies the type of the file system (FAT, FAT32, NTFS,
or UDF).
/V:label Specifies the volume label.
/Q Performs a quick format. Note that this switch overrides /P.
/C NTFS only: Files created on the new volume will be compressed
by default.
/X Forces the volume to dismount first if necessary. All opened
handles to the volume would no longer be valid.
/R:revision UDF only: Forces the format to a specific UDF version
(1.02, 1.50, 2.00, 2.01, 2.50). The default
revision is 2.01.
/D UDF 2.50 only: Metadata will be duplicated.
/A:size Overrides the default allocation unit size. Default settings
are strongly recommended for general use.
NTFS supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K.
FAT supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,
(128K, 256K for sector size > 512 bytes).
FAT32 supports 512, 1024, 2048, 4096, 8192, 16K, 32K, 64K,
(128K, 256K for sector size > 512 bytes).

Note that the FAT and FAT32 files systems impose the
following restrictions on the number of clusters on a volume:

FAT: Number of clusters --

Edit: Looks like /U isn't documented. Probably for the user's safety MS knows best.
Insanity is living in a state of disillusion.

My guess is that /U does nothing in modern systems but is accepted for back-compatibility.

In a system long ago and far away, the normal behaviour of format on a formatted volume was to save a copy of the FAT (or something) on the disk where it could be retrieved by the 'unformat' command, and /u meant "don't do that". Today, there is no 'unformat' command. A format is forever

It seems you are correct and there is no need for the /u switch anymore... I found this:

"My understanding is that the /U (unconditional) paramter became redundant starting with DOS 7.x and was disabled with ME. Prior to this DOS provided the UNFORMAT command, which was coupled to whether a FORMAT /U had been done or not. When the UNFORMAT command was dropped there was no need for the /U option and all formats became "unconditional". The /U continued to be accepted, but was effectively ignored."

»discussions.virtualdr.co ··· 488.html

I also heard a rumor that using the /u switch actually wipes out the drive with all zeros, is this true? The reason I'm asking is because, normally when I do a clean install of Windows XP, I do a Quick Erase using DBAN but since DBAN doesn't have the ability to work with floppy disks I have no way of zeroing out them after I'm done using them. I rarely use them but would like to be able to zero them out after I'm done using them for a particular task. I think KillDisk does this but I'm not sure, in terms of letting you zero out a floppy disk.

Don't know - but if you care, try it and see. Fill a floppy full of stuff, 'format' it with and without /u, and see what the floppy looks like afterwards. Something like winhex should do the job.

When the u switch was supported it did, yes. I have no idea whether it still does if you specify it.