Go to Start - select Run and then type in: CMD
In the black dialog box
type format/?
This gives you the list of available Commands.
There isn't a "u" but there is a "v" which is for label.
Hope this explains it.
Also, the U means that no format-reversal data is saved
or anything as some formatters will do. It's permanent
and there are not warnings, recovery info, or anything
else saved. Some formatters will allow you to recover
from a formatted disk and "unformat" it.