Volume Serial Number

A volume serial number is created based on a fairly complex combination of the year, hour, month, second, and hundredth of a second that the drive was formatted. VSN will change each time the drive is formatted.

Since volume serial numbers are not generated at random and without knowledge of the volume serial numbers on other drives in the computer, there's a chance that two drives on the same computer could end up having the same volume serial number. However, the chance is infinitesimally small and isn't considered a concern.

A drive's volume serial number is not the same as the manufacture serial number of the drive.

C:\>vol
 Volume in drive C has no label.
 Volume Serial Number is A000-DC1E

C:\>vol d:
 Volume in drive D is DATA
 Volume Serial Number is F9AC-F19C

Reference:
http://pcsupport.about.com/od/termsv/g/volume-serial-number.htm
http://pcsupport.about.com/od/commandlinereference/p/vol-command.htm
http://www.wildpackets.com/support/activation_faqs