Volume Serial Numbers

A volume serial number, sometimes seen as VSN, is a unique hexadecimal number assigned to a drive during the creation of the file system during the format process.

It's stored in the disk parameter block part of the volume boot record.

Microsoft and IBM added the VSN to the format process in 1987 when they were working together to develop the OS/2 operating system.

How Is the Volume Serial Number Generated?

It's created based on a fairly complex combination of the year, hour, month, second, and hundredth of a second that the drive was formatted. This means it will change each time the drive is formatted.

How to View a Drive's Volume Serial Number

One of the easiest ways to view the volume serial number is through Command Prompt, using the vol command. Execute it without any options, and you'll see both the volume serial number and the volume label.

vol

Duplicate Volume Serial Numbers

Since volume serial numbers aren't generated at random and without knowledge of the volume serial numbers on other drives in the computer, there's a chance two drives on the same computer could end up having the same volume serial number.

While this is technically possible, the chance is infinitesimally small and isn't usually a concern.

The only somewhat common reason why you might run into two drives in the same computer with identical volume serial numbers is when you've cloned one drive to another and are using them both at the same time.

Are Duplicate Volume Serial Numbers a Problem?

No, they're not a problem for Windows or other operating systems. Windows will not be confused as to which drive is which if two drives share volume serial numbers.

In fact, the VSN is used by some software licensing schemes to make sure that an installed copy of the software is being used on the correct computer. When cloning a drive, and the volume serial number remains, it helps ensure the software you run on the new drive works as you'd expect.

Another piece of data called the disk signature, part of the master boot record, is the truly unique identifier for a hard drive in a computer system.

Changing a Drive's Volume Serial Number

While there's no built-in ability in Windows to change a drive's volume serial number, some free vendor tools will do the trick.

Your best choice is probably Volume Serial Number Changer, a free, open-source program that shows you some basic information about your hard drive, plus a small field to enter the new number you want to set.

Another option is Volume Serial Number Editor. This program is similar, but it isn't free.

Advanced Reading on Volume Serial Numbers

To learn more about how volume serial numbers are generated, or how you might be able to tell something about a formatted drive by deciphering the number, check out this Digital Detective whitepaper: Volume Serial Numbers and Format Date/Time Verification.

There's more in that paper about the history of the volume serial number, as well as how to view it directly from the boot sector.