Whenever a disk is formatted, the operating system writes a serial number onto it.  This number is not guaranteed to be unique, but as it is a 32 bit integer it is unlikely to find a duplicate!  The number is often used as part of a copy protection system.  This tip shows you how to retrieve the number. Declarations Copy this code into the declarations section of the project. Private Declare Function GetVolumeInformation Lib _ "kernel32.dll" Alias "GetVolumeInformationA" (ByVal _ lpRootPathName As String, ByVal lpVolumeNameBuffer As _ String, ByVal nVolumeNameSize As Integer, _ lpVolumeSerialNumber As Long, lpMaximumComponentLength _ As Long, lpFileSystemFlags As Long, ByVal _ lpFileSystemNameBuffer As String, ByVal _ nFileSystemNameSize As Long) As Long Code Function GetSerialNumber(strDrive As String) As Long     Dim SerialNum As Long     Dim Res As Long     Dim Temp1 As String     Dim Temp2 As String     Temp1 = String$(255, Chr$(0))     Temp2 = String$(255, Chr$(0))     Res = GetVolumeInformation(strDrive, Temp1, _     Len(Temp1), SerialNum, 0, 0, Temp2, Len(Temp2))     GetSerialNumber = SerialNum End Function Use An example of using the above function: Call MsgBox GetSerialNumber("C:\") This will bring up a message box with the serial number of the C drive.