Problem with Win32_PhysicalMedia SerialNumber property - wmi

Question

I wrote the following code to get the physical media serial number but in one of my computers it returns null instead.
Does anybody know what the problem is?
Thanks.
var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PhysicalMedia");
foreach( ManagementObject mo in searcher.Get() )
{
Console.WriteLine("Serial: {0}", mo["SerialNumber"]);
}

Answer 1

The Serial Number is optional, defined by the manufacturer, and for your device it is either blank or unsupported by the driver.
Virtually all hard drives have a serial number, but most USB-style Flash memory sticks do not (generally a cost issue). I would imagine most unbranded CD/DVD/BD discs would also be non-serialized.

Answer 2

Here is the code I used, the serial number somehow is returned raw with each pair of chars reversed (strange) and using Win32_PhysicalMedia gave different results if I ran the code as a user or an Administrator(more strange) - Windows 7 Ultimate, VS 2008 using VB only:
Function GetHDSerial() As String
Dim strHDSerial As String = String.Empty
Dim index As Integer = 0
Dim Data As String
Dim Data2 As String
Dim ndx As Integer
Dim query As New SelectQuery("Win32_DiskDrive")
Dim search As New ManagementObjectSearcher(query)
Dim info As ManagementObject
Try
For Each info In search.Get()
Data = info("SerialNumber")
Data2 = ""
For ndx = 1 To Data.Length - 1 Step 2
Data2 = Data2 & Chr(Val("&H" & Mid(Data, ndx, 2)))
Next ndx
Data = String.Empty
For ndx = 1 To Data2.Length - 1 Step 2
Data = Data & Mid(Data2, ndx + 1, 1) & Mid(Data2, ndx, 1)
Next
Data2 = Data
If Len(Data) < 8 Then Data2 = "00000000" 'some drives have no s/n
Data2 = Replace(Data2, " ", "") ' some drives pad spaces in the s/n
'forget removeable drives
If InStr(info("MediaType").ToString, "Fixed", CompareMethod.Text) > 0 Then
strHDSerial = strHDSerial & "Drive " & index.ToString & " SN: " & Data2 & vbCrLf
index += 1
End If
Next
Catch ex As Exception
strHDSerial = "Error retrieving SN for Drive "
msgbox(index.ToString)
End Try
Return strHDSerial
End Function