Visual Basic - Ayuda Urgente

hola necesito a ver si me pueden ayudar quisiera saber como hago para saber cuando un disco es de 512 o 256 o 1gb no se si se saca con una formula, favor si me pueden ayudar gracias........

Private Declare Function GetDiskFreeSpaceEx Lib "kernel32" Alias "GetDiskFreeSpaceExA" (ByVal lpRootPathName As String, lpFreeBytesAvailableToCaller As Currency, lpTotalNumberOfBytes As Currency, lpTotalNumberOfFreeBytes As Currency) As Long

Private Sub Form_Load()
Dim r As Long, BytesFreeToCalller As Currency, TotalBytes As Currency
Dim TotalFreeBytes As Currency, TotalBytesUsed As Currency

Const RootPathName = "C:\"

Call GetDiskFreeSpaceEx(RootPathName, BytesFreeToCalller, TotalBytes, TotalFreeBytes)

Me.AutoRedraw = True
Me.Cls
Me.Print
Me.Print " Total Number Of Bytes:", Format$(TotalBytes * 10000, "###,###,###,##0") & " bytes"
Me.Print " Total Free Bytes:", Format$(TotalFreeBytes * 10000, "###,###,###,##0") & " bytes"
Me.Print " Free Bytes Available:", Format$(BytesFreeToCalller * 10000, "###,###,###,##0") & " bytes"
Me.Print " Total Space Used :", Format$((TotalBytes - TotalFreeBytes) * 10000, "###,###,###,##0") & " bytes"
End Sub

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bueno ahi una forma , y en el link de abajo tenes otro ejemplo suerte

http://www.recursosvisualbasic.com.ar/htm/listado-api/170-mostrar-unidad-en-forma-grafica.htm