The cmdGo_Click event handler calls GetDiskFreeSpaceEx to load information into a LARGE_INTEGER structure that has low and high order words. Function LargeIntegerToDouble converts the values into Doubles.

Private Sub cmdGo_Click()
Dim bytes_avail As LARGE_INTEGER
Dim bytes_total As LARGE_INTEGER
Dim bytes_free As LARGE_INTEGER
Dim dbl_total As Double
Dim dbl_free As Double

    ' Get the space values.
    GetDiskFreeSpaceEx txtVolume.Text, bytes_avail, _
        bytes_total, bytes_free

    ' Convert values into Doubles.
    dbl_total = LargeIntegerToDouble(bytes_total.lowpart, _
        bytes_total.highpart)
    dbl_free = LargeIntegerToDouble(bytes_free.lowpart, _
        bytes_free.highpart)

    lblTotal.Caption = FormatBytes(dbl_total)
    lblFree.Caption = FormatBytes(dbl_free)
    lblUsed.Caption = FormatBytes(dbl_total - dbl_free)
    lblPercentTotal.Caption = Format$(1, "percent")
    lblPercentFree.Caption = Format$(dbl_free / dbl_total, _
        "percent")
    lblPercentUsed.Caption = Format$((dbl_total - dbl_free) _
        / dbl_total, "percent")
End Sub

' Convert a LARGE_INTEGER structure into
' data type to a Double.
Private Function LargeIntegerToDouble(low_part As Long, _
    high_part As Long) As Double
Dim result As Double

    result = high_part
    If high_part < 0 Then result = result + 2 ^ 32
    result = result * 2 ^ 32

    result = result + low_part
    If low_part < 0 Then result = result + 2 ^ 32

    LargeIntegerToDouble = result
End Function