INT 2F - CD-ROM - READ VTOC
        AX = 1505h
        ES:BX -> 2048-byte buffer
        CX = drive number (0=A:)
        DX = sector index (0=first volume descriptor,1=second,...)
Return: CF set on error
            AX = error code (15=invalid drive,21=not ready)
        CF clear if successful
            AX = volume descriptor type (1=standard,FFh=terminator,0=other)