And right they are. The USB port doesn't have the required bandwidth to be able to push a full video image like a synchronised computer display. A display like on the Tecra M4 and Portegé M200 ( 1400x1050x32bpp )requires 2.63 gigabit ( Gbit ) for an uncompressed stream at 60Hz refresh. A USB-2 interface has a theoretical peak of 480 megabit ( that's 0.47 gigabit ) theoretical peak value, whereas the practical throughput is generally much lower.