For connecting up to 4 usb devices eg a mouse keyboard printer usb memory stick to a usb port topside socket allows you to plug usb devices in on the top for added simplicity and convenience bus powered ie power supply via the usb socket of a pcnotebook integrated usb cable for connection with a pcnotebook suitable and tested for usb 20 downward compatible with usb 11 system requirements operating system windows 1087vistaxp and mac os 10x