A device that increases the number of USB ports on a PC. However, since the hub plugs into one of the USB ports on the computer, the total number of additional ports is minus one. For example, a four-port hub adds three new ports. USB hubs are typically used to extend USB sockets to the top of the desk for conveniently connecting external peripherals.|
Self Powered Vs. Bus Powered
Self-powered hubs derive their power from a wall outlet and usually provide up to 500 milliamps at each port. In contrast, bus-powered hubs plug only into the computer's USB bus and obtain all their power from the bus. As a result, they have to split the total 500 milliamps among all the ports and the hub itself, which generally draws 100 milliamps. For example, a four port bus-powered hub would have 100 milliamps of power at each port. When not plugged into an AC outlet, a self-powered hub may sometimes be able to function as a bus-powered hub.
Keyboards and mice typically need less than 100 milliamps, but USB drives and external hard disks need more. See USB switch, PoweredUSB and USB.
Note the self-powered hub at top right. It adds three Type A ports to the computer. Although it provides four Type A ports for devices, it already takes up one on the computer, netting three additional. Monitors may also contain a USB hub, which can be self powered or bus powered.