Definition: USB hub

A device that increases the number of USB ports on a PC or Mac. USB hubs are typically used to extend USB sockets to the top of the desk to conveniently plug in USB drives, cameras and portable storage drives.

Self Powered vs. Bus Powered
Self-powered hubs derive their power from a wall outlet and usually provide up to 500 milliamps (mA) at each port. In contrast, bus-powered hubs obtain all their power from the one USB port they plug into. As a result, bus-powered hubs have to split the total 500 mA among all their ports, and the hub itself generally draws 100 mA. A four port bus-powered hub would have 100 milliamps of power at each port.

Keyboards and mice typically need less than 100 milliamps, but USB drives and external storage drives need more. When not plugged into an AC outlet, a self-powered hub may sometimes be able to function as a bus-powered hub.

USB Type C Is Changing the Game
Because USB Type C ports support higher current than Type A ports, bus-powered USB-C hubs can handle more devices (see USB Power Delivery and USB Type C). See USB switch, PoweredUSB and USB.

USB Hubs

The self-powered four-port hub (top right) only adds three Type A ports for the user because it uses the one in the computer it plugs into. Monitors and keyboards often contain a USB hub, which can be self or bus powered.

A Nine-Port USB Hub

This Anker port adds eight USB 3.0 ports to the computer.