Because a particular USB port can only support so much current. A powered hub provides the power for all of its connected ports. An unpowered hub is subject to the limits of the single port its connected to.
Because a particular USB port can only support so much current. A powered hub provides the power for all of its connected ports. An unpowered hub is subject to the limits of the single port its connected to.
Or at least up to the capacity of the hub's "wall wart" power pack.
Note that some USB peripherals, like printers, tend to have their own
power sources. It's USB items like keyboards, game controllers,
mice/trackballs, memory devices (camera memory card readers and thumb
drives) and some PDA adaptors that use the port's power.
