The sockets that let you daisy-chain numerous USB devices make up a hub. The two rectangular connectors found at the rear of your PC are known as the root hub. Other hubs may connect to the root hub either as built-in components of a monitor, keyboard, or other USB device, or as dedicated, stand-alone devices.

Dedicated hubs come with clusters of two, four, or more additional sockets. Once youÆve experienced the ease of plugging and unplugging USB devices from a hub on your desktop, youÆll never want to deal with serial and parallel ports again.

You canÆt simply attach devices to any port, however. USB ports deliver electricity as well as data to peripherals. Just as all devices attached to a root hub must share its 12 mbps of bandwidth, they must share a finite amount of electrical power. You need to plan your USB setup around the energy needs of your USB devices.

Bus-powered hubs draw power from the incoming USB connector and can output up to 100 milliamps per port. Self-powered hubs draw electricity from their own power cord (or from the PC, in the case of the root hub or PCI-to-USB adapter) and provide up to 500 mA per port. A single low-power peripheral, such as a keyboard or mouse, typically uses 25 to 40 mA, and a 100-mA port on a bus-powered hub easily accommodates it. Power-hungry devices such as cameras and hubs must be attached to the 500-mA port of a self-powered hub. Before you buy a USB peripheral, make sure your USB hub can meet its power needs.

If your attached USB peripherals draw more current than the bus can support, the entire bus may shut down. To see whether your USB peripherals are drawing more current than the bus can support, look for a warning icon next to the Universal Serial Bus controller entry in WindowsÆ Device Manager. Aside from the warning icon, the only signal youÆll get that an overload has occurred is the malfunction of one or more USB devices.