Each I/O device connected to your computer is mapped to a unique I/O (Input/Output) address. These addresses are assigned to every I/O port on your computer, including USB, Firewire, Ethernet, VGA, and DVI ports, as well as any other ports your computer might have.
Having a unique address assigned to each port allows your computer to easily recognize and locate devices attached to your computer. Whether it is a keyboard, mouse, monitor, printer, or any other device, the computer can locate it by its I/O address. Because I/O addresses are controlled by the computer's motherboard, they do not use up any system memory, or RAM.