Any device connected internally or externally to a computer and used in the transfer of data to or from a computer. A personal computer (PC) or workstation processes information. Data (unprocessed information) must get into the computer, and the processed information must get out. Information is entered and displayed on a wide variety of accessory devices called peripherals, which are also known as input/output (I/O) devices. Some peripherals (such as keyboards) are only input devices, others (such as most printers) are only output devices, and some are both. Peripherals may be located inside or outside a computer's case (called an internal or external device, respectively). The I/O bus is the collection of circuits where an internal device is attached. An I/O port (such as parallel or serial port) is a connector where an external device is connected (plugged in).