The input/output or I/O section permit the computer to take in data from the outside world or send data to the outside world. Peripherals such like keyboards, printers, video display terminals, and modems are connected to the I/O section. These permit the user and the computer to communicate with each other. The real physical devices utilized to interface the computer buses to external systems are frequently called ports. An input port permits data from a keyboard, an A/D converter, or some other source to be read to the computer under control of the CPU. An output port is utilized to send data from the computer to some peripheral, such like a video display terminal, a printer, or a D/A converter. Physically, the simplest kind of input or output port is just a set of parallel D flip-flops. If they are being utilized as an input port, the D inputs are associated to the external device, and the Q outputs are linked to the data bus, which runs to the CPU. Data shall then be transferred through the latches when they are enabled by a control signal from the CPU. In a system where they are being utilized as an output port, the D inputs of the latches are connected to the data bus, and the Q outputs are linked to some external device. Data sent out on the data bus by the CPU shall be transferred to the external device while the latches are enabled by a control signal from the CPU.