Direct cable connection to a standard serial cable) must be used to connect each of the two computers to communicate properly. Such connection uses PPP protocol. If the parallel ports are used, Windows supports standard or basic 4-bit cable (commonly known as LapLink cable), Enhanced Capabilities Port (ECP) cable, or Universal Cable Module (UCM) cable (which was known as DirectParallel cable by Parallel Technologies). Infrared communication ports, like the ones found on laptop computers (such as IrDA), can also be used. Connecting any two computers using USB requires a special proprietary bridge cable. A directly connected pin-to-pin USB type A cable does not
Serial port a 9-pin D-subminiature connector is not sufficient to indicate the connection is in fact a serial port, since this connector is also used for video, joysticks, and other purposes. Some miniaturized electronics, particularly graphing calculators and hand-held amateur and two-way radio equipment, have serial ports using a phone connector, usually the smaller 2.5 or 3.5 mm connectors and use the most basic 3-wire interface. Many models of Macintosh favor the related RS-422 standard, mostly using German mini-DIN connectors, except in the earliest models. The Macintosh included a standard set of two ports for connection to a printer and a modem,