In a PC, the name assigned to the first serial port. The second is COM2, etc. PCs are typically designed to support up to four serial ports. On earlier PCs, two external serial ports were provided to connect a mouse and modem. On newer PCs, there is often only one external serial port as mice use a separate PS/2 port, and modems are generally built in and use an internal serial port. The term originated before the days of the mouse, when the serial port was primarily used for modem COM-munications. Contrast with LPT1.