COM (hardware interface)

COM, short for serial communication port, is a legacy interface used in computing for serial communication. It's a physical interface on a computer, often implemented as a DE-9 connector (though other connector types have existed). Historically, COM ports were a common way to connect peripherals such as modems, serial mice, and printers to a computer.

The COM port operates by transmitting data serially, meaning one bit at a time, over a single wire (plus ground). This is in contrast to parallel communication where multiple bits are sent simultaneously over multiple wires. Serial communication requires less cabling than parallel communication, but it's typically slower.

The most commonly used standard for serial communication over a COM port is RS-232. This standard defines the electrical signaling, data transmission rates, and connector specifications. However, other standards, such as RS-422 and RS-485, are also sometimes used with COM ports for improved noise immunity or longer distances.

Although largely superseded by faster and more versatile interfaces like USB, COM ports still find use in embedded systems, industrial equipment, and legacy devices where backward compatibility is essential. Virtual COM ports, implemented through USB or other interfaces, allow legacy applications designed for serial communication to interact with modern devices. These virtual COM ports emulate the behavior of a physical COM port in software. The operating system manages the interaction between the emulated COM port and the underlying physical interface.