serial port, what is serial port, how serial port works
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What is serial port and how it works?

In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time (contrast parallel port). Throughout most of the history of personal computers, data transfer through serial ports connected the computer to devices such as terminals and various peripherals.

While such interfaces as Ethernet, FireWire, and USB all send data as a serial stream, the term "serial port" usually identifies hardware more or less compliant to the RS-232 standard, intended to interface with a modem or with a similar communication device. They are 9-pin connectors that relay information, incoming or outgoing, one byte at a time. Each byte is broken up into a series of eight bits, hence the term serial port.

Serial ports are one of the oldest types of interface standards. Before internal modems became commonplace, external modems were connected to computers via serial ports, also known as communication or "COM" ports. Computer mice and even keyboards also used serial ports. Some serial ports used 25-pin connectors, but the 9-pin variety was more common. Serial ports are controlled by a special chip call a UART, Universal Asynchronous Receiver Transmitter.

Serial ports differ from 25-pin parallel ports in that the parallel ports transmit one byte at a time by using eight parallel wires that each carry one bit. With data traveling in parallel, the transfer rate was greater. A parallel port could support rates up to 100 kilobytes per second, while serial ports only supported 115 kilobits per second (kbps). Later, enhanced technology pushed serial port speeds to 460 kbps.

In modern personal computers the serial port has largely been replaced by USB and Firewire for connections to peripheral devices. Many modern personal computers do not have a serial port since this legacy port has been superseded for most uses. Serial ports are commonly still used in applications such as industrial automation systems, scientific analysis, shop till systems and some industrial and consumer products. Server computers may use a serial port as a control console for diagnostics. Network equipment such as routers and switchesoften use serial console for configuration. Serial ports are still used in these areas as they are simple, cheap and their console functions are highly standardized and widespread. A serial port requires very little supporting software from the host system.

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