| 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.
For many computer peripheral devices the USB interface has replaced the serial port — as of 2007, most modern computers are connected to devices through a USB connection. While nearly every server has a serial port, many modern low-end workstations and laptops often don't have one. The serial port is omitted for cost savings, and is considered to be a legacy port. Serial ports can also be found in industrial automation systems, scientific analysis, shop till systems and some industrial and consumer products. Network equipment (such as routers and switches) often have serial ports for configuration. Serial ports are still used in these areas as they are simple, cheap and allow interoperability between devices.
Some computers, such as the IBM PC, used an integrated circuit called a UART, that converted characters to (and from) asynchronous serial form, and automatically looked after the timing and framing of data. Very low-cost systems, such as some early home computers, would instead use the CPU to send the data through an output pin, using the so-called bit-banging technique.
The vast majority of personal computer motherboards still have at least one serial port. However some may only have a pin header, and a fly lead is required to bring the connector out through the case. Small-form-factor systems and laptops, however, often do not include them in order to conserve space. RS-232 has been standard for so long that the circuits needed to control a serial port became very cheap and often exist on a single chip, sometimes also with circuitry for a parallel port.
Early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS-232. Inter-operation with RS-232 devices may be impossible as the serial port cannot withstand the voltage levels produced and may have other differences that "lock in" the user to products of a particular manufacturer.
Low-cost processors now allow higher-speed serial communication standards such as USB and FireWire to replace RS-232. These make it possible to connect devices that would not have operated feasibly over slower serial connections, such as storage devices, sound devices, and video devices.
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