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USB Parallel Serial Computer Ports

The input, ouput and communication devices are connected to the system unit through a special device called the port. It is an interface or connecting socket on the outside of system unit. It provides a standard way of communication between the computer and its input and output devices. For example, keyboard, mouse, monitor, printer, modem etc. come with a cable and a multiple connector. The device is linked with the computer by plugging its connector into a port. The term jack sometimes is used to identify audio and video ports.

The back of the system unit contains many ports. Some modern PCs also have ports on the front of the system unit. Ports have different types of connectors. A connector joins a cable to a device or peripheral. One end of the cable attaches to the connector on the system unit and the other end of the cable attaches to a connector on the device. The connectors are available of two types.

For example, a printer port might use 25-pin female connector or 36-pin female connector etc.

Types of Ports

A system unit may contain many ports of different types. The main type of ports are serial port, parallel port and USB port. Most personal computers have at least one serial port, one parallel port and two USB ports. The types of ports are described below.

1. Serial Port

A serial port provided a connection  for transmitting data one bit at a time. The data is serial port is transmitted one bit at a time through a single wire. However the serial port consists of multiple wires. The other wires control the flow of data. The COM port (communication port) on the system unit is one type of serial port. The IBM computers have maximum four serial ports, which are designated COM1, COM2, COM3 and COM4.

The transmitting of data through serial port is very slow because data is transmitted one bit at a time. The mouse, keyboard, modem etc. are connected to serial port. Modem is connected to the serial port because data through telephone line is communicated in a specific frequency.

Serial ports conform to either the RS-232 or RS-422 standard, which specifies the number of pins used on the ports connector. Two common connectors for serial ports are 9-pin male connector and 25-pin male connector.

2. Parallel Port

A parallel port provides a connection for transmitting data 8-bits at a time. The devices that are connected to the parallel port have a data cable with eight parallel separate data lines. The printer is connected to the parallel port. The cables used to connect printer to the computer through the parallel port often have 25-pin female connector. The IBM computes have maximum 3 parallel ports, which are designated LPT1, LPT2, LPT3. In most microcomputers LPT1 port is used as a standard parallel port. The transmitting of data through parallel ports is faster than serial port.

3. USB Port

USB stands for Universal Serial Bus. Today it is the most popular standard port used in PCs of both IBM compatible and Apple computers. The USB allows upto 127 devices to be connected to the bus via a single port. Today personal computers typically have 2 to 4 USB ports either on the front or back of the system unit. The USB hub is also available to connect multiple devices with a computer having a single USB port. A USB hub is a device, which is plugged into a USB port on the system unit and contains multiple USB ports into which you can plug multiple devices.

USB port also supports hot plugging and plug & play. It means that you can attach devices with a computer while computer is running. You have not to restart the computer after attaching the device.

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