Application and value of the serial port connector:An Asynchronous port on the computer used to connect a serial device to the computer and capable of transmitting one bit at a time. Serial ports are typically identified on IBM compatible computers as COM (communications) ports. For example, a mouse might be connected to COM1 and a modem to COM2. With the introduction of USB, FireWire, and other faster solutions serial ports are rarely used when compared to how often they've been used in the past. In the picture to the right is a close up of a DB9 serial port on the back of a computer.

Identifying

In the above graphic of a serial port you can notice the DB9 serial port connection is easy to identify. The connection is in the shape of the letter D, is a male connector, and has 9 pins.

Pin information

Below is a listing of each of the pins located on the DB9 connector and what each of these pins are for. As can be seen in the above picture pin one is in the top left and pin 9 is in the bottom right.

PIN PURPOSE SIGNAL NAME
1 Data Carrier Detect DCD
2 Received Data RxData
3 Transmitted Data TxData
4 Data Terminal Ready DTR
5 Signal Ground Gnd
6 Data Set Ready DSR
7 Request To Send RTS
8 Clear To Send CTS
9 Ring Indicator RI

What is the serial port used for?

Below is a listing of various hardware components that can be purchased and used with your serial port.

Mouse - One of the most commonly used devices for serial ports, usually used with computers with noPS/2 or USB ports and specialty mice.
Modem - Another commonly used device for serial ports. Used commonly with older computers, however, is also commonly used for its ease of use.
Network - One of the original uses of the serial port, which allowed two computers to connect together and allow large files to be transferred between the two.