What Is a D-Sub Port?

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Older printers require a 25-pin D-Sub port for connection.

D-Sub ports are used for connecting external devices to a computer. They are an older method of connection, but some modern computers still contain them. These ports are gradually being replaced by more efficient connection technology, such as USB and Thunderbolt.


Computer Ports

A port is an electrical connection point on the outer surface of a computer case. Ports connect devices directly to the motherboard, or main circuit board, of a computer. Common devices that use ports are a monitor, mouse, keyboard and printer. Some ports connect a specific device, such as the VGA port for a monitor. Others, including USB ports, are "general-purpose" and can connect various devices, such as cameras, joysticks and cell phones.


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D-Sub Connectors

The term "D-Sub" stands for "D-Subminiature," which is a type of connector. D-Sub connectors were created in the 1950s, and they are still used in modern computers. They are shaped like a sideways letter "D," with one side slightly longer than the other. Due to the shape, there is only one way to connect a device. All D-Sub connectors have a metal "shield" that surrounds two or more rows of pins (male) or holes (female). The number of pins or holes in D-Sub connectors can range from nine to 100.


Advantages and Disadvantages

One advantage to some D-Sub ports is that they contain threaded holes on each side that secure the screws on male D-Sub cables. This creates a solid and reliable connection. Other advantages are that the multi-pin ports allow for many wiring options and the connectors are inexpensive. The disadvantages are that the ports are large and do not contain wires or lines for power. The D-Sub port has lines for data and communication, but a connected device still requires a separate power supply. USB ports have replaced D-Sub ports because they are much smaller, wiring is more consistent and they do contain lines for powering devices.


Common D-Sub Ports

Two types of D-Sub ports are still in use. The first is the VGA, or monitor, port. It is a female D-Sub connector that contains a flat surface and fifteen holes divided into three rows. The second is the 9-pin, or DE-9, serial port. It is a female D-Sub connector that contains nine holes divided into two rows. It is called "serial" because data is transferred and received one "piece" at a time over two lines. The 9-pin serial port is a general-purpose port, and it is the type of D-Sub that has largely been replaced by the USB port.