The D-sub monitor input has 15 pins arranged in three rows that carry video signals from a computer’s graphic display device to a monitor. The term D-sub refers to the D-shape of the connectors and the size (sub-miniature). Most D-sub connectors support VGA, which is the analog video signal standard.
D-sub monitor inputs include a female port on the computer for graphic display output, a cable, and a corresponding male port on the monitor. Commercial cables have a molded connector on each end, one male and one female, each with a D-shaped metal shield and three rows with five pins each. The port on the computer uses a female socket, while the port on the monitor uses a male socket. Two thumbscrews on either side of the cable plugs provide strain relief and secure the cable in the respective ports. The D-shapes ensure correct plug orientation. Other types of ports and cables also use the D-shaped connection design but have many more pin and socket connections and layouts.
Introduced by IBM in the late 1980s, the D-sub was small compared to other computer ports, so the term sub-miniature made sense at the time. As digital video signals replaced analog signals, other cable designs such as HDMI have since eclipsed the D-sub.