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computer connectors

The six cable connectors pictured above are, from left to right, HP-type power connector, D-submineature 15 VGA connector, DB-25 Female printer connector, DIN type keyboard connector, DB-9 serial mouse connector and DB-15 joystick connector. None of these connector looks precisely alike and none fits correctly into a socket designed for another. This makes putting the cables back on to a computer nearly foolproof! Neat trick.

serial mouse parallel printer

Connectors have gender and can be male or female. Male contacts slide into a hole. Female contacts take in the male contacts. Thus, the serial mouse (DB-9) connector is a female connector while the DB-15 joystick connector is male. Male also are the round keyboard connector, the DB-submineature VGA connector and the printer connector. The power connector is also female.

hp power

You all should be familiar with the HP(stands for Hewlett Packard) type power cable. It is the only type of connector that will fit into a normal personal computer power supply. It carries 120 volts alternating current (120VAC). The three leads carry power, return and ground. With the "rounded" side up, power comes in on the right side lead, return in on the left and ground is in the center. A wall outlet has power on the short slot, return on the longer slot and ground connection is in the U-shaped hole.

Why three leads? Voltage difference only happens when it is relative (or compared) to another voltage. Power is compared to return. Ground connects to the computer chassis and to the chassis of much other of the electric equipment in your house. It keeps your body from finding a voltage difference between, say, your vacuum cleaner and your TV. In addition, if something shorts out to the case of your computer, it shorts to ground, causing current to flow and popping a fuse or breaker, instead applying 120VAC to the chassis. Ever been shocked by an appliance? Its chassis is not grounded.

VGA connectors

VGA monitors can be identified by their connectors. Because of the greater information needed for a VGA monitor, it has more data carrying conductors than a CGA or EGA monitor. A VGA/SVGA D-submineature 15 (D-sub 15)connector has three rows of 5 pins (some pins are not used and may be blanked). However, a monitor connector should not fit any other connector so it is the same size as a CGA/EGA connector. A CGA or EGA cable has a DB-9 connector with two rows(like a mouse jack), one with 4 and the other with 5 pins.

serial mouse

Monochrome monitors were the first used on PC's and their video cards used DB-9 connectors. Then came CGA (color graphics adapter) or RGB (red green blue) monitors that supported eight colors. EGA (enhanced graphics adapter) monitors supported sixteen colors. A history of DB-9 connectors for monitors had been established. VGA (video graphics array) monitors supported more colors and higher resolutions than their predecessors and needed more throughput. The connector on the VGA expansion card was of the same shape but used the fifteen pin DB format standard.

Printer Connectors

The printer cable plugs into a parallel port. It is usually addressed as, "LPT1." It has a male DB-25 connector on one end and a Centronics connector at the other. There is no connector like the Centronics on the computer so a backwards cable is simple to spot.



A bit may be thought of as either a one or a zero, an on and an off or, for our purposes, as voltage or no voltage. Eight bits make up a byte. To transfer a byte across a cable you need to send a combination making up eight on's or off's. Serial ports clock through the eight on/off conditions one at a time over one wire. Parallel ports have eight wires clocking one set of eight on/off conditions per step. You can see that with one step the serial port transmits one eighth of a byte while the parallel port transfers the full byte.


Serial Connectors

Serial connectors are normally either DB-9 or DB-25 connectors. In other words, there are either 9 or 25 pins in the connector. Of course, the extra pins in the DB-25 are never used. This is why you might have to plug a DB-9 to DB-25 adapter into your computer to get a serial mouse to work! Make sure that the genders are right on the adapter. Imagine having a female mouse connector and ordering a DB-25 male to a DB-9 female adapter. The mouse would not connect and you would have to make another trip to the computer store.

Keyboard Connectors

The keyboard connector is simple. It is round and goes into the round hole in the back of your computer. There is a dent in the metal shell so that you can't put it in the wrong direction. Keyboards themselves, however, can be wrong for your computer! There are XT or 84-key keyboards and AT or 101-key types. Some keyboards have a switch on back to change from XT to AT. The two types will not work on the other type of computer.

VGA connectors

The DB-15 joystick connector connects into a game port. There may be no game port on your computer. Game port expansion cards can be added to most computers so that you can use a joystick. Many sound cards also carry a joystick adapter.


Connector contacts may be easily damaged. Some mini-DIN connector mice and keyboards have tiny pins that may break off with heavy use. Also, female mouse connectors that should squeeze inserted male pins, ensuring good contact, lose their spring if moved around too much and either lose contact or have intermittent problems. Always screw down connectors. This keeps the pins stable so they will not flex and break off.


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Updated January 24, 1998, 10:52pm. shawn_h@sprynet.com