Sockets are female connectors -- holes

Plugs are male connectors -- pins sticking out.

Styles of plugs and sockets

DIN-5 and Mini DIN-6 sockets (holes).

Keyboard. sockets on the box, wired directly from the motherboard, most often located toward the power supply end. The smaller came in use since the PS/2 designs by IBM. There are converters available in case your keyboard plug doesn't fit what you have on your back as a socket.

Bus mice use the same type of mini-DIN socket.

DB 25 and DB 9 plugs (pins out).

Seriel Port. Often called "com" ports. The DB9 does exactly what the DB25 does, and you can get converters from one to the other. Only 7 pins are used on either plug.

At times found on the motherboard, these ports will also show up on I/O expansion cards, and Hard Drive Controllers (where they are often added as a sales "extra").

These are used for: modems, scanners, serial printers, mouse, graphics boards, null modems...

These ports are controlled by a URT chip. There may be a great deal of variance on how well any of these work for different applications, although, for example, a mouse wouldn't care much.

A modem, on the other hand, would want a "better" URT chip. If you nose around on the I/O board, or the HDC board, you may be able to find the URT chip. There are some five models in use.

• marked 8250, 8250A, and 8250B -- the oldest versions, limited in speed, and with a few bugs, which at times do not matter. You can run null modems and mice from these, but don't use them for high speed external modems.

• marked 16450, and the buggy 16550 -- used in AT class of machines. OK for all practical purposes, except external modems. You may find these on some I/O boards.

• marked 16550A -- This version corrected all the bugs in previous editions, and operates faster. It can be used with high speed external modems. Most likely you will have these URTs if your machine is less than 5 years old.

Note that internal modems all use their own 16550A URT chips. No worry.

DB 9 socket (holes).

Monitor. Found on video (graphics) cards, some on PS/2 type of mother boards. The plug is used for MDA, CGA, and EGA monitors, and a very few older VGA monitors. What monitor they will operate with will depend on the board, or on the settings on the board.

Note that that old MDA boards will also operate at composite video, so that Video Monitors with "video-in" (RCA) plugs can be used. There are adapters from the DB 9 plug of the MDA video adapter to an RCA plug (Pins 7 and 1 are used, pin 1 is ground).

Hercules monitors will work with MDA boards, or with Hercules boards. Hercules is B/W (orange on black, or green on black), and will do graphics, although slowly. You may have to set some motherboard jumpers and CMOS settings in order for it to work.

If the Hercules monitor is the only video card, it will be used by the system (although the BIOS may complain during boot-up). If used in conjunction with any other video card (MDA, CGA, EGA, VGA), the Hercules monitor can be used as a scratch pad to post information to while you do graphics work on another monitor.

DB 15 socket (holes) - note that there are three rows of holes.

Monitor. Found on VGA, XVGA, and SVGA video (graphics) cards, some on PS/2 type of mother boards.

DB 15 socket (holes) - note that there are two rows of holes.

Gameport. May be found on video cards, on I/O cards, on HardDrive Controllers. This is a game port, and a joystick plugs into the socket.

DB 25 socket (holes)

Parallel Port. This is a parallel printer port. Often found on video cards as an extra, frequently found on HardDrive Controller cards, and on I/O cards. Often directly on the motherboard.

It may be used for a printer, or an exterior Zip drive, scanner, or other specialty equipment. It is called a "parallel" port because data is sent and received on 8 lines at a time (rather than the serial ports, which only use one line for data out, and one for data in).

At the printer the parallel port cables often use a "Centronics 36" -- a strange looking connector the size of a DB 25 but with two rows of teeth, and wire clips at the left and right. These are being replaced by smaller connector which looks like a sized down DB25, with locking clips on the side.

A gazilion additional connectors..

DB 40 and DB 50: Ancient connections for exterior Floppy Drives or Hard Drives.

Coax connectors for networking along a bus.

RJ-45 telephone like connectors (but wider) for networks on 10BaseT hubs.

DB 15 with a sliding lock: also used on networking cards.

50 pin and 68 pin SCSI connections. These look like DB 25 type connectors, but less wide, and with locks at both ends for the cables.

See also this text file on [pins-out].

How many plugs and sockets

You probably have only one Video socket, but could have up to four serial ports (DB 25 or DB 9) and three parallel ports (DB 25).

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