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Ports and Headers

Ports are connectors used to connect external cables and devices to the motherboard. In addition to the keyboard and PS/2 mouse connectors, some types of motherboards (such as the ATX) have on the back edge of the motherboard integrated serial and parallel ports.

Motherboards that don't use integrated ports, use headers on the motherboard instead. Headers are groups of pins used to connect devices or ports to the motherboard. A cable runs from the port and is plugged into the header on the board. The following are the headers that are commonly found on a typical Baby AT style motherboard (though some of the functions are provided as headers to ATX style boards as well, if an integrated port is not provided):

• Serial Ports: As mentioned, there are usually two serial port headers. Each has 9 or 10 pins (only the first 9 are used, however).
• Parallel Port: This header is used for the external parallel port and has 26 pins (25 are actually used).
• PS/2 Mouse Port: Some good motherboards provide a header for a PS/2 mouse port when this port is not already on the board. This lets you add a PS/2 port yourself so you can enjoy its advantages. The PS/2 mouse header has 5 pins.
• USB (Universal Serial Bus): A new technology, USB is proposed to be the new standard for connecting devices such as keyboards, mice and external modems to the PC. Since it is not in common use yet, many motherboards provide a header for you to run a port for it in the future if needed, instead of an actual port (which will appear on future boards if and when USB catches on). This header has 10 pins.
• IR (Infrared) Port: Some motherboards have a header to allow you to run a connection for an infrared communications port, typically used for wireless communication to printers and similar devices. Infrared ports are far more common on laptop computers than desktop machines. These headers have 4 or 5 pins.
• Primary and Secondary IDE/ATA Hard Disk Interface: Most newer motherboards have integrated headers for two IDE channels. Each has 40 pins.
• Floppy Disk Interface: Most newer motherboards provide a 34-pin header for the floppy disk cable.
• SCSI: Some motherboards have integrated SCSI ports or headers, though they are uncommon. They are either 50 or 68 pins in size, depending on the flavor of SCSI implemented.

Note: Older motherboards that don't have integrated serial, parallel, floppy disk and IDE hard disk headers or ports use an I/O controller board that plugs into an expansion slot, to provide these functions. The connections are almost identical, although in some cases additional jumpers have to be set. Consult the manual for the I/O controller board for details.

Next: Pin Connectors

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