May 15, 2012, 7:50 AM — If you've ever opened a PC case and stared inside, or looked at a bare motherboard, you may be taken aback by the number and variety of connectors, pins, and slots that exist on a modern PC motherboard. In this guide I'll identify some of the most common (and a few uncommon) connectors on motherboards used in most home PCs. I won't cover server- or workstation-class boards here, just what you might find in a typical midrange or high-end home PC.
For a similar discussion of the ports that you're likely to encounter on the exterior of a PC case, see "Multiple Ports on Your PC: What Do They Do for You?"
Since no single motherboard contains every type of connectors, I've used photos of four different boards to illustrate key examples. In one or two instances, there is some overlap; but for the most part, connectors are mentioned only once. Many of them may exist across different motherboard designs, however.
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Asus P5WDH Deluxe
Let's start with an older motherboard, an Asus P5WDH Deluxe. This motherboard has a few connectors that aren't included on current-generation boards, as wll as some that do are still included, but are more readily visible here.
Audio front panel: This ten-pin connector links to the front-panel headphone and microphone inputs. The particular connector shown is an AC97 connector, which existed prior to multichannel HD audio. It's still in common use today.
Azalia digital audio header: You rarely find this connector, used to tie the motherboard to multichannel digital outputs on the case, on current motherboards.
Serial-port header: This connector isn't physically present on the board shown--you can just see the solder points for it. But this header does appear on a few modern boards. It supports a nine-pin, RS-232 serial port, usually as a bracket that occupies a slot space on the back of the case. A number of RS-232 connections remain in use today, mostly in point-of-sale devices or specialized test instruments. Consumer boards typically don't have them.
FireWire (IEEE 1994a): Once common as a digital camcorder interface, FireWire has largely been supplanted by USB, and the motherboard makers are gradually phasing it out. Some professional audio hardware still uses FireWire, though; you may also occasionally find higher-speed IEEE 1394b headers, but they are even rarer.
USB 2.0 front panel: These connectors are used to link to the front-panel USB ports on PC cases.