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Whether it's to install a new graphics card, add RAM, upgrade your hard drive, or slap in a new power supply, sooner or later you'll open your PC's case and plug something into your motherboard. If you haven't looked inside a PC in the last year or two, you may not recognize everything there. For starters, most new motherboards include PCI Express x16 and other new connectors. Here's a tour of today's motherboard.

CPU: A processor rarely needs replacing, and CPU upgrades are seldom cost-effective. But because new CPUs run hotter than their predecessors, you'll find more heat-sink fins within the PC's case. It's crucial to periodically blow out the dust that impedes their efficiency. If you want to beef up your PC with a faster CPU, you may need to upgrade the CPU cooling fan as well. An extra hard drive, a high-end graphics card, or an overclocked CPU can also cause your system to overheat. For more on keeping your computer cool, click here to read my February 2002 column, "A Cool Breeze Keeps Your PC's Innards From Frying."

RAM: Adding memory to your PC is often the simplest and least expensive way to give it more oomph. But RAM types are always changing--DDR2 is the latest and fastest flavor. In fact, the trickiest part of a RAM upgrade is finding the right type and capacity of RAM modules for your PC. Click here for Stan Miastkowski's step-by-step instructions on installing RAM. And to keep an eye on your available memory, click here to download the no-cost FreeMem utility (see FIGURE 1).

PCI Express slots: Many high-end PCs now have PCI Express (PCIe) expansion slots in addition to standard PCI slots, which have been around for years. PCIe slots provide up to 30 times the throughput of the PCI bus and will eventually replace both PCI and AGP slots. Fortunately, your old PCI sound, network, and other expansion cards won't be orphans for a while; today's transitional motherboards have both PCI and PCIe slots.

You may not be able to use your current AGP graphics card in your next PC, however. Most new PCIe motherboards sold in this country use a PCIe x16 slot, rather than an AGP slot, for graphics cards. Systems supporting AGP 8X and PCIe x16 may be in the pipeline, though: Chipmaker Uli has announced a new chip set that supports both AGP 8X and PCIe x16.

PCIe slots come in different lengths, corresponding to the amount of data they can move. PCIe x1 slots replace the standard PCI port and are about 1 inch (or 26mm) long. They move data on and off the motherboard at up to 250 MBps in each direction at once. The PCIe x16 slot that replaces the AGP graphics-card slot is 90mm (about 3.5 inches) long, just like a PCI slot. A PCIe x16 slot can move data--you guessed it--up to 16 times faster than an x1 slot can: as fast as 4 GBps in each direction simultaneously.

SATA bus: Serial ATA (SATA) replaces the slower parallel ATA (also called PATA or EIDE) that manufacturers long used to link hard drives and optical drives to the motherboard. SATA ports first appeared on motherboards more than two years ago; many SATA motherboards have PATA connectors as well.

SATA connectors are smaller than their PATA counterparts and support only one drive at a time--so you don't have to fuss with jumpers to set a drive to master or slave as you might with PATA. The thinner SATA cable doesn't clutter the inside of a PC case as thicker PATA cables do; most important, the smaller cable reduces the chance of overheating (the wider PATA cables can restrict airflow in the case). SATA connections are easy to extend outside the PC case to accommodate external hard drives and optical drives.

SATA drives require a special power connector in place of the standard 5V connector used for IDE drives. Many new PCs come with a SATA power connector, but older machines typically don't. You can purchase an inexpensive ($5 to $10) adapter for converting a 5V connector to SATA at your local electronics store.

Light and Sound

DVI port (not shown): Most new monitors and graphics cards are fitted with Digital Video Interface ports instead of the VGA connectors used by analog CRT monitors. DVI delivers digital video but no sound.

HDMI port (not shown): Some high-end PCs have a High Definition Multimedia Interface port, which seems likely to succeed DVI. The slimmed-down, USB-like HDMI connector is easier to handle than a DVI connector, and it delivers both digital video and digital audio--a welcome simplification for home entertainment systems. Note: HDMI also uses the HDCP copy-protection scheme that enables content providers to control the number of times customers can copy HDTV and other high-definition content.

To connect a PC or graphics card that has a DVI port to a monitor that has an HDMI port (or vice versa), use an adapter such as the High Performance HDMI to DVI Video Adapter ($30) available from Monster Cable.

S/PDIF port (not shown): Ultimately, every digital audio signal must be converted to analog in order to drive the flexible diaphragm in a speaker that generates the sound. On many PCs, the sound card converts digital audio to analog signals, which are then sent to the speakers. Digital speakers--such as those using USB connections--perform the digital-to-analog conversion within the speaker.

The longer an audio signal remains digital, the better the sound quality is. That's why many high-end and some midrange PCs now come with a Sony/Philips Digital Interface Format (S/PDIF) port that carries the digital signal directly from the motherboard to the speakers (with no sound card or external device intervening). Look for a small square connector--called a TOSlink connector--on the back of your PC or sound card.

Send your tips and questions to kirk_steers@pcworld.com. We pay $50 for published items. Kirk Steers is a PC World contributing editor.