Installing recent socketed processors—the Intel Pentium III/4/Celeron or the AMD Athlon/Duron—requires essentially the same steps described in another article i wrote, except that recent processors do not require the motherboard be configured manually.

Most Socket 370, Socket 423, Socket 478, and Socket A motherboards are self-configuring. They detect the type and speed of processor installed and properly configure FSB speed, CPU multiplier, voltage, and other settings automatically. However, some motherboards intended for overclockers allow overriding information supplied by the processor—for example, by setting a 66 MHz FSB Celeron to run at 100 MHz FSB. Depending on the motherboard, changing such settings may require setting jumpers or altering the default BIOS settings. All such motherboards we have seen default to "Auto," which uses the settings supplied by the processor.

There are, however, several issues to be aware of when installing a modern socketed processor

Compatibility

Compatibility between motherboard and processor is a major issue. That a processor physically fits the motherboard socket is no guarantee that it will work at all, or even that attempting to use it will not damage the processor and/or motherboard.

With Socket A, AMD has done a much better job of maintaining forward- and backward-compatibility than Intel has done with Socket 370. Even so, with either AMD or Intel processors, it's important to check that the motherboard supports the exact processor you plan to install.

In particular, make sure that the motherboard is rated for processors at least as fast as the processor you plan to install. If the motherboard documentation mentions only slower processors, don't give up hope. High-quality motherboards are often over engineered, using larger VRMs than necessary to support the processors they were designed for. It's quite possible that the motherboard maker issued updated specifications for your motherboard that include support for faster processors. Check the motherboard manufacturer's web site to make sure.

Also verify that the motherboard supports the FSB speed of the processor. If it doesn't, the processor will still operate, but at a much reduced speed. For example, installing a 133 MHz FSB Pentium III/933 in a motherboard that supports only a 100 MHz FSB causes that processor to run at only 700 MHz. Similarly, installing a 266 MHz FSB Athlon in a motherboard that supports only the 200 MHz FSB means that processor runs at only 75% of its rated speed.

BIOS revision level

The BIOS revision level can determine which processors your motherboard supports. A later BIOS may add support for faster versions of a given processor, and may also add support for an entirely new processor. For example, we have an early Slot 1 board that was designed for the cacheless Slot 1 Celeron and did not support later Slot 1 Celerons, which included embedded L2 cache. A BIOS update for that board added support for cached Celerons, and a subsequent BIOS update added support for the new features and changed caching scheme of the Pentium III. Don't assume that because you just purchased a motherboard that it necessarily has the latest BIOS. Some makers, notably Intel, issue BIOS revisions very frequently, and the motherboard you receive may have been in the pipeline for weeks or even months. Before you install a processor in any motherboard, new or old, the first thing you should do is identify the motherboard precisely, check the manufacturer's web site for the most recent BIOS update, and download that update. Once you have the system up and running, install the updated BIOS before you do anything else.

A motherboard with an early BIOS revision may create a "can't get there from here" situation. That is, the processor you want to install may refuse to boot without a later BIOS revision than is currently installed on the motherboard. In that case, the best alternative is to install temporarily a processor that the earlier BIOS supports. That's why when we upgrade older systems, we install the latest BIOS version on the old system before we remove the original processor. That's also why we keep a stack of old processors around.

Chipset revision level

Many motherboard manufacturers, including top-notch ones such as Intel, have a nasty habit of slipstreaming revisions. Even two motherboards with identical model numbers may be significantly different. In some cases, that difference is as trivial as different BIOS versions, which is easily fixed. Other times, though, there are very real hardware differences between the boards, and those differences may determine which processors a particular board supports. For example, Intel has produced the popular D815EEA2 "Easton 2" motherboard in two distinct forms. Both versions use the 815E chipset, but the version with an early chipset revision level does not support Tualatin-core Pentium III and Celeron processors. If you have the earlier version, you're out of luck. The newer processors simply won't run in it.

If you're buying a new motherboard, check the manufacturer's web site to determine the current rev level and ask the vendor whether the motherboard he wants to sell you is the latest rev level. If not, buy your motherboard elsewhere. If you're using an older motherboard, check the manufacturer's web site to determine what variants exist and what implication those variants have for processor support.

Heatsink compatibility

Socket 370 processors are a particular problem in this respect. There are three different physical forms of Socket 370 processors you are likely to encounter. Early Socket 370 processors use PPGA packaging. These processors have a flat top, with the processor chip itself on the bottom (pin) side of the package. Pentium III and Celeron FC-PGA processors also have a flat top, but with the processor chip protruding above the surface of the processor, on the side opposite the pins, where it comes into direct contact with the heatsink. The most recent Pentium III and Celeron processors use FC-PGA2 packaging, which is similar to FC-PGA but includes a flat metal integrated heat spreader that shrouds the processor chip itself.

Each of these styles requires a physically different heatsink. Using an incorrect heatsink may damage the processor, either physically or by allowing it to overheat. For example, clamping a PPGA heatsink (which has a flat contact surface) onto an FC-PGA processor (which has a raised processor chip) may literally crush the processor. Conversely, installing an FC-PGA heatsink on a PPGA processor may allow the processor to overheat because a portion of it is not in contact with the heatsink.

Heatsink rating is another issue. Faster processors generate more heat, and require larger or more efficient heatsinks. Don't assume that just because a heatsink is designed to be used with a particular type of processor it is usable with that processor running at any arbitrary speed. For example, a particular heatsink may be designed to cool an AMD Duron running at 850 MHz or less. Using that heatsink on a 1.2 GHz Duron will likely allow the processor to overheat and perhaps damage itself.

Don't assume that all heatsink/fan units will necessarily fit your motherboard and case. Some heatsink/fan units are physically quite large and may not fit. In particular, the portion of the heatsink that overhangs the processor may come into contact with capacitors and other components that protrude above the motherboard. It's not uncommon to find that clamping the heatsink/fan unit into place crushes components that immediately surround the processor socket, so be very careful. Some case/motherboard combinations are also incompatible with some heatsink/fan units because the heatsink/fan is so tall that it cannot be installed because the power supply or portions of the chassis block the space needed by the heatsink fan. If in doubt, measure the available clearances before you order a heatsink/fan unit, and make sure you can return a unit that is incompatible with your motherboard and/or case.

Whichever processor you install, make absolutely certain that the heatsink you plan to use both fits that processor properly and is rated for the processor speed. If you buy a retail-boxed processor, it will come with a heatsink/fan unit appropriate for the processor. If you buy an OEM processor or are reinstalling a processor pulled from another system, make sure the heatsink you use is rated for that particular processor.

Power supply compatibility

Most people don't think about the power supply when they're building or upgrading a system, but the power supply can be a critical issue. Many systems, particularly mass-market systems and consumer-grade systems from major OEMs such as Gateway and Dell, have power supplies that are marginal at best, both in terms of quality and output rating. For example, we have a full-tower Gateway system that arrived with a 150W power supply, and that's after we paid for an upgraded power supply. How small must the standard power supply have been?

Modern fast processors have high current draws, and you cannot safely assume that the existing power supply has enough reserve capacity to power them adequately. If you're building a system or upgrading the processor speed significantly in an existing system, make sure that your power supply is up to the job. Otherwise, you may find that the system will not even boot. If the power supply is barely adequate, you may find that the system crashes frequently. We often hear from people who've upgraded their systems with first-rate motherboards and processors, only to find that the new system crashes at the drop of a hat. When that happens, it usually turns out that they've used generic memory or that they just assumed the original power supply would be good enough. Often, it wasn't.