After you install the motherboard inside your computer’s case, your PC might still be missing one or two very important parts: its brain (the central processing unit, or CPU) and its memory (random access memory, or RAM). When you run a computer program, your computer’s CPU performs the calculations and executes the commands stored in that program.

In tandem, your computer’s RAM acts as a work area for the program: storing, changing, and retrieving data. As an example, if you run an address book program on your computer, your CPU can use the instructions within the program to search for names or print address labels, and your computer’s RAM stores all those names and addresses until you exit the program.

I recommend buying a motherboard with the CPU and RAM modules preinstalled (commonly called a populated motherboard, for some strange socioengineering reason). That way, you don’t need to worry about compatibility problems or installation hassles. (Differences exist in socket types, voltage requirements, and physical measurements in both the Pentium and Athlon lines of CPU chips, so not every motherboard accepts every CPU.)

If your motherboard comes with these chips preinstalled, you can skip most of this article and visit your local miniature golf course for a heady 18 holes. If you need to install your CPU or your memory either before you install your motherboard inside your case or afterward this article will attach itself to you like a suckerfish to the side of an aquarium. Just follow the appropriate steps and then test your chassis.

FYI about CPUs

You can choose from a number of CPU models these days, and you might be able to save a little money while shopping if you’re faced with a decision between manufacturers and speeds (or if you’re scavenging from an older PC). Therefore, review the general characteristics of the current crop of computer cranium components. I take them in order of price and power, starting with the low-end processors.

I mention this question elsewhere in this article, but the question bears repeating: What’s the difference between a 2.4 GHz Pentium 4 CPU and a 2.8 GHz Pentium 4 CPU? No, it’s not a trick question! Because the processors are the same type, it’s the speed, which is expressed in megahertz (MHz) or gigahertz (GHz).

When you’re shopping for the processors that I describe in this section, make sure that you get at least the minimum speed for the type of computer you’re building. (If you’re not sure what that minimum speed or type is, see article 2, or visit my Web site at www.mlcbooks.com for my latest recommendations.) However, you can also follow this simple Mark’s Maxim:

Buy the fastest doggone possible processor you can afford!

Remember, adding plenty of RAM is just as important from a performance angle as buying the fastest CPU you can afford. With only 128MB of RAM, for example, Windows is still going to run slowly, even with a super-fast Pentium Extreme Edition processor. You’ll find more details on how much RAM you should add later in this article.

Celeron and Sempron processors

Celeron and Sempron are two processors designed for the price-conscious consumer. In other words, although you get lots of bang for your buck from these CPUs, they aren’t as advanced and don’t have the extra punch of their more expensive brethren. Don’t get me wrong, though: Either of these two processors is still more than speedy enough to power a typical family PC.

The Intel Celeron: The darling of the low-cost crowd

The Celeron, designed by Intel as a cheaper alternative to the Pentium since the days of the Pentium II, works quite well if you’re building a midrange computer for use with an office suite or if you plan to explore the Internet. The Celeron has a lower amount of cache memory than the Pentium, so it’s not as efficient as the Pentium 4, and its raw megahertz speed rating is typically slower than a full-blown Pentium 4.

Celeron processors are a little faster than the Sempron, which I discuss next. Celeron processors typically handle data at a faster bus speed than Sempron CPUs the faster the bus speed, the faster the CPU can send and receive data to other system components, such as your video card and system RAM.

The AMD Sempron: A bare-bones hot rod

Because AMD designed the Sempron to compete directly with the Celeron, the Sempron is usually neck-and-neck in performance benchmarks. On the downside, because the Sempron is a stripped-down Athlon XP, it typically also runs hotter. I therefore recommend that you pick up a second fan for your case.

Pentium and Athlon processors

In this section, I cover the big CPU twosome dominating the current PC scene. The Pentium Extreme Edition and the Athlon 64 series are suitable for high-end power user systems. Either of these processors is my first recommendation for most folks playing the latest computer games, working with digital video or music, or using demanding business applications.

One step down the performance ladder, the Pentium 4 and the Athlon XP processors are perfect for a midrange PC for home or office. I cover them as well.

Today’s Pentium 4 processors include hyperthreading technology, which allows a single CPU to perform like multiple CPUs. In fact, Windows XP and 2003 Server think that you’re running a dual-processor motherboard! The adage “Two heads are better than one” is just as true when it comes to computer CPUs, and hyperthreading is a feature that you should ask for if you’re buying a new CPU. A PC using one of these chips is more efficient and runs significantly faster when you’re running more than one application at a time.

The Intel Pentium Extreme Edition: High-end horsepower

The Pentium Extreme Edition CPU is a super-fast processor that features Intel’s hyperthreading technology, providing the best performance for today’s games, 3-D applications, and video editing. The latest versions of the Extreme Edition CPU are dual-core processors, so they excel at multitasking and number crunching. At the time of this writing, the motherboard selection for Extreme Edition CPUs is sparse, but the market will continue to expand as time goes by. The Extreme Edition is a socket 478 or LGA 775 processor, depending on the version. (Remember, the type of socket your motherboard has think “connector that the CPU plugs into” determines what type of processor you can use.)

The Intel Pentium 4: Still king of the hill

The Pentium 4 is the most popular CPU on the market, and with good reason: It’s a fantastic all-around CPU. Although it doesn’t operate as efficiently as a standard Athlon 64 CPU and doesn’t offer 64-bit operation the Pentium 4 is often faster in raw speed, and it runs with a wider range of motherboards. It’s a great choice for just about any PC. The Pentium 4 is a socket 478 processor.

The AMD Athlon 64: The tyrannosaurus rex of processors

The Athlon 64 X2 is AMD’s fastest, most efficient, and most advanced CPU. The Athlon 64 CPU X2 even outperforms the Pentium Extreme Edition dualcore processor line, and it’s a particular favorite with the gaming community.

But wait: Before you close this article and head to your Web browser, you should know that the Athlon 64 X2 is not the right choice for everyone. Like a sports car, the Athlon 64 X2 is far more expensive than a standard Athlon 64 processor. Plus, fewer motherboards are approved for use with the Athlon 64 X2. I would recommend it for techno-wizards who want absolutely the best performance available in a CPU or for those folks who want to look forward to three or four years of use before they plan to buy another motherboard or build another PC. AMD’s other 64-bit processor is the Athlon 64 FX series, which delivers a level of performance between a standard single-core Athlon 64 and the Athlon 64 X2. Athlon 64 CPUs are socket 754 or socket 939, depending on the version.

By the way, that 64 in the Athlon 64 designation is no accident: All Athlon 64 processors support the latest 64-bit version of Windows, Windows XP Professional x64 Edition, as well as 64-bit Linux and the upcoming Windows Vista. The dynamic duo of one of these operating systems and any Athlon 64- bit processor results in faster performance, support for up to an unbelievable 128 gigabytes of RAM, and full support for dual-core CPUs. In the Intel corner, Extreme Edition processors with EM64T offer 64-bit support as well.

The AMD Athlon XP: A reliable workhorse

Like the aging Pentium 4, AMD’s Athlon XP is no longer top dog, but it still offers respectable performance for a typical family or office PC, and again it provides more efficient operation than Pentium 4 models with similar speeds. The Athlon XP CPU is a socket A processor.