If your personal computer is more than 2 or 3 years old, it may be worth replacing it. Or it may not.

Desktop PC manufacturers have introduced several new technologies to try to lure you into pulling out your credit card. What's more, PCs continue to get faster and more capacious, with speedier central processing units (CPUs), more random access memory (RAM), and larger hard drives.

Yesterday's technology isn't necessarily a liability. The old maxim, "If it ain't broke, don't fix it," can apply to newfangled computer technology as well.

Before spending good money to make a major change, look into making smaller changes. Ensuring you have enough free space on your computer's hard drive by deleting programs you never use and reorganizing your files using your computer's defragmenting software can return a pokey PC into its former fast-performing state.

You can also incrementally replace or add individual components, including RAM, an internal or external hard drive, a video card, and a monitor, among others. But if you want to use the latest generation of software, it's typically more cost-effective to replace the entire unit, particularly if more than one component needs upgrading.

The two biggest changes in PCs over the past several years involve the two most important PC technologies: the CPU and the operating system. The CPU is a computer's muscle, while the operating system is its brain.

Many of the new PCs on the market today come with "multicore" CPUs. These pack two (dual-core) or four (quad-core) independent processing cores onto the same chip for faster performance. While one core is doing one task, the other core or cores can do other tasks.

Multicore chips from Intel and AMD work best with programs that are designed to work with them, such as Adobe Photoshop. Although, operating systems such as Windows Vista can divide the work just as well if not just as efficiently.

Vista is the other big change in PCs. Introduced in January 2007, its biggest innovations are tightened security, improved networking, and a new interface.

Microsoft's latest operating system has been criticized, however, for its stiff hardware requirements, its compatibility problems with some software and some hardware peripherals, and its intrusive security features. Its adoption rate has been slower than its predecessor, Windows XP.

Some of Vista's problems were addressed with the release of Service Pack 1 in February and March of 2008. Fewer problems have been reported with Vista on new PCs than with upgrading Vista on old PCs. Major computer makers typically spend thousands of hours on compatibility and stability testing, which can be a good reason for opting not to buy components and to put a system together yourself.

When buying a new PC, you have your choice of CPU as well as RAM, hard drive, graphics card, monitor, case, and software.

For most home and office computer users, even the least expensive offering from major manufacturers (those with the least powerful CPU, least amount of RAM, and smallest hard drive) will typically perform well. If you use your PC extensively for computer games or for editing video, you'll benefit from a powerhouse machine loaded with a quad-core processor, lots of RAM, a huge hard drive, and an ultrafast graphics card.

Most PCs today come with widescreen monitors that have the same 16:9 aspect ratio as widescreen TVs. As well as being better for watching movies, they also make it easier to keep more than one program or file open and to view more columns of a spreadsheet. Sizes typically range from 17" to 24".

If you're cramped for space or prefer a more stylish look, a desktop computer with a small case, such as HP's Slimline series or an all-in-one PC such as Gateway's One, can be a good choice.

PCs from major computer makers may seem to come loaded with software, but much of that software typically includes lighter versions of regular programs that skimp on important features, trial programs that can be used for only a limited time, and programs you simply don't need. Sometimes called "shovelware" (manufacturers shovel them on), most of these programs can be uninstalled. Some may turn out to be useful, though, so it doesn't hurt to try them out.

Many PCs today come standard with the Microsoft Works suite of programs and a trial version of the more extensive Microsoft Office. Works is fine for most home users, though you may find upgrading to Office convenient if you bring work home with you, including presentations.