Sometimes it's sensible to upgrade a PC. Other times it's not. Whether it is economically feasible to upgrade a particular PC depends largely on how old the PC is, its existing configuration, and what you expect it to do.

PCs less than a year or two old are usually easy to upgrade. Components are readily available and sell at market prices. Necessary BIOS upgrades and firmware revisions are easy to obtain. PCs more than two or three years old are harder and more expensive to upgrade. Necessary components, particularly memory and BIOS upgrades, may be difficult or impossible to obtain. Even if you can obtain them, they may be unreasonably expensive. Upgrading one item often uncovers a serious bottleneck elsewhere, and so on. In general, restrict older PCs—anything more than a couple of years old—to minor upgrades such as adding memory, replacing a hard disk or optical drive, or perhaps installing a faster processor. Although you can perform significant upgrades on older systems, it seldom makes economic sense to do so. If an older PC requires more than minor upgrades to meet your expected needs for the next year or so, it's probably not a good upgrade candidate.

The reason most people upgrade their PCs is to improve performance. The good news is that there are several relatively inexpensive upgrades that may yield noticeable performance increases. The bad news is that some are easier than others, and performing all of them can easily cost as much as or more than simply buying (or building) a new PC.

Processor

Upgrading the processor improves overall system performance. In general, newer systems are easy to upgrade, and older systems are more difficult (or impossible) to upgrade. Upgrade only within the same generation—for example, a Pentium 4/1.6A to a Pentium 4/2.8, or a Duron/700 to an Athlon/1800+. If you upgrade within the same generation you may have to upgrade your BIOS at the same time (usually a free download), and you may have to buy an adapter (for example, to install a Socket 370 Celeron in an older Slot 1 motherboard). Avoid upgrade kits, which are usually expensive, provide limited performance improvements, and are often plagued with compatibility problems. Replacing the motherboard, processor, and memory usually costs little or no more than purchasing one of these kits, and the results are much better. Cost: $30 to $200 (although you can spend much more). Difficulty: easy to difficult, depending on the system and the processor.

Memory

If your PC does not have at least 64 MB (Windows 95/98/Me), 128 MB (NT/2000/Linux), or 256 MB (XP) of RAM, adding RAM is the most cost-effective upgrade you can make. Additional memory improves overall system performance, sometimes dramatically. Adding memory beyond 96 MB for 95/98/Me, 128 MB for NT/2000/Linux, or 256 MB for XP results in decreasing returns. The downsides are that many older systems do not cache memory above 64 MB (check the motherboard/chipset manual), which means that increasing memory beyond 64 MB can actually decrease performance, and that you may be sinking money into an obsolete form of memory that cannot be migrated later to a new system. Accordingly, we do not recommend upgrading memory in systems that use any memory type older than SDRAM DIMMs. Cost: $25 to $150 (varies with memory size and price). Difficulty: usually easy, although physical access on some older systems is difficult and the correct memory may be hard to find and expensive to buy.

CD-ROM

If you use your CD-ROM drive only for installing software and listening to music, even an original 1X model suffices. But if you use your CD-ROM drive for playing games, accessing large databases, or ripping audio CDs to MP3 format, you'll want a better drive. Recent 32X and faster IDE models are inexpensive and easy to install. However, rather than installing a new CD-ROM drive, consider installing a CD writer and/or a DVD-ROM drive, both of which offer full CD-ROM functionality and adds additional useful capabilities. Cost: $50. Difficulty: easy.

Hard disk

Modern hard disks are huge, fast, and inexpensive. Upgrading the hard disk not only provides additional storage space, but also can dramatically increase performance if you run applications that access the disk frequently. Older systems cannot recognize large hard disks, but you can get around that problem by using a device driver (usually included with the new drive), by installing a BIOS upgrade, or by replacing the embedded IDE interface with an expansion card ($25 to $50) that supports large drives. Cost: $60 to $250. Difficulty: easy, except for problems migrating existing programs and data

Video adapter

Video adapter technology improves almost from month to month. Even so, if you use your system primarily for word processing, email, web browsing, and similar functions, you won't get much benefit from upgrading to a new video adapter. But if you play 3D games and your video card is more than a year or so old, upgrading to a more recent model can provide dramatic performance benefits. Although it seldom makes sense to install the latest, fastest video adapter in an older system, installing a midrange current video card can boost performance at small cost. Cost: $50 to $200. Difficulty: easy to moderate.

Monitor

Although CRT monitors are a mature technology, manufacturing improvements and other factors have resulted in dramatic price reductions on larger models. Not long ago, 15-inch monitors were the norm and 17-inch monitors sold for $750. Nowadays, decent 17-inch monitors cost $150 and 19-inch monitors $250. If you spend a lot of time in front of your PC, buying a larger monitor may be the best upgrade you can make. Also, unlike most upgrades, a good monitor is a long-term asset. You can use it with your current system, your next system, and probably the next system after that. Cost: $150 to $700. Difficulty: easy.

USB 2.0 ports

Most systems and motherboards made before late 2002 support only 12 Mb/s USB 1.1, which is useful only for low- and medium-speed devices such as mice, keyboards, printers, and scanners. USB 2.0 runs at 40 times the speed of USB 1.1, and supports high-speed external devices such as hard drives, tape drives, and optical drives. If you have an older system, you can add USB 2.0 support by installing an inexpensive USB 2.0 PCI adapter. Some models also include IEEE-1394 (FireWire) ports, which are useful for connecting video cameras and similar consumer devices. Cost: $25 to $100. Difficulty: easy.

Power supply

Although it may seem strange to include power supplies in the performance upgrade category, the fact is that many systems have inadequate power supplies, and replacing the original unit with a better unit can improve system performance and stability. Cost: typically $45 to $125. Difficulty: easy.

Another reason to upgrade a PC is to add missing features. Here are some common feature upgrades:

CD writer

A CD writer allows you to burn your own CDs, which can subsequently be read in any recent CD or DVD drive. CD writers are popular for making archival backups and, of course, are used by many people to copy data and audio CDs. Cost: $75 to $150. Difficulty: easy.

DVD-ROM drive or a DVD writer

A DVD drive allows you to watch DVD movies on your PC and to access the increasing number of databases and games supplied on DVD. DVD drives can also read data and audio CDs, so they are a popular replacement for CD-ROM drives. DVD writers are to DVD-ROM drives as CD writers are to CD-ROM drives. In addition to playing back video, audio, or data DVD discs, a DVD writer can write large amounts of data to a removable disc or cartridge that costs $3 to $40. Cost: $50 (DVD-ROM) or $200 to $300 (DVD writer). Difficulty: easy.

Tape drive

The downside of huge, cheap, modern hard disks is that there is no practical way to back them up short of installing a tape drive. Tape drives store huge amounts of data—up to 50 GB or more—on relatively inexpensive tape cartridges. Cost: $200 to $900. Difficulty: easy for IDE, easy to moderate for SCSI.

Sound card and speakers

If you make no serious demands on the audio capabilities of your PC, the inexpensive sound card and speakers that probably came with it are usable. But PC audio hardware and applications are advancing faster than any component except video adapters, and there are a lot of fascinating new applications, including 3D gaming with positional audio, DVD playback, IP telephony, voice-recognition software, and so on. To use any of these new applications, you may need to replace your sound card and perhaps your speakers. Cost: $50 to $400. Difficulty: easy, except for potential conflicts with improperly uninstalled drivers from the original sound card.

Game controller

Years ago, people bemoaned the fact that PC games were inferior to arcade games or dedicated game consoles such as those from Sega, Sony, and others. Dramatic improvements in PC video and audio mean that nowadays the playing field is level. Many excellent games run on PCs, the Sony PlayStation series and Microsoft Xbox notwithstanding. But getting the most from those games requires adding dedicated game controller hardware, such as a joystick, wheel, or paddle. Cost: $10 to $150. Difficulty: easy.

The ultimate upgrade, of course, is to replace the motherboard, which in effect means building an entirely new PC. Before you undertake a motherboard upgrade, consider whether you might not do better to retire your current PC to other duties and buy or build a new system. If you do replace the motherboard, expect to pay $50 to $250 for the motherboard itself, but also plan to spend another $50 to $250 to replace processor, memory, and perhaps other components, depending on how much can be salvaged from the current system. Difficulty: easy to moderate (although it may be time-consuming) if you have some experience working on PCs, moderate to difficult if you don't.