Reader John Coggins recently emailed me wondering whether it was time to upgrade his seven-year-old PC, even though it's working fine. That got me thinking about this post. All things considered... when should you upgrade your computer? Here are some rules of thumb to keep in mind.

• Dead Components - Eventually your hard drive, optical drive, power supply, or motherboard will fail. These events can range from minor annoyances to catastrophic disasters, but depending on the age of the computer, any of them could be cause for upgrading to a new machine. Consider the power supply. Old, cheap power supplies are frequent failure points, and new supplies often don't fit in old cases and/or don't have the right connectors to work with old motherboards. You can hunt down compatible equipment and adapter cables, but even then it can be dicey installing it. Last time I upgraded an ancient computer's power supply I had to drill new holes in the case to line up the mounting screws properly. At some point, you might just say it's not worth the trouble and that it's time to dump the old PC and get a new one. On the other hand, motherboard meltdowns are usually so severe and expensive to repair that a new PC is in order right away.
• New Software - Whether you should upgrade to Vista is a wholly separate discussion, but if you really want to run it, you're not going to be doing so on seven year-old hardware. When a new OS rolls around, you'll usually find online advisors that can evaluate whether your old PC is up to the task or whether you need an upgrade. You'll find the Vista Upgrade Advisor here. This is also good to think about if you are upgrading a major piece of software that you frequently use. If you find it runs very slowly on your old PC, it may be time for a new one (or at least some more RAM).
• Valuing Your Time - Even with RAM upgrades and other internal tweaks, there's only so far you can upgrade any PC before maxing out its capabilities. And over time it will run slower and slower, especially as software (see above) gets larger and larger. If you find yourself launching applications, then wandering off to do something else while they finish loading, it's probably time for a new computer.
• Compatibility - Newish features like Firewire and USB aren't available on old PCs. Not a problem if your parallel port printer is still running, but what happens when it croaks? You might need a new PC just to be compatible with peripherals you need (though add-in cards can be a stopgap measure). Ditto for software: An old operating system like Windows 98 or 2000 won't run most newly released titles.
• Gaming - This almost goes without saying, but most gamers upgrade to new hardware every one or two years, simply to keep up with the extreme demands that the latest games place on their computers.

The bottom line: If you are using your PC for basic needs and it is serving you well, there is no reason to upgrade it just because it's getting old, unless you simply want to see what you're missing. With regular maintenance (particularly dusting inside the case), it should survive for a long while: 10, 15, even 20 years is not unheard of, though their utility dramatically diminishes after 10 years. That said, your risk of hardware failure increases as time wears on, as moving parts wear down and solder starts to become brittle and loose. Make sure your backups are up to date, no matter how young your computer might be.