Just because your PC feels slow doesn't mean that it is. Any number of things can cause your computer to slow down temporarily: a stuck print job, a badly coded Web page, a hiccup at your ISP, or something else.
Most users have a "gut feeling" about their computer's performance. When booting up takes more than a minute, or apps start to load sluggishly, it's time to put some effort into getting your system into shape again.
But where can you look for quantitative data on which to base these decisions? The best thing you can do is to benchmark your computer to see whether it is really getting slower. PCWorld offers its own benchmark tool, WorldBench, for purchase, though the $249 price tag is steep for an individual user. Cheaper options abound: One good tool is the free version of PCMark Vantage, which will let you run a limited benchmark of your system to check for trouble spots.
The difficult issue is figuring out what to compare your benchmark numbers with. After all, benchmarks in a vacuum are useless. With WorldBench, you can compare your system's score with those of various modern PCs, as reported in this magazine--or you can look for a review of your system (or a similar one) in our online archive. Another option is to upgrade to PCMark Vantage Basic Edition ($7) so you can compare your score with those of other users who've submitted their numbers online.
Finally, you can use Windows' ‘Performance Information and Tools' Control Panel. The information there is rudimentary, but it's better than nothing.
If you see the numbers slip to 15 to 20 percent below what you'd expect, it's probably time to take action.