By Lincoln Spector
November 10, 2009

A number of issues can slow down a once fast PC. Here are some of the most common.

An overloaded and fragmented hard drive. If your drive is too full (more than about 80 percent), or too fragmented (the two often go together), it could be slowing down your PC, especially if you don’t have much RAM.

Defragging is the easiest solution, so you should try that first. To defrag in XP, select Start, then My Computer. Right-click your C: drive and select Properties. Click the Tools tab, then Defragment Now. Vista defrags automatically–or at least it does so in theory. See Vista Defrag Problems for details. Or you can go with a third-party defragger. Forum regular Flashorn recommends the free MyDefrag, which looked pretty good when I checked it out.
If your drive is getting full and defragging doesn’t help, you may have to make hard decisions about what you can delete or off-loaded to an external drive. Or you could replace the drive with a larger one.

Avoid new programs. Software has a way of cancelling out Moore’s Law–as hardware gets faster, software gets slower. (I attended a programming conference once where Bill Gates advised programmers to write for the most powerful PC currently available, because that would match a normal PC when their product was released.) So if you keep buying the latest office suite or photo editor, performance will suffer.

Watch your security software. You can avoid upgrading Office and Photoshop, but you have to keep your security software up to date or you risk infection. Major security suites like Norton and McAfee use a lot of resources, and keep using more with each major upgrade. They can seriously slow down an older PC. Consider switching to smaller, sleeker (and often free) alternatives. See Can You Trust Free Antivirus Software? and What Free Security Programs Can Protect My PC? for product suggestions.
Reduce the autoloaders. Your security programs probably aren’t the only ones that load automatically each time you boot and stay in memory, although they may be the only ones that should. Any number of programs you’ve installed may have inserted a piece of themselves into Windows’ Startup list, and could thus be slowing you down. See Why the Slow Boots? for more information.
You could be infected. See Remove a Virus or Other Malicious Infection for details.
And remember, when it comes to upgrading your hardware, adding RAM is relatively cheap and usually very effective.