Why is my machine slowing down?

If the slowdown is sudden and severe the first thing that comes to mind these days is a virus. Thankfully, assuming your machine is still usable it's easy to check. Grab a virus scanner, make sure the virus definitions are up to date, and scan your machine immediately.

Along those same lines scanning for spyware is a good idea, too. Spyware isn't considered a virus so it typically isn't caught by anti-virus programs. Regardless, some spyware can adversely affect your system performance besides possibly violating your privacy.

I've got some recommendations for anti-malware (virus and spyware) tools here as well.)

Another step I take when my machine seems to be slowing down is to fire up task manager on Windows NT, 2000, or XP, or run SysInternals process explorer on almost any Windows system. These tools can show you if one process is using an inordinate amount of CPU time. If so, you can then investigate why that process is running and what might be causing it to use up so much time.

While we're looking at processes, another good thing to look at is just how many are running and how much memory they're using. It's possible that there are simply too many programs running at once or that one of them is taking an inordinate amount of memory. When the system is running low on memory Windows will use the hard disk for the overflow at the cost of speed. Task manager has a nice view under the "Performance" tab that will show you how much memory is in use, and both taskman and procexp can show you how much memory each process is using. If you're running tight try shutting down some of the processed you don't need. (See this Ask Leo! entry for tips on controlling what gets started automatically, and this entry for some ideas on how to tell just what each process is.)

If your system slowdown has been gradual over several weeks or months it's possible that your hard disk has become fragmented. All recent versions of Windows have defragmenting tools. Under XP, in Windows explorer, right-click on your hard disk drive (normally C:), select Properties, and click on the Tools tab - there you'll find the disk defragmenter. It's a good tool to run periodically though how often will vary depending on your computer usage.

On some systems it's possible that network traffic or "noise" is causing your network adapter to impact your system to weed the actual information you care about. This is particularly true if the machine you are concerned about has internet connection sharing turned on. A quick test is to unplug the machine from the network and see if anything resolves.

It's also quite possible that you've slowly been asking your computer to do more than before. I know I keep coming up with more things including more software, more tasks to perform, and so on. Memory seems to currently be the single most cost effective investment you can make to improve the speed of your machine. Windows loves more memory.

And finally a word about hardware. Most hardware failures tend to be catastrophic - meaning that when something breaks, things don't slow down, they stop entirely. However hardware slowdowns can still happen. A good example might be a hard disk that is beginning to have trouble. Under Windows NT, 2000, and XP, a look in the event log can often be educational. Start -> Run, enter "eventvwr", and then review recent entries in the System event log and the Application event log. Unfortunately even a perfectly healthy system will still have a certain amount of "noise" in the event log. If you can compare current entries with older ones to see if particular components have have recently begun reporting problems.