What does slow computer down over time?

What actually slows your PC down are too many poorly written applications that stay resident in memory and waste CPU cycles, having too many badly written low-level applications that hook into Windows, or running more than one antivirus application at a time. And of course, if you've run your PC's hard drive out of space, you can hardly blame Windows for that.

If you aren't getting the picture, the problem is usually the person behind the keyboard that installed too many junk applications in the first place. More gently put, it's often that (very well-meaning) person's gradual easing of their safeguards and cleaning regimens as time goes by.

Stop Installing Junk Applications

Installing software should be thought of like feeding your PC. If you constantly feed your PC garbage apps, it's going to get sick and won't be able to run fast anymore. These poorly written applications clutter your drive with unnecessary DLL files, add always-resident Windows services when they don't need to, bloat up your registry, and add useless icons to your system tray that waste even more memory and CPU cycles. Usually you can get away with using a few terrible applications, but as you continue to install more and more of them, your PC will slow down to a crawl.

Here's a few tips to help you know what applications you should be careful with:

• Apps that function as an Explorer plug-in, because they directly hook into the shell and any problem will make your entire PC slow or in the worst case, crash repeatedly.
• Antivirus applications are notorious for slowing your PC down, and you should never, ever, ever use more than one real-time antivirus application at a time.
• Anything that says it will "Speed Up Your PC" or "Optimize Your RAM" will most likely slow it down, or best case, do nothing at all. Avoid these like the plague.
• Make sure to install official system drivers from the manufacturer website. Drivers have a huge impact on performance, and you want to have stable, updated drivers.
• Registry cleaners are a mixed bag, and really aren't going to speed up your PC in most cases. The biggest problem, however, is that too many of the commercial registry cleaners set themselves to run at startup in the system tray, wasting your memory and CPU cycles.
• You should strongly consider the idea of using portable applications wherever possible, since their self-contained nature means they won't clutter up the rest of your PC with things you don't need.

source: lifehacker