If you use Windows, you know the story: the months pass, and your once-snappy computer becomes sluggish, unstable, or unpredictable.

The natural impulse is to blame Windows itself. The phenomenon is so well known and widespread that some in the industry have even coined a term for it: "Windows rot." The idea is that, for lack of a specific cause, Windows just performs worse the longer you use it.

The fact is, though, a lot of Windows woes are preventable - if you know how. Windows rot is the predictable result of actions that users tend to perform without knowing how it will impact their Windows-based PCs. So what can you do to prevent Windows rot? Here are some solutions.

Do not install too many fonts

Every font you install in Windows uses memory. If you go through a period of being font crazy and stuff your Windows system full of every typeface you can find, you'll soon have hundreds of fonts installed - and a very slow computer.

Too many fonts especially take a toll on Windows startup. Systems with many fonts installed can take up to five minutes or more just to boot up, and their hard disks will continue thrashing as programs are loaded and used. Even a Windows computer with one gigabyte of memory (RAM) can easily become overtaxed when several hundred typefaces are called upon to load each time Windows starts.

You may have a lot of fonts on your Windows computer without your even knowing it. Sometimes choosing a "full installation" of popular office, desktop publishing, or graphics programs can choke your computer by installing dozens of typefaces.

To see how many fonts you have installed, open the Windows Control Panel and double-click the Fonts icon. If you're having concerns about performance and your font list goes on and on, you've found the culprit. Select fonts you know you don't need, right-click, and choose Delete.

To keep fonts from impacting your system's performance, don't install more than 200 - 500 tops. If you need more, consider using a font manager that allows you to install fonts in groups and remove them when you don't need them.

Do not install and uninstall lots of software

It doesn't seem fair, but the truth is the more software you install and uninstall from Windows, the more sluggish your computer will get. That's because too many program leave their traces even after they're removed. Those traces exist in registry entries that aren't removed, program folders that do not get deleted, and even components of installed applications that are intentionally left behind when the programs are uninstalled.

And then there are also inevitably uninstallations that go awry, leaving you with programs that were not successfully removed by the uninstall routine and that can no longer be removed completely because the program's entry no longer exists in the Add/Remove programs section - or doesn't work.

Bottom line: If you want your Windows PC to remain in top shape, be careful about what you install - and use only the programs you need.

Do not install "warez" or pirated software from Internet newsgroups or file sharing services.

Aside from the fact that downloading "warez," pirated software, and copyrighted music for free is illegal, it's also dangerous - a sure way to get you a Windows computer that's plagued with all sorts of spyware, malware, and perhaps viruses that will infect your computer and slow it down.

Although you may find pirated software on the Internet that is identical to what you'd buy in the store, other applications are bound to be vehicles that unscrupulous hackers use to get their nefarious program code onto your PC. Why take that chance?

Avoid shady Web sites

Do you regularly surf the net looking for freebies and great deals? Look at porn or frequent gaming sites? Watch out. Such sites are notorious hangouts for purveyors of adware and spyware. Some of these programs can and will infiltrate your computer when you visit these shady sites, and before you know it, your PC will be moving slower.

If that happens, be sure you use an antispyware tool or run a spyware scanner regularly.

Do not install games you download from the Internet

Gaming sites - especially those that promise lots of free downloads are tremendously popular - and sometimes tremendously dangerous. As with porn sites, some of these gaming venues harbor spyware and malware - software that will infect your system, run in the background without your knowledge, track your usage of the Internet, and bring your system to a crawl.

Be suspicious of freeware and shareware

Most freeware and shareware does not contain spyware or other malicious code. But freeware and shareware applications tend to be produced on a budget - or with no budget at all.

Consequently, testing of applications is sparse or nonexistent, and plenty of free programs are so poorly written that they can negatively impact your PC's performance. So be careful about what you install. Try to read reviews of freeware before you turn your PC over to it.

In general, Henry David Thoreau's golden rule of life - "simplify, simplify" - applies to computer users as much as it does to philosophers. If you can slim reduce what you need on your Windows computer to the bare essentials - and forego the untested and unproven - you'll end up with a computer that works as well on the third year that you have it as well as it did on the third day.