One cause of many system slowdowns is the Windows Registry, which contains information about all your installed software, your preferences, how Windows should run, and more. Over time, as you install and uninstall software, change your preferences, and so on, the Registry fills with outdated entries, incorrect entries, and entries that conflict with one another. The likely result? Your system slows down and becomes more susceptible to crashing.

Note, however, that the benefits of cleaning the Registry are the focus of much debate. In some cases, Registry edits may help an ailing PC; in others, they may create problems. Before diving in, read "" for some analysis.

If you want to try Registry cleanup, look to , which finds problems and fixes them for you. You can have it do all the cleanup automatically, or tell it which items to clean and which entries to ignore.

The software gives you greater control over Registry cleaning than does CCleaner, but you'll be able to fix only 100 entries with it unless you pay the $30 fee to buy it. If you are confident about making sweeping changes to the Registry, get this program; otherwise, CCleaner will do fine for you.