The Windows registry is a huge database of settings — both for Windows itself and for programs you install. For example, if you install a program, there’s a good chance that program would save its settings to the registry. Windows would also save pointers to that program. For example, if the program were registered as the default program for a certain file type, Windows would save a registry entry so it can remember that’s the default program.

If you uninstalled the program, there’s a good chance it would leave all its registry entries behind. They’d stay in your registry until you reinstalled Windows, refreshed your PC, “cleaned” them with a registry cleaner, or deleted them manually.

The Reality

In reality, registry entries aren’t a drag on your computer’s performance. The registry is a massive database containing thousands of small plain text entries. Even removing a few thousand entries won’t make an appreciable dent in the size of your registry.

There’s no point in running a registry cleaner constantly — many registry cleaner companies recommend running their cleaner once a week. Such problems would be better dealt with by solving them when you encounter them. It’s likely that the average registry cleaner would cause many more problems than it fixes if it were run on a regular basis. And even if it’s completely harmless, it’s a waste of your time.

So what does speed up a computer?

Currently, the following popular tools and methods are common in cleaning up a computer:

• SysInternals Autoruns utility.
• Piriform CCleaner.
• Piriform Defraggler.
• Malwarebytes AntiMalware.
• Uninstall programs.
• Uninstall internet browser toolbars.
• Recreate your user profile.
• Replace bloated antivirus suite for lightweight (free) virus scanner in combination with Windows Firewall.
• Rootkit scanning utility (Kaspersky TDSSKiller,  Avast Anti-Rootkit, GMER and RootRepeal.)
• (Reinstall Windows using original Microsoft Windows media or vendor recovery media).