The Windows registry is a huge database storing thousands of entries, the so called key-value pairs, which are necessary for running your PC's operating system, hardware drivers and other installed software. You can think about it as a central place on your hard drive where crucial information about the different software settings is collected to easily retrieve this data later on.

Such a registry database may contain several megabytes of data, depending on how many programs are installed on a computer. And this database is growing in size with each new software installed on your system, making your registry more and more bloated and fragmented. For the operating system it gets harder to find a certain registry key within such a crowded place, more and more system resources are used just for retrieving the right data. In the end your PC is beginning to run much slower and sometimes you even face complete system freezes.

Registry cleaners are supposed to fix a fragmented and overly sized registry by removing unused entries and storing all necessary ones in an ordered format which the operating system can parse much faster. In order to determine if registry cleaners are really capable of improving your system's speed and stability, you should think about the shear size of such a database. A registry cleaner can scan and fix a registry within seconds, whereas doing it manually would take you several hours or even days, with the risk of accidentally deleting the wrong entries and messing up the whole system. A registry cleaner finds unused entries and removes them instantly while also backing up your original data in case something goes terribly wrong.

My personal tests and those from many people using Windows registry cleaners also show that a registry repair is really improving a computer system's speed. Especially a system that is riddled with dozens of programs and drivers can greatly benefit from a registry optimizer, sometimes the system is running up to 25% faster after such a repair.

But you should also note that a registry cleaner does only make sense in case your system is heavily loaded with data such as programs, drivers, different user profiles and settings. A rarely fragmented and small registry database usually doesn't interfere with your operating system.