A registry cleaner is a type of software utility designed for the Microsoft Windows operating system whose purpose is to remove redundant or unwanted items from the Windows registry. The necessity and usefulness of registry cleaners is a controversial topic, with experts not agreeing on their benefit. Registry cleaners, or registry cleanup software, can improve the performance of computers by ridding the registry of redundant information. On any computer running Microsoft Windows, the Windows Registry acts as a sort of DNA. The registry is essentially a database containing basic guidelines, settings, and other information that tell your PC and the programs it runs how to behave, both on an individual level, and in relation to one another. Each time you use your computer, the applications are constantly referring to this database of registry files to determine how to function. The Windows Registry is organized into registry hives, registry keys and sub keys, and registry values. The values are the actual settings that dictate the behavior of your hardware and software. The keys are the files where these values are stored (and sub keys are then sub files). Registry hives are groups of keys that are stored together in a major section of the Windows Registry. When the registry keys or files become corrupted, you will experience irregular and probably difficult behavior of your computer. You may find that certain windows will not close from the desktop. Corruption of the registry files does not necessarily mean corruption in the sense of acquiring a virus. It simply means that the registry files have been disturbed. Most commonly, this happens during the shutdown process of your computer. For example, if your computer is shut down improperly (such as an immediate and unexpected shutdown due to power failure), this may interrupt communication between a program or setting and the registry keys. The shut down leaves that communication incomplete, which can result in an improperly functioning registry value upon start up. However, the cause of your corrupted registry files may also be found in faulty hardware within your computer, in which case the hardware company will need to inspect the equipment directly. To correct this problem, you will typically need to repair registry files that have been corrupted in order to turn around the corrupt registry and restore your PC to normal operation. One of the best (and easiest) ways to do this is through the use of a Microsoft Registry Cleaner tool, which can do most of the steps necessary for you, while still leaving options for you to undo the changes to the registry after the fact. However, if you would like to fix the registry errors manually, this can be done as well. But keep in mind that unless you are confident in your computer skills and know what you are looking, you should not attempt to alter the registry, as you could cause many other complications throughout the computers performance. To repair corrupt registry files, it is first important that you provide yourself with several forms of safety net. Before you begin, set a system restore point so that if something goes wrong, you can back up Windows XP or Windows Vista to a point in time before you altered the Windows Registry. Also make a back up copy of the whole Windows Registry. This means saving all your registry hives on an external device (CD, thumb drive, external hard drive, etc), or by saving a copy under another name on your PC.