Registry keys are files responsible for saving configuration settings and similar information in a database called the Windows registry. A registry key can be added, edited, or deleted by the operator and various programs. For example, a newly installed program might ask for an activation number and then create and store this information in the Windows registry once inputted. Every time the program is opened, it might check the activation number on the registry key to confirm that the user paid for the program and eventually delete the key when the user uninstalls the program. This information is an essential part of a Windows operating system (OS), which is the only OS that stores information in this way.
The Windows registry is arranged in an hierarchy, with sometimes only certain parts of it available to specific programs, users, or remote systems. Basically, this means Windows can prevent a program from accessing a registry key that is especially important or even prevent it from adding and editing registry keys altogether. The exact location of a Windows registry depends on the OS version; for example, the latest version of Windows might store keys in a different location than Windows Vista or XP.
It is possible to manually edit a registry key, but doing so can cause programs or aspects of Windows not to function properly or at all. Therefore, it is generally recommended to create a backup before deleting, adding, or otherwise manipulating a registry key. In fact, there are programs specifically designed to back up registry keys and reinstall them if something goes wrong with the edit.
The actual benefits of removing unnecessary registry keys is highly debated. Registry cleaners are utility programs used to remove unnecessary registry keys without having the user manually search for and delete them, but they are a source of much controversy. They are often advertised as a way to speed up a computer. Supposedly, by removing useless files, the computer will be able to pull information more quickly. A registry key normally takes up an insignificant amount of space, however, and removing the wrong registry key can result in the computer crashing or no longer starting up. On top of that, malware and scam software frequently mimic registry cleaner programs in order to cause harm to the computer or trick the user into purchasing the bogus software one or more times.
Some criticisms of the registry key system revolve around the idea that it may complicate certain tasks unnecessarily, duplicate other functionality, and otherwise be difficult to interact with. It can be difficult to interact with individual registry keys, as they are not easily readable, so it can be hard to troubleshoot problems. Sometimes it is also asserted that the registry system makes it more difficult to fully do things such as remove applications from a computer system, because the task may have to be carried out separately both on the file system and the registry system.