Registry Cleaners remove items from the Windows Registry which are no longer in use or are unwanted on the system. Such items may include information left by software that has otherwise been removed from the computer, information that is no longer of use, or keys necessary to the operation of malware. It is possible that these persistent items may interfere with performance or have other negative impacts. The registry cleaner scans the registry, and picks out the unnecessary and/or damaged pieces and deletes/repairs them.
Registry cleaners, or registry cleanup software, can in some cases improve the performance of computers by ridding the registry of redundant information.
Due to the sheer size and complexity of the registry database, manually cleaning up debris and invalid entries would be impractical, so registry cleaners are essentially tools that automate the process of looking for invalid entries, missing file references or broken links within the registry and resolving them.
In certain cases the correction of a invalid registry key can provide significant benefit. For example, a registry entry indicating a program should be run at startup from a network path that no longer exists can delay startup by as long as the network protocol takes to timeout, often a full minute. Most registry cleaners however make no distinction as to the severity of the errors, and many that do erroneously categorize errors as "critical" with little basis to support it.
Noted Windows architecture expert Mark Russinovich has concluded that registry cleaners will continue to have a role until most applications have moved to the .NET Framework platform that does not rely on the registry for application settings.
In 2006 Microsoft introduced a registry cleaner feature as part of its OneCare tuneup process, which may just be a proof of the importance of Registry Cleaner for Windows.
Some registry cleaners offer backup and restore functions that allow the user to revert changes made by the registry cleaner in case they are undesired. A Registry Cleaner may be useful for someone that adds or removes programs from their computer very often, however most organisations would rebuild a problem machine back to a known, good state rather than waste resources trying to repair a machine that is not working. Furthermore, professionals typically use virtual machines for scenarios such as testing or application packaging where programs need to be installed and uninstalled frequently.