Each one uses very little hard drive space, but the operating system still has to filters through all of them, which slows it down a bit. Once you’ve been running the Windows OS for some time - installing and uninstalling programs, and swapping in different keyboard and mice - you end up with hundreds or thousands of registry entries that are completely useless. Changes to the registry by malware require immediate attention.

In particular, malware is regularly designed to change the values of startup keys so it will be activated each time you restart the PC. Many types of malware attack and modify the registry.

If your computer is turned off, crashes or dies without going through the normal shutdown routine, it could cause an issue in the future, but this is unlikely. Each time your computer shuts down, a copy of the registry is saved to system memory. The registry can also fragment when software is uninstalled, upgraded or updated.

Registry cleaner software will state that your programs will be confused by the duplicate entries, slowing your machines performance, but that is not true. Duplicate keys are made when you reinstall, upgrade or update software on your machine, including the operating system. Registry cleaner software will often claim these are an immediate issue, but in reality, they will just use up a few kilobytes of free space on your disk. Orphaned entries occur when you uninstall software and small fragments of registry entries are left behind. Some are worth worrying about, and others are not. There are several common causes of registry errors.

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