What does a program do that require a reboot?

Sometimes after I install a program, a window appears on the screen and tells me, "To complete the installation, restart the system".

Now, I just want to know when开发者_C百科 a program requires a reboot and so my question is:

What kinds of operations does a program do that require a reboot?

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One of the most common reasons is if you need to replace files that are in use (such as, say, what Windows Update does), then you have to tell the system to replace it on the next reboot.

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Generally speaking, it's to replace/modify files that are in use by the system (and locked), so they can be updated on boot, before they are locked again.

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Often when they install special drivers / hooks in Windows itself, like creating a virtual drive with DaemonTools. Either they need to replace files that are in use or a reboot is needed for the program to merge in the OS's inner layers.

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The main reason for a reboot is files that in use that the installer could not replace. You can look at the registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\FileRenameOperations and see which files will be removed or renamed after the reboot.