content: If you mean trying to install a patch meant for Windows 10 onto Windows 7: Absolutely nothing. The Windows Installer would refuse to run it. Even if you could somehow "trick" it into doing so, Windows' file protection might just revert the changes, since those files were not meant for your OS. Not sure if it goes by just digital signature, or if it checks file versions. (All Win 10 OS files would have a different version in their metadata. If you tried to modify the version metadata, file protection would certainly erase them, because you'd break the digital signature in the process) If you mean running the Windows 10 update installation on a Win 7 machine, then all it does is shove Win7 off to the side into a backup folder (So you can restore back to Win7, or so that the installer can revert back to your original configuration if something gets fucked up in the middle of the install), install Win10, then move your settings over.