I'm currently looking for a way to backup Windows system. I'd like to know how a program installation updates Windows? When a program installed to Windows, files will be created in which folder? Is it possible that program or malware overwrites initial Windows system files?

Btw, can Windows registry be restored by restoring the files contain the Windows Registry? & is Windows registry control over all the system files? Does this means that if the Windows registry is normal, even though the Windows folder contains malware, the malware won't be executed as well?

Is there any software that can provide solution to my mentioned probs?