Windows Disk Protection (WDP)
WDP is a cool technology which caches changes made to any files on the Windows system partition. The cache is a physical file (C:Cache.WDP) which by default will take up 50% of your system partition (or up to 40 GB as a maximum), but this can be tweaked to a minimum of 2 GB by clicking “Change cache file size” in the “Protect the Hard Disk” window. The cache is cleared at certain intervals - my recommendation is with every restart (during the boot process). Tweaking the cache file size could require more reboots.
Compared to Windows System Restore (WSR) it is much more effective, as WSR only monitors changes to a core set of system and program files (like the important registry files). But on top of that WSS, with WDP enabled, will even restore the condition of personal user profiles and data (ex. Desktop, Favorites, History, Documents, etc.). This is done automatically without any user or admin intervention!
What is important to understand about this is how Schedule Software Updates works with WDP enabled. Basically, this is the update procedure in a nutshell:

• Active users are logged off when the scheduled update time has arrived.
• The computer is restarted so any disk changes are cleaned.
• Shared user accounts are disabled to prevent unapproved disk changes.
• WDP: “Retain all changes permanently” is enabled automatically to make sure changes are saved.
• Updates are downloaded and installed (manual scripts are executed).
• The computer is restarted.
• WDP is set back to “Remove all changes at restart”.

With some scripting skills you can make sure your system is nice and clean – and automatically brought up to date at the same time. This is the main difference between WDP and hardware protection solutions.