Tom, Shadowstorage is used to store the system restore points (shadows - about 1GB a piece). It is about 15% of your total OS disk/partition but can be activated for any disk/partition. The day your system goes on the blink or shows funny behavior, you can set back to an earlier restore point from when the system was OK. A very useful function. Many people reduce the shadowstorage because of it's size. But I do not necessarily recommend that if you can afford the storage. You deprive yourself of restore options. And there is a lot more to it, e.g. you can also recover defunct or lost files and folders from there (if you like to know how to: http://www.howtogeek.com/howto.....ment-38966). If you need more info, let me know.