Ideally, you want your Windows to keep those 4 folders on the C: drive, but they need to be mostly empty. kemical's suggestion of moving large files from those folders to backup folders with similar (but not identical!) names will definitely help. Moving those over to a different logical partition or physical drive, i.e.: D:, E:, F:, etc. These include the 4 folders: Documents, Music, Pictures, and Videos. Not a good idea to move the essential Data Library folders located in C:\Users\Username as mentioned by nmsuk.
