DISE: "Drive Image Special Edition backup partition"
It's used to create a backup image your working hard drive. When you use it, it will restore your computer to its factory settings, or point in time you created a backup. It sounds like you've never created a back up, so that's not available to you.
I have no clue how to activate it, but if you do, it will wipe your entire hard drive, and mount the factory image.