What exactly do you mean by "disk space"? Is it as DanielBoone assumed the disk column of the task manager?
If yes can you post a screenshot of the task manager window? To do that first click on the Disk column to sort the application by the highest using one and then press the Windows Key + Print Screen Key.
The screenshot is automatically saved under MyPictures/Screenshots on your PC.
A normal PC without doing anything on it should have a disk usage of maybe 10% at most. If your disk usage is higher without having the game on then something else is running on that PC.