You can also create another partition for games in addition to the OS / apps and storage. These waste a lot of space on an OS partition and just add to fragmentation in the long run, and increase the times need to defrag. As mentioned already you want the primary OS partition small while leaving overhead as it will store the data at the head of the drive which is the fastest region of the platter. Exactly what size you want the OS partition depends on how much stuff you plan to install. I'd keep it simple and store your movies, music, photos, etc on the storage partition and you'll typically be looking at 20 GB-ish space used for OS / apps, so double that or more should be good.