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The Xbox 360 hard drive has 4 separate partitions: game cache/updates, system, xbox compatibility, and finally the one you actually store things to. This should help to explain why a formatted 20GB HDD only has ~ 18GB free. You can only directly modify the last partition, but today I learned a way to "clean up" the first partition. Why is this useful? Well beyond the obvious nerd satisfaction of having a clean partition, if a game update gets botched you can use the following key combination to start over, saving a call to support. It's also been reported to fix random freezes that may happen when loading games. If you're an achievement whore such as myself, you can use it to remove any updates that make getting the points more difficult. To perform the maintenance, highlight your hard drive under "Memory" in "System Settings." Then just press

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and confirm you want to wipe out your game cache (does NOT affect your savegames/content). It effectively wipes the partition clean, which means the next time you start a game it will more than likely prompt you to update (unless it's a game the developer didn't care enough to provide updates). I'm on the hunt for more hidden key combos now that I know they exist, it's like discovering the infamous
Konami code in Contra all over again.