How do I clear space for my ps3 HDD?

Why do I already have so little HDD space on my PS3 160GB?

• I realize, and need confirming, that the Operating System itself takes up enough to leave me with 149 GB, but, what I don't get, is that I have only played 3 games. Modern Warfare 2, Ferrari Challenge, and PSN Home (with 3 GB reserved, but I deleted PSN Home, so, it is not longer reserved, right?) And I had an update for both MW2 AND Ferrari Challenge, and have downloaded two things, The Modern Warfare 2: Stimulus Map pack, and have STARTED downloading the LittleBigPlanet 2 Demo. Can someone please tell me how I already have 128/149 GB? I would love to know, and, will the memory on my PS3 deplete like this ALL the time? Thank you, I am really enjoying my PS3, but this may be a setback.

• Answer:

  Along with Save Data there is also Game Data which will take up most of the space for games as it includes any DLC and game updates. HDD space won't just deplete on its own. I have lots of Game Data and lots of downloads on my PS3 which is only the 120Gb slim and I still have 30Gb left which I have never seen go down on its own.