why is by backup rom so big 1.8 gig

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http://forum.xda-developers.com – I have pretty much a stock rom with just a few mods done to it. When i go into cwm to do back up it looks like it worked fine. Once the phone boots up and i go into my files it shows the backup folder to be 1.8 gig. This is in the cwm folder under backup. Why so big? Sorry I'm still a noob here. (HowTos)