System ROM space available?

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http://forum.xda-developers.com – Hi - probably a stupid question, but when I open up Titanium Backup... on the home page, it shows the space available for the various partitions: System ROM, Internal, SD Card, and Ext SD Card. I notice that my System ROM partition is 87% full (87MB free, out of 667MB total). When I first noticed this, I started to move some more apps to SD card, hoping to clear up some space. I think I moved about 15 apps, some of which were pretty large (Angry Birds, Angry Birds Rio, Firefox, for example). Yet, after a reboot, the System ROM space availability was exactly the same. What gives? Is this (HowTos)