I know my N800 comes with 256MB of onboard Device Memory (as opposed to RAM, Internal Memory and Removable Memory). But I haven't figured out how exactly it is being used.

The Control Panel / Memory utility / Details says:
Total size: 251.5 MB
In use: 99.3 MB
Available: 152.2 MB

and the Data tab says:
861kB Documents (I cleaned out most of the pre-installed stuff)
15.5 MB Installed applications

I'll admit I'm a Linux noob and that may explain my confusion... but if I'm only using a little over 16 MB of the memory for my Documents and applications, what is the other 80+MB being used for?

Is there a swap file in my Device Memory (not the Internal card)? Or other system files?

And is there anything special about the Device Memory (other than it being built in)? Should I try to keep it as empty as possible for swap file expansion? Should I be installing applications to one of the SD cards instead? And if so, how would I do that?

Thanks!