'Free' memory is memory not being used for anything of any use. Having loads of free memory is only good in case it has to be used. I don't think the BB starts trashing messages until the free memory is close to zero and the BB needs more.
But almost everything you do (installing apps, running apps, saved emails, maps cached from applications like Google Maps and browser caches) all eat into the available free memory. With some apps it's possible to force them free up memory by deleting the caches they build up (like Google maps, and the BB browser). Having the free memory fall to a few MB is ok in itself - the key is understanding if anything is then going to need more than is available.
Also note that memory no longer needed by an application or the OS isn't freed and doesn't show in the free memory count until the OS performs what's called "garbage collection" (GC). You can't control when GC takes place, and if the OS doesn't NEED to find more free memory, it may wait hours before doing it in background. This is by design and the way memory management works in the BB.
Bottom line is don't worry too much. Look at *average* free memory. Look for that average falling all the time AND tending to towards zero (that may indicate a "memory leak" bug in the OS or an application you're running). Otherwise expect it to fall after a reboot as your apps cache more data, and more slowly as you store more emails and other stuff.
Rebooting normally purges all the cached data, but it's pointless rebooting just for that reason (and to show the free memory before any caching takes place) as all those apps start caching all over again as soon as you use them! Rebooting helps restore function if there's a bug somewhere that ulimately screws things up enough to affect your BB's operation.
Last edited by wibbly : 11-26-2008 at 08:39 AM.