RAM counting at the SGS GT I9000

Hi all, I searched the forum trying to find an explaination to a newcomer to the android world (previous life - symbian guy) I have SGS GT I9000 running Android 2.2

I read the SGS comes with 512 RAM but when I check the RAM counter in the built in app manager I see only like 305MG are counted for, and out of this I have at the moment about 100 MB free.
I have a few apps installed but not on desktop (like tweeter, facebook)

So my question since I did ont see any new post on this subject since July, Where are the 512 RAM ? If I have only about 100 MB left free is it enough  ? Is it not enough ? Can this be a reason for the lagging of th ephone when opening an App especially noticed stickness while typing, opening an email, forward an email etc. I am using the built in app for my exchange server!

I would appreciate any comment, idea, lesson etc.

Thanks,

Hanani

Thank you so much.

Hanani

hey guys

im in the same boat when it comes to sticky buttons.. it was perfectly fine untill i updated to 2.2 official.. ive never rooted the phone yet, never needed too!

so does anyone know why the sgs is so sticky and laggy now? i do alot of email and have been using the Email app (not the S.email/social hub) ive properly installed 10-15apps max so i have not idea why the lagginess??