I recently added RAM to an Exchange 2010 server hopping to free up more memory; but it didn't Upon looking at the task manager I noticed a task called "store.exe" was taking up most all of it. After some searching to find out why here is the answer:
The above link is chock full of great info about why store.exe will consume tons of RAM. I'll sum up:
Store.exe no longer has a database cache limit, it will consume all RAM available minus 2GB approximately. It monitors the system itself and gives memory back to the system as it's needed. It's dynamic. IE: It's normal in Exchange 2007/10 to see store.exe eating up most RAM, it'll give it back if it needs to.
Read the link if you want the big huge in-indepth answer.