My phone is running slow and choppy - so I checked the running apps in RAM. My phone indicates that I have 670 MB consumed and only 171 MB available but if I add up the memory footprint of all the apps that are running, I only calculate about 200 MB used. 670 MB - 200 MB is 470 MB. Where is this additional 470 MB being used? How can I clear it? Rebooting doesn't help.