The 2GB in his screenshot means that 2GB has been malloc'd and used. RAM reported as in use by an application is not being used by the OS to cache things.
RAM that's reported as "free" by OS X's activity monitor/windows' task manager is used for disk caching.
RAM reported as in use by an application is in use by that application. It could be using some sort of internal cache, but it does not give that memory up to other apps under memory pressure except by the OS swapping it out which gets very slow.
RAM that's reported as "free" by OS X's activity monitor/windows' task manager is used for disk caching.
RAM reported as in use by an application is in use by that application. It could be using some sort of internal cache, but it does not give that memory up to other apps under memory pressure except by the OS swapping it out which gets very slow.