Yes all the data has to come in the beginning from permanent storage, but then kept in memory until there is not enough memory left then the "Garbage Collector" (background process), yes it is named that, then removes it. Keeping it around in working memory is MUCH faster and battery saving than have to delete it and then re-retrieve it over and over again. Plus, the UFS 3.0 is much faster and energy efficient than previously as well! So these silly "memory cleaner" apps that kill items in working memory to make more memory available on the Android platform is a silly concept and actually makes things worse! The only time where that helps is if you have a slower processor which is not as busy if there are fewer things in memory - however that is not an issue either with these powerful handheld machines. Those apps also often came from people that were used to using other OS's (such as Windows) that can run faster if there is more memory free...