Are there any articles or tests published comparing the amount of RAM used by various versions of the OS? For example Mavericks vs Yosemite vs El Capitan? Obviously this question only refers to a system without any apps running. In other words, which OS leaves the most available for user apps. Some Macs have only 4GB hardwired, so this question is interesting as it shows the headroom available before starting to page the data. Thanks if anyone can point to an actual study with data, vs anecdotes.