I recently switched from a 2014 mid MacBook Pro Retina with 2.7 GHz and 8 GB of RAM to a 3.1 GHz and 16 GB of RAM. I noticed something very strange which is that 1) when I am dong very basic tasks such as downloading something for the new MacBook Pro, it occupies 6 GB of memory used and 2) the CPU usage seems to be high compared to my MacBook Pro with 2.7 GHz when doing the same thing (i.e.: downloading same sized files and size).
Why is this the case? Most curiously, I'm wondering why the memory used for the new MacBook Pro is at 6 GB when simply downloading something.
Best Answer
It is rather difficult to compare a fresh 'cold' new system with a 'warm' fully synchronized and updated one. New Macs have a lot of catching up to do; iCloud service syncing and system patches being two of them.
On the other hand OSX - and every other OS really - chooses a healthy part of the available RAM (real, physical memory) above swapping to disk (virtual memory) for obvious reasons. Having 8 more Gigs available probably decreased your swap file by a couple gigs. Granted, swapping to those post-2013 SSD's is reasonably fast, but no (or less) swapping is always faster (and better for your battery).
Chances are high your increased RAM usage is part of those 2 reasons.