It seems like your Mac (and some version of Linux, and some versions of Windows) will use all available RAM to cache things it thinks you might use, but the second you need the RAM for something you are absolutely going to use it for it'll give that RAM away.

Now, when you're using all your RAM for "real" things then it will start to swap and page out.

The metric to worry about isn't available memory, but something called "Memory Pressure."

It's a little nebulous to me (and very technical) but 8 is probably enough unless you know you have processe that demand the RAM. (<-song)


http://apple.stackexchange.com/questions/107126/what-scale-or-measure-does-mavericks-memory-pressure-adhere-to

http://newosxbook.com/articles/MemoryPressure.html