Why does my Mac show 3.75GB of RAM when I have 4GB of memory installed?
You may have noticed that some Mac models display 3.75GB of RAM in the Activity Monitor when they have 4GB of RAM installed, but why is this? The answer is simple: your Mac has a GPU that uses shared memory. This means that your graphics card borrows some of the systems memory and uses it exclusively for graphics processing, this kind of GPU with memory sharing is common on the iMac, Mac Mini, MacBook, MacBook Air, and the 13″ MacBook Pro model.
In fact, even if you upgrade your RAM you will continue to have the shared memory amount missing from the available RAM within Activity Monitor, as a result if you had an 8GB upgrade it would show 7.75GB of RAM. This is not an indicator of anything being wrong or of having bad RAM, it’s perfectly normal. The only problem with a GPU borrowing RAM is that you may run out of available system memory faster, but you can easily check to see if your Mac needs a RAM upgrade and whether or not you’d benefit from adding additional memory.
I’ve had multiple people ask me this question, so if you were curious too, now you know.