If you aren’t sure what Mac model you have or what kind of memory it takes, you can get your System Profile through the Apple menu. The profile will tell you what kind of memory and how much memory is in your system.

STEP 1:   Open the Apple menu
Open the Apple menu, and then select About This Mac.

STEP 2:   Select "More Info..."
The About This Mac screen opens. Click the More Info... button.

STEP 3:   Hardware overview
The System Profile screen opens, showing the Hardware Overview. The Hardware Overview provides you with all the information you will need to use the Crucial Memory Advisor tool, such as your Mac model, CPU type/speed, and total memory capacity.

STEP 4:   Current memory information
In the Contents section on the left side of the screen, click Memory. The Memory Slot information appears, showing your current memory configuration. This information helps you determine which slots are filled with which type of memory, and how many slots are still available to install new Crucial memory.