Capacity:2X 4GB 1066MHz While at first glance, it may be in your best interest to shop around. Know that when you purchase RAM from Komputerbay, you're getting Grade-A brand name computer memory. Cheap computer memory, while possibly being compatible, can cause system crashes, error codes in your computer, and even damage to your motherboard! Other sellers may offer you similar looking products for a few cents or a dollar less, but here's the scoop on why: they sell cheap-grade memory and they don't test the modules before shipping! This ends up costing you time and money. Trust when you buy from Komputerbay, you are getting top of the line product from a top of the line company. We test every module before it leaves the building, and back all of our purchases up with a LIFETIME WARRANTY! 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, 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 ( make sure yours is DDR3 1066MHz ). This information helps you determine which slots are filled with which type of memory, and how many slots are still available to install new memory.