One of the ways you can increase the performance of your computer is to upgrade the RAM. How much and what type, however, are dependent on the system. You need to make sure that the RAM you buy is compatible with your system, but sometimes the terminology can be confusing. How can you be certain that you’re buying the correct memory?
First, you need to look up what kind of RAM your computer uses and check for any special requirements your system may have. An excellent tool is a program called Mactracker, which lists every Mac since the Macintosh 128k. Using Mactracker, you can easily find out what kind of memory you need, as well as other useful information such as the graphics processor, types of ports and the maximum version of OS you can install.
As an example, let’s say you have a Mac mini. Mactracker lists 10 different versions of the Mini, so you’ll need to narrow down what model you have. The easiest way is to look on your machine under “About this Mac” and click “More Info…” to open System Profiler. The Model Identifier will tell you which one you have (for our example, I’ll assume it’s a Macmini3,1). Searching that model in Mactracker shows it to be a Mac mini from Late 2009; double-clicking that model brings up information about its system. The tab for Memory/Graphics tells you what kind of RAM it needs and how many slots there are.
Note that it may list two numbers: “Actual” and “Apple.” At the time the system was released, Apple had tested this system with 2GB modules and determined that the maximum RAM possible was 4GB (using 2×2GB modules). However, people have since tested the system with 2×4GB modules and reported that it is possible to use 8GB of RAM.
Here’s an important tip – when looking to upgrade the RAM, bear in mind that some systems require RAM to be installed in pairs. If your computer has two RAM slots and says it has 1GB of RAM installed, it’s a good bet that each RAM slot has a 512M RAM module in it. This is important because if you want to upgrade your system to a total of 2GB, you can’t just buy a single 1GB module and add it to the existing memory; you have to buy two 1GB modules and remove both of the 512M modules. If you are in doubt as to what is installed, check the “Memory” section in System Profiler to see what is installed in each bank.
Continuing with our example, a Mac mini from Late 2009 supports a total of 8GB, and System Profiler says it has 2GB installed (each slot has 1GB installed). 4GB modules have come down in price recently, so why not max it out? Now check the next line in Mactracker, “Type of RAM slots:,” and you’ll see… a bunch of weird numbers and letters. What do those all mean?
RAM comes in many capacities, speeds and sizes. In order to tell which one is which, there are specifications to tell them apart. The first number, in this case PC3-8500, refers to the access time of the memory chips (how fast the chip is able to read or write data). The higher the number, the faster the speed. Note that this number refers to the maximum speed the chip CAN transfer data, not how fast it WILL, so if your system requires 4200 memory, then use 4200 memory; installing 8500 will not make it go faster. However, installing 4200 in a system that requires 8500 will cause the system to crash or not function at all, especially if the speeds of the RAM don’t match. Since many systems support interleaving* (a way of increasing performance by sharing RAM addresses between the two modules), it’s beneficial, but not required, that the modules be identical.
The next thing listed under “Type of RAM slots:” for the Mac mini from Late 2009 is DDR3. DDR stands for “double data rate,” meaning the data can be transferred twice as fast as a standard memory module. The most current revision is DDR3 (double data rate type 3), which is not backwards compatible with DDR or DDR2, so make sure you get the right type for your system.
The final term will say either SDRAM or SO-DIMM. SDRAM is larger and primarily used in desktop “tower” machines such as the Mac Pro or older iMacs. SO-DIMM is a smaller form factor and used in portable devices and new iMacs, including the Mac mini from Late 2009.
*“Interleaving support” means that you will get a slight performance gain by matching the RAM modules. This is more important in systems like the MacBook that do not have dedicated video RAM. If you check the next section under Graphics Memory in Mactracker, it states that the RAM in the Mac mini from Late 2009 is shared with main memory. Since the RAM is being used for both the processor and the video chip, it is definitely to your benefit to take advantage of the performance gain offered by interleaving. This does not have to be enabled; it happens automatically as long as the RAM modules are identical. Apple (and Small Dog) will always try to install RAM in pairs for this reason.
Once you know the type and size you need, check out our RAM Finder page!