Choosing RAM when building or purchasing a computer can be confusing. There are many brands, types, speeds, some have metal on the outside, some don’t. To simplify the decision, there are three main factors that one needs to keep in mind to ensure a responsive system…
- Type (examples: DDR, DDR2 DDR3)
- CAS Latency (examples: 5-5-5-15 vs. 7-7-7-20)
- Speed (examples: 800MHz, 1066MHz, 1333MHz)
There are different generations of RAM. DDR2 is the most common in household computers now. It is safe to say most computers purchased in the late 90’s have DDR installed. Most systems in mid to late 2000’s have DDR2. The newest generation of RAM is DDR3. When building a computer or simply upgrading, make sure to check which type of RAM your motherboard supports. Prior to purchasing a motherboard make sure to look at its specifications. They should say something similar to “Memory Supported” or “Memory Type”. If you are simply upgrading RAM in your current system, I will explain an easy method to find out what you currently have and what you can upgrade to at the bottom of this post.
As referenced in my “Computer Analogy” post, RAM is a temporary holding place for data. Small amounts of data are moved from RAM and are used by the processor. RAM has to move this data to the processor in portions or cycles. To help explain, envision RAM as a runner on a track. CAS Latency (CL) equals the amount of laps the runner (RAM) has to run before it is finished. The amount of cycles it takes RAM to move all of the portions of data is CL. When comparing sticks (DIMMs) of RAM, if one stick has a CL rating of 5 and another has a CL rating of 6, the DIMM with the CL rating of 5 has one less lap than the DIMM with a CL rating of 6. This means if the speed (MHz) of the DIMMs are the same, the DIMM with the CL rating of 5 is quicker than a DIMM with the CL rating of 6.
Another factor is the speed, measured in megahertz (MHz), at which that data travels from the RAM to the processor. Continuing with the runner analogy, lets say we have two different runners that have to run the same number of laps (CL 5),obviously the faster runner is going to finish first. If you have two DIMMs of RAM with the same CL rating of 5 (5 laps), both DIMMs of RAM are going to need the same amount of cycles to complete their transfer of data. However, the RAM with the higher MHz speed (faster) is going to finish their transfer of data first.
No heat spreader, top - Heat spreader, bottom
A couple other traits of RAM not mentioned above are: 1) Unbuffered RAM, this simply means that there has been a cycle (lap) reduced off its CAS Latency. If a DIMM of RAM has a CL rating of 5, then it’s unbuffered version would have a CL rating of 4; 2) And the second trait is aluminum plating, aka. heat spreaders… see example on the left. This is an outside cover that helps absorb heat off the DIMMs similar to a radiator on a car. This increases RAM’s longevity and helps keep the RAM cool when overclocking.
Recap: The only time you have to worry about purchasing the correct RAM type that is compatible with your motherboard is when you are building your own system. Complete systems sold by manufacturers already have the correct RAM installed, otherwise the computer would not run. Most of the newer motherboards that support Intel’s newest processors utilize DDR3, the newest generation of RAM. Ultimately, when comparing RAM you want the lowest CL rating with the fastest MHz. Generally, the faster the RAM the more expensive it will be. If you are going to be overclocking your RAM it is wise to purchase DIMMs with heat spreaders because heat is your worst enemy when overclocking.
P.S. – In the second paragraph of this post I mentioned there was an easy way to check what type and how much memory you have. There is a memory scanner by a RAM manufacturer named Crucial. The scanner is an effort to promote their RAM, but the type of RAM it suggests can be purchased from another manufacturer as well. This tool will scan your system, inform you of the amount, type and speed of your current RAM. It will also tell you if you can upgrade and what to
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