Should I get DDR3 RAM?
If you're looking to build a great system, but don't want to spend as much money on memory as you might on an entire low to mide-range system, DDR3 is likely the choice for you. A considerable amount of CPUs and motherboards are compatible with this generation of RAM, which means you'll be able to build a capable system fairly easily without needing to get all of the latest and greatest hardware. Even with a DDR3 compatible system, you'll still be able to get amazing performance from your PC.
Is DDR3 compatible with DDR2?
The short answer is no. The long answer is that although DDR3 and the previous generation are both 240-pins, they have different socket keys and voltage levels, among other differences. Installing DDR3 RAM into a previous generation motherboard will likely damage both pieces of hardware.
How much RAM do I need?
For most modern users, multitasking is an essential part of how you use your computer. But sometimes we might have one or two applications open that are just memory hogs, and they bring our system down to snail speed. To avoid this unfortunate scenario, it's recommended to install 8GB to 16GB of DDR3 RAM to give your system the headroom it needs to let all of your applications run comfortably beside each other.
Do I need a 64-bit processor to use DDR3 RAM?
You don't need a 64-bit processor in a DDR3 compatible system, however, to really get the biggest bang for your buck, it's highly recommended. If you use a 32-bit processor, you'll be strictly limited to only 4GB of RAM.
What are low-voltage and ultra-low-voltage memory modules?
DDR3 specifications call for a standard supply of 1.5V to the memory sticks for proper operation. However, in low-power / ultra low-power builds (such as HTPCs and small form factor PCs) you may want to supply lower voltage and have a lower power consumption. These types of sticks are designed specifically for that purpose.
How do I pick from all the different RAM sticks & kits available?
If you're uncertain what memory you should choose you can always refer to your motherboard's RAM buying guides. Different motherboard manufacturers usually have different makes/models that they specfically recommend for their products. Otherwise you can choose from the various performance characteristics to find what's right for your build. These include clock frequency (measured in MHz) where the the higher the clock rate the faster the capabilities of the memory are. Or you can choose by latency (measured in a CL value) where the lower the CL, the faster the memory can be accessed. You can also choose by asthetics such as the color of the heatsink, shape, built-in LED lighting, etc. to best match your build style.
Regarding DDR3 compatibility - what motherboards can support them?
DDR3 memory has been a standard for a long while and compatibility depends largely on the CPU/Motherboard combination that you are going with. The most common motherboard sockets that accept DDR3 as a standard are listed below. It's important to always check both your CPU and your motherboard memory compatibiliy list to find out what RAM is compatible with your particular specifications:
What is DDR3L memory?
DDR3L memory is the low voltage "next generation" of DDR3 RAM. DDR3L typically operates at 1.35v & 1.25v and is supported by the newer generations of Intel processors (Sandy Bridge, Ivy Bridge, etc) and AMD APUs (FX).
Theoretically this memory can function faster than higher voltage memory because lower voltages can change states more quickly. This memory also uses less power than standard DDR3 memory.
Today's DDR3 RAM sticks are clocked usually between 800 MHz to 2000 MHz - the cheaper brands will usually support 800 MHz but this may not be at all bad if you own an older motherboard. Older motherboards that came out around the time when DDR3 was still very new will usually support only 800MHz so even if you buy a higher clocked RAM it will still run at a slower speed.
You can check your motherboard manual or "Google" the speed that your computer supports. Another thing to remember is that if you already own a lower speed RAM and pair it with a higher one, the speed of the RAM will be reduced to the speed of the lower one.
Memory intensive applications like Photoshop, Autodesk Maya and After Effects use a lot of memory and require faster memory speeds to encode, decode and render the special effects. If you use applications such these or play a lot of High end games like Skyrim and Battlefield, you will definitely need the faster clocked RAMs to ensure that you achieve the best results.
Budget and Applications
Buying an expensive RAM with lots of memory and speed does not make sense if you are just using your computer only to surf the Internet or run office applications. These applications require 3 GB to 4 GB of RAM at the most. The entry level RAMs would suffice for such tasks and you do not need to buy a Corsair Gaming edition RAM for such types of applications. Also, keep your motherboard configuration in mind while choosing your RAM because your RAM is only as good as your motherboard.