Your computer’s random access memory, or RAM, is where data is stored while the processor is waiting to crunch the numbers. More is pretty much always better, within the boundaries of your budget and your system (if yours is 32-bit, it’s limited to about 4GB— vastly less than 64-bit PCs can use), though if you use simple applications and aren’t an avid multitasker, you can get away with less. The nice thing about building your own PC: If it turns out you need more later on, memory is one of the easiest things to add.
What to look for?
Type. Memory will only be useful to you if the motherboard supports it; read that section for more information. Each new standard offers some additional speed and features, but not in all situations, so don’t feel as if DDR4 RAM, rather than DDR3, is an automatic must for you if you’re building from scratch. Just remember that RAM is not backward compatible, so DDR4 will not work in a DDR3 slot. The higher the number in a memory’s standard, such as DDR4 2666, the faster it generally is. Faster memory designed for the same slot type will work in a slower slot, but save yourself some money and don’t leave any performance on the table you don’t have to.
Capacity. DIMMs for each memory type come in a variety of capacities, so you can buy what you need and can afford. It’s best to buy at least one chip for each memory channel (three for triple-channel, four for quad-channel), and memory often comes in “kits” to make that easier; and we don’t recommend mixing and matching capacities within any one build. If you see a capacity listed as something like “8GB (2 x 4GB),” this means the total amount of RAM is divided up between a number of chips (in this case, two DIMMs of 4GB each, for a total of 8GB)..
Memory timings. Most memory specs include a series of four numbers, separated by hyphens that provide an at-a-glance way to tell how speedy the memory is. The first number, CAS latency (the amount of time between when the memory controller requests data and when it’s available) is the most significant, and may be listed by itself. The lower the numbers, the faster you can expect the memory to be.
Other specs. Error Checking and Correction (ECC) memory is intended for high-performance systems such as workstations and servers; you will need a motherboard that specifically supports this type of memory if you want to use it (and most ordinary users won’t need to bother). Voltage numbers give you specific information about how the memory uses power, with higher voltages typically meaning speedier RAM—but this is really of use only to performance craving overclockers.