How many modules should I get?
If you want 16GB of RAM, you could be tempted to buy one 16GB module. Makes sense, right?
Well, if you did that, you would be sacrificing something called dual-channel mode (or quad-channel if you went for 4 x 4GB). Buy buying two 8GB modules, you get the same amount of memory but the bandwidth is doubled. Rather than only having access to one stick, your processor can now access two simultaneously. This offers some advantages, such as reduced CPU usage and some frame rate improvements
Choosing the right type.
Unless you are dealing with an old system, DDR4 (Double Data Rate 4) is the current common standard for RAM. It is the 4th generation of the DDR family and offers greater data transfer rates and capacity per module, as well as running on a lower voltage, making them more energy efficient.If you have an older motherboard, it may use DDR3 modules. You cannot use DDR4 on these boards as they simply won't fit.
DDR5 is now available to buy, but only compatible with the latest processors and motherboards. DDR5 offers faster speeds at a premium price, but that will start to come down as it becomes more popular.
What speed should I buy?
When choosing RAM, you should look out for its speed rating, in Megahertz (Mhz). A module of 2400Mhz RAM will be slower than a stick rated at 3200Mhz, for example. You must make sure that your motherboard supports the frequency of the RAM you choose. You can do the buy checking the specifications of your motherboard before buying.
Anything else?
Actually, yes! The final thing to consider when it comes to performance is the CAS (Column Access Strobe) latency. It is the delay between the CPU making a request and the RAM responding.
To find the CAS of your RAM, look for a string of 4 numbers listed in the name, in this format:
15-16-16-35
The first number is you CAS. What you want is the lowest number possible. DDR4 has a range of 15 to 19. The lower the CAS, the higher the price.
As an example of what CAS means, let's take a look at the formula needed to show you the latency of your RAM:
(CAS latency/RAM clock speed) x 2000 = latency in nanoseconds
If you have a CAS of 16 and a speed of 3200Mhz, your latency would be:
(16/3200) x 2000 = 10 nanoseconds.
Compare that to a CAS of 19 x 3600Mhz:
(19/3600) x 2000 = 10.5 nanoseconds.
Despite having a faster clock speed, the 3600Mhz, module is slower than the 3200Mhz module, all thanks to the CAS. Hopefully this demonstrates why it is an important consideration.