How to select RAM

Photo by Andrey Matveev on Unsplash

Photo by Andrey Matveev on Unsplash

RAM (Random Accessed Memory) Is one of those PC components that often gets overlooked when building or upgrading computers. It's easy to focus on the big heavy components like the CPU and Graphics Cards. But optimal RAM can have a big effect on gaming or computing performance.

In this article, I will give a short description of how you select the most optimal RAM for your computer.


8, 16, 32, 64 or 128GB?

The amount of RAM you need highly depends on the work you perform. For typical gaming scenarios anything more than 32GB is overkill. 16GB is perhaps optimal for a pure gaming setup.

If you run VMs (Virtual Machines) the scenarios changes. Each VM typically needs 4GB of RAM to run Linux distros, but a Windows VM will need more. If you are an IT student or a programmer you should get at least 32GB to be able to run docker containers and VMs in a lab/developer environment without any issues.

I personally run 64GB to enable a full AD (Active Directory) and Linux lab environment for Cyber Security studies. With 64GB of RAM, I have never felt the need for more RAM while working with labs.

Nr of sticks

1,2 or 4?

Most desktop motherboards support 4 sticks of RAM. Typically these RAM slots are split into two channels. These channels should be symmetric. Meaning, you should run memory with the same speed on both channels, and have the same amount of memory in each channel.

Tests performed by YouTubers and bloggers have proved that it's better to have 4 smaller sticks spread out over 4 slots, than 2 larger sticks spread out over 2 slots. In essence, 2x16GB performs worse than 4x8GB for gaming and other tasks. The performance gain is only in the 5% range, but considering the price of larger memory sticks compared to smaller it only makes sense to go for a 4-stick solution instead of a 2-stick solution.

Transfer rate

3200MHz or 4000MHz

Ram speed is tricky. And this is where you can invest money in the wrong place.

The Transfers rate (transfers per second) or amount of Hz, tells how fast the memory can write or read data coming from or going to the CPU. Bigger is better.

This is limited by the CPU of your computer. If you have a Ryzen 9 5950x that only supports max RAM speeds of 3200 MHz, it makes no sense to purchase faster RAM. You will not be able to utilize it. The reason is that the CPU is the component that will be doing all the reading and writing to RAM. Even though your motherboard supports 4000MHz DDR4 memory you will not be able to utilize it with a CPU that only supports 3200MHz DDR4.

Check the documentation of your CPU to find the memory speed limitation.


CL20 or CL14?

CL or CAS Latency (Column Address Strobe Latency) is a simplified value to tell how fast the memory will be able to select a memory address before reading from or writing to it.

The CL rating is measured in Clock cycles. In other words, how many clock cycles the RAM needs before selecting the correct memory address and starting to send data stored in that address back to the CPU. Smaller is better.

Memory is stored in address grids placed on a grid with columns and rows. The memory address is therefore physically placed on a row/column address similar to a cell in an excel spreadsheet.

The difference between Transfer rate and CL could be compared to Hz being the engine power of a car, and CL is the reaction time of the driver. When the transfer rate is equal, the CL rating will be the performance driver.

Please note that it is possible to have a low transfer rate (MHz) and low CL rating RAM outperform a high transfer rate and high CL rating RAM.


TL;DR - What to do?

A simple step-by-step to select the best RAM for your PC are:

  1. How much memory do you need? Buy that amount of total RAM.
  2. How many RAM slots does your motherboard have? Take the amount of memory you need spread out over that many RAM sticks.
  3. How fast is the max memory speed of your CPU? Buy RAM with that speed.
  4. What is your budget? Use a good online store that allows you to select the CL rating optimized for your budget.

I think that a good rule of thumb is to never spend more money on RAM than on the CPU. RAM can have a 10-15% effect on game framerate. The return on investment when shopping RAM can be pretty low compared to graphics cards and CPU upgrades. But if neither the CPU nor GPU utilization is maxed out in games, it may be bottlenecked by the RAM speed.