The most common, and the easiest, to answer scenario is when someone has an older system and is building an entirely new rig. For example, you have an older DDR3 system and are planning on building a shiny new DDR4 system – be it AMD’s Ryzen series, Intel’s Z270 or X299, etc. This is the easiest as the answer is “it won’t work”. If you have an ancient rig that uses DDR3 and you want to build a DDR4 system… don’t even bother with DDR3/DDR4 combination motherboards. Bite the bullet and get a good motherboard, an entirely new set of RAM and leave the old system alone.
So let’s narrow down the scenarios where it actually makes sense to even think about reusing RAM. The first is you have an older system and while you want to build a new system a full upgrade is just not in your budget. Instead you want to put a ‘patch job’ on it and try and get by for another year or three before having to budget and build an entirely new rig.
For these types of scenarios, the question you have to ask yourself is what is your goal and what do you have right now? Do you have a system with two 4GB sticks in there and simply want to go to 16GB? Then yes upgrade away. Get two more similar speed sticks and have at it. Try and get the same make and model to reduce issues.
Conversely you have an older rig with 2x4GB and you want to max out the memory. Don’t do it by sticking in 2x8GB and having it reside alongside the 2x4GB set. Yes 24GB is more that 16GB but having odd amounts can be a recipe for problems. It can work, depending on the motherboard, but with the cost of RAM being so cheap simply don’t bother. So if you just want to double the amount of RAM, and can get similar speed and size sticks, go for it. Otherwise sell the small sticks and start from scratch.
These two scenarios cover about 80% of the people who ask us about mix and matching RAM. The other twenty percent falls into new system builders who want to carry over their existing RAM to a new rig, already know that is the same type (e.g. DDR4) but getting new RAM with the same speed is tough, or they found a great deal on some ‘uber speed’ RAM and now are asking for help on how to get it work. So with this 20% in mind lets go over the most common scenarios and how they will usually go.
