Why mixing your PC’s RAM is a recipe for disaster

When the opportunity arises, upgrading your RAM is a great way to boost your PC’s performance. But RAM can be quite a headache to work out sometimes. That’s because it comes in varying generations, brands, speeds, latencies, sizes, and voltages. In fact, with all that to think about, confusion often arises about whether you can even mix and match RAM and make it work at all. So, can you?

Further reading: How long does computer RAM actually last?

Can you mix and match RAM?

The simple answer is YES! Well, as long as it’s the same generation. So, a stick of DDR 5 RAM should work with another stick of DDR 5 RAM even if they have different specifications, but not with DDR 4 or DDR 3 RAM and so on.

The caveat to all that is that you may not get optimal performance if you do mix. In fact, if getting the very best performance is your goal, you’re better off very carefully selecting your RAM to as closely match any existing RAM and your motherboard’s specifications as possible. Here’s why…

Your RAM will run at a slower speed

RAM clock speed is the frequency with which the RAM can access its memory; it’s measured in megahertz and abbreviated MHz. RAM latency, on the other hand, is the time at which it takes the memory controller of your RAM module to start accessing and writing data.

RAM modules with different clock speeds and latencies will work together, but the faster RAM will always be relegated to run at the same clock speed and latency as the slowest of the RAM modules you’ve installed.

That’s not necessarily a disaster for PC gaming.

We explore this in more detail in our PCWorld article, “Does fast clock speed matter for gaming,” where we point to benchmarks that show only a very small uptick in gaming performance (measured by frames-per-second), when a faster RAM module is switched in place of a slower RAM module.

If you install RAM sticks with different speeds and latencies, the faster RAM stick will run at the speed and latency of the slower stick. 

If you install RAM sticks with different speeds and latencies, the faster RAM stick will run at the speed and latency of the slower stick. 
Dreamstime: Believeinme

If you install RAM sticks with different speeds and latencies, the faster RAM stick will run at the speed and latency of the slower stick. 
Dreamstime: Believeinme

Dreamstime: Believeinme

In fact, in one test by Hardware Unboxed which evaluated performance in seven different games, changing up RAM clock speeds achieved performance boosts of between only seven to 11 percent in some games.

Then again, a boost of between seven to 11 percent is nothing to sneeze at if you’re trying to squeeze every ounce of performance out of your gaming rig as possible. So that’s one good reason not to mix RAM.

You could see a slight degradation in performance

Again, you can mix RAM sticks of different sizes and even run an odd number of RAM sticks together, although you really shouldn’t.

Here’s a size example to ponder. Say you had a stick of 4GB RAM installed in your PC, and you go and install another 8GB RAM stick. Once you turn on dual-channel mode, your PC will match 4GB RAM with 4GB of RAM to run 8GB RAM of dual-channel memory.

The remaining 4GB will run in single-channel mode. This means your PC won’t benefit from a full 12GB of RAM running at the same speed and will likely see a small degradation in performance compared to if it had two RAM sticks of the same size installed.

You may have instability issues

Still not convinced? Try this argument on for size. By not mixing and matching RAM, you’re more likely to avoid RAM instability issues – something that’s really going to adversely affect your gaming performance. These issues can take the form of error messages in Windows and crashes or in the worst-case actual damage to your system components.

RAM manufacturers like Crucial talk about these problems on their websites, where they cite better compatibility as a reason they recommend users match RAM brands, speeds, latencies and voltages, especially when overclocking.

That leads me to the last case I’d like to make — a financial one.

RAM users’ handbooks often warn that mixing RAM modules can void your RAM’s warranty. That could mean if something goes wrong, you may not get the help you need or could even end up losing the purchase price of your RAM module altogether if you can’t get a replacement.

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