If you’re looking to purchase a new RAM kit – or upgrade your existing one – a question that many times arises is: Can you mix RAM modules?
To achieve both memory compatibility and synchronicity you’ll have to keep some things in mind so that you can assure your system will operate using the best possible memory performance.
In this article, we will answer the question above, and all matters relating to the installation of additional RAM on an already memory-slot-occupied PC system.
We will also provide suggestions for those looking to build a new setup, and who want to plan out the purchase of their system’s memory.
Can You Mix Different RAM Brands?
In short, the answer to this question is: yes.
No matter the brand, speed, and size of the RAM, theoretically you can mix and match RAM in your system; though it may prove to be problematic.
Also, depending on the setup & workload, you may not even notice a difference in performance.
The only RAM characteristic that will certainly cause incompatibility between RAM modules is the memory type. Different generation RAM sticks – like DDR3 vs DDR4 – will not work together.
That being said, there are many additional factors that must be taken into account to ensure satisfactory results – some of which can be inherently luck-dependent.
This is also why it’s generally ill-advised to attempt to build such a setup – but it is possible.
Why can mixing Brands become an Issue?
Each manufacturer develops its RAM sticks differently. They use different memory controllers, different dies, different materials, PCBs, and different custom circuits.
These are all variables that may ultimately prove to be benign, but there are cases where a conflict in these customizations will cause stuttering, crashes, or even a failure to boot the system entirely.
RAM kits (Modules that are sold within the same package) are factory-tested to work synchronously with each other, and not with other RAM brands or models.
Mixing different RAM kits is usually an issue relating to a system upgrade. This means that multiple Dual In-line Memory Module (DIMM) slots will be utilized.
The more slots that are occupied, the higher the chances that these inter-brand hardware conflicts will arise.
Other Factors to Take Into Consideration
It is not just the different brand-defining characteristics that can cause inherent issues relating to the RAM modules, as these complications can be compounded by other factors.
Firstly, the voltage demands of RAM modules will vary. Having two different voltage requirements will cause the more power-demanding RAM unit to be given less voltage than what is necessary to keep it functioning at its full potential.
This does not mean the RAM module will not operate, but rather that it may not do so at its peak frequency and stability.
Single vs Dual Channel Memory
Another factor that can affect performance is the configuration of the memory in the RAM slots.
Single and multi-channel memory platforms operate differently, and though the difference will not affect the majority of users, it can substantially impact some.
For those that have a PC for gaming, browsing, or undemanding workloads, the difference between single and dual channel bandwidths is ultimately negligible.
Depending on the size, and number, of RAM sticks, the memory will be configured into different multi-channel setups.
This can cause a portion of the RAM to operate in single-channel mode if it cannot be paired with other equivalent memory storage.
As mentioned previously, differently sized RAM sticks can become an issue when it comes to the overall memory configuration.
If a larger storage capacity RAM module is paired with smaller storage units, then the memory channels will be paired in an asynchronous manner.
This is also known as Flex Mode.
This asynchronous dual-channel configuration allows the lower capacity storage unit to be paired with half of the larger module’s storage.
For example, if you were to pair an 8 GB RAM stick with a 16 GB RAM stick, then 8 GB of the 16 GB module will be paired in an asynchronous dual-channel configuration with the 8 GB stick.
The eight remaining GB of RAM of the 16 GB stick will operate in single-channel mode.
Benchmarks carried out by Linus Tech Tips show us that, indeed, there is little-to-no impact in performance under this configuration; depending on the workload.
Speed: Frequency & Latency
Where things begin to fall apart when it comes to mixing different RAM kits is the speed of the modules. Although you can mix RAM kits of varying speeds, whether or not they’ll work will be a coin toss.
Even if you configure the kits to run at the speed of the slowest module, issues are still likely to appear. A memory’s speed is dependent on two factors: The RAM frequency and its latency.
The relationship between the two is as follows:
The absolute latency of a RAM stick (measured in nanoseconds) is calculated by multiplying the reciprocal of the clock frequency (in cycles) divided by two.
For example, a RAM kit with a clock frequency of 3,600 MHz and a CAS of 16 cycles will have an absolute latency of 16/(3,600,000,000/2); which equals approximately 8.89 ns. (Of course, you can always use a latency calculator if you wish to avoid doing the math yourself).
This is important because it shows us how the mixed memory units must not only have relevant RAM frequency, but also relevant CAS latency (CL).
For two RAM sticks, this can be accomplished in a relatively easy manner, but occupying three or four DIMM slots is where issues will almost certainly arise.
Why Should You Buy Your Total RAM Capacity in a Single Kit?
Taking all the aforementioned factors into consideration, it is easy to see why many advocate for purchasing identical RAM sticks in a single kit, in order to achieve optimal performance.
Of course, this is easier said than done, as there will come a time when you will want to upgrade your system’s memory, and that entails increasing the RAM’s storage size or speed.
The best way to avoid these upgrade issues is to plan out and purchase your memory depending on what works best for your CPU model and workloads.
Fortunately, there are some guidelines that can help you ascertain what will be the optimal RAM specifications for your CPU.
This way, when you do upgrade, you can simply buy more identical RAM sticks.
Planning Your Memory Configuration
Depending on the manufacturer of your CPU, the optimal specifications will differ.
If you are wondering how much memory you should purchase, it will depend on the workload you wish to accommodate.
For video editing, for example, 32 to 64 GB of RAM is recommended, while for gaming 16 GB will suffice.
For AMD processors, the best RAM speed to aim for will be double the internal frequency of the Infinity Fabric – also known as FCLK or Fclock. This double data rate will assure a level of synchronicity between your CPU and RAM that will achieve optimal performance.
For Zen 2 and Zen 3 CPUs, the FCLK is 1,800 MHz; so a 3,600 MHz CL 16 RAM kit is a future-proof speed metric.
This kit speed has proven to provide better performance than a 3,200 MHz CL 14 kit, despite having a larger absolute latency metric (8.89 ns vs 8.75 ns).
Do note that the FCLK value can be overclocked; so if your workload requires faster frequencies, you can purchase kits that have a double-data-rate frequency of the overclocked FCLK value.
For a full breakdown of the best memory for AMD CPUs, check our relevant article.
Also, it must be noted that Samsung’s B-Die has been proven to be the best RAM-die for AMD processors.
Purchasing RAM sticks for an Intel CPU is also quite simple, as they have been benchmarked and factory-tested at a specific RAM kit speed: 3,200 MHz CL 14.
These specifications are in accordance with Intel’s internal testing, so it is safe to label this speed as the sweet spot for Intel CPUs.
All in all, if you plan on upgrading your PC’s memory, it is always wise to opt for a single RAM kit.
However, it is understandable that this may not always comply with the allotted budget, as well as your current needs.
If you are planning to build a new PC, make sure to purchase future-proof RAM specifications so that upgrading in the future can be a seamless process.
If your PC already has a RAM kit that is slower than you’d like, you can always purchase additional RAM, and experiment with adding it to your PC until you can replace the older memory.
Remember: the more factors in which you can eliminate variation, the better the chances for optimal compatibility will be.
Can you mix DDR3 and DDR4 RAM?
No, you can’t mix RAM Modules from different generations. DDR3 and DDR4 RAM are physically incompatible.
Can you mix different RAM Frequencies?
You can mix RAM Modules with different frequencies, but it might turn out to be problematic. All RAM Modules have to always run at the same frequency, meaning they’ll try to run at the smallest common denominator.
Because different types of RAM modules support specific latencies at different frequencies, though, they might not be able to sync properly, causing stability issues, or preventing you from POSTing or booting your system entirely.
Can you mix RAM Modules with different sizes?
As long as the frequency, brand, latency, and ranks of your RAM modules match, mixing different RAM capacities should pose no issues in most cases.
Over to you
Do you plan on mixing different RAM modules? Has it worked, or been problematic, for you in the past? Make sure to let us know in the comments below!
If you have any trouble with setting up your RAM, you can always ask the experts in our forum as well.