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Does Memory RAM Have to Match?
RAM sizes can be mixed, but it’s often not recommended as it can decrease computer performance. It’s recommended to match RAM sticks by the same manufacturer, with the same size and frequency.
RAM (random access memory) is a necessary computer and smartphone component. The job of RAM is to remember computations for a limited amount of time, so that the computer processor doesn’t need to redo the computations every time.
RAM sticks by different manufacturers are usually made out of differing components. RAM from the same vendor can be made out of different components over time.
This is often why RAM sticks are sold in kits of 2x4GB or 2x8GB, to ensure that they are identical and compatible with each other.
Some motherboards are very sensitive to this as it has to manage all the RAM using the same specifications of voltage and speed. This makes it more difficult to manage different sizes or makes of RAM.
Different sizes of RAM can be used together, but for them to perform optimally, the same voltage and controllers should work well with each other, and the motherboard. Usually for this reason, it’s recommended to use the same model in all slots.
The issue you’ll most likely encounter with different RAM sticks is an incompatibility between the two RAM sticks, incompatibility with the motherboard, or a limitation in your motherboard’s design.
Things to consider when buying RAM outside of kits:
- Speed of memory. A stick at 1600mhz speed and another at 1333mhz speed will cause the 1600mhz stick to be slowed down to match the slowest module.
- Size of memory. An 8GB stick will need 8GB or higher or it won’t work.
- Latency of memory. Latency of CAS 9 and CAS 11 will mean the computer runs at CAS 11, which is slower.
Dual channel mode can run different size RAM sticks, but it won’t be optimal. For example, a new 8GB stick and an existing 4GB stick will perform as two 4GB sticks running side by side, while the remaining 4GB of the new 8GB stick will run in single channel mode. It’s not as fast as using two sticks of the same size, but it will be faster than before.
Using two same sizes of RAM sticks can yield up to 5% extra speed in dual channel mode without needing extra hardware.
A 5% boost is minimal, but 5% more speed for free is a nice benefit, which is why users are recommended to use identical RAM sticks.
If there are more than 2 slots, 3 sticks can be used as well. One pair will run in dual channel mode, while the last stick will be in single channel mode.
For a guaranteed run, the exact same model and manufacturer of RAM stick should be used. Latency and voltage should also be the same for the best speed compatibility.
Disadvantages of Mixing RAM
- Lower speed as the system downclocks to match the stick with the lowest speed.
- Lower latency because the computer has to match the stick with the lowest latency.
- No dual channel performance benefits if RAM sizes are different.
- Voltages for older modules might not work on newer modules.
- Compatibility issues with the motherboard.
- Stability issues on the system.
To prevent these issues from cropping up, it’s recommended for users to use the same brand, size, speed and latency of RAM sticks for all slots. Users can also enjoy a performance benefit by utilizing the dual channel with the same size of RAM sticks without needing extra hardware.
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.
Is it OK to Mix RAM Speeds?
It is entirely possible to operate two or more RAM modules at different speeds. However, just like mixing brands, you will default to the lowest-performing RAM modules.
For example, let’s say that one set of RAM modules are 16GB CORSAIR DDR4 3200 MHz with a 16 CAS latency. The other RAM module set is a 16GB TEAMGROUP T-Create Classic DDR4 2666 MHz with a 19 CAS latency.
If installed in the same PC, both modules will be reduced to the lowest common denominator, i.e. (2666 MHz) speed and (19 CAS) latency to work together effectively.
Conversely, the CORSAIR DDR 3200MHz with a 16 CAS latency typically costs more and is crippled to a lower usable frequency and latency. In turn, you are not using your RAM to its fullest potential, preventing you from getting the most out of your RAM.
Simply put, you just paid a price premium for a performance boost you cannot use.
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.