Intermixing 2400MHz and 2666MHz DDR4 RAM on a Core i3 8th Gen: What You Need to Know

When it comes to upgrading your computer's memory, you might wonder if you can mix and match different speeds of DDR4 RAM modules, especially when they differ by just 266MHz. This article aims to clarify the compatibility and performance implications of using 2400MHz and 2666MHz DDR4 RAM on a Core i3 8th generation processor.

Compatibility Basics

The short answer is yes, you can pair a 2400MHz and 2666MHz DDR4 RAM module, but there are important considerations to keep in mind. The key is that the system will run at the lowest common denominator of the two speeds, which in this case is 2400MHz. This means that the higher speed module will not achieve its full potential.

Default Behavior

By default, the two modules will run at the highest JEDEC speed profile that both support. JEDEC, which stands for Joint Electron Device Engineering Council, defines standard memory specifications for different voltages and timings. For 1.2V DDR4 modules, the system will default to DDR4-2400. However, if one or both modules are XMP (Extreme Memory Profile) overclocked at 1.35V, the default speed may be DDR4-2133. This is because XMP profiles are designed to push the speed beyond JEDEC standards.

Manually Setting Higher Speed

If your motherboard’s BIOS allows you to change memory settings, you can manually set the speed to DDR4-2400, the maximum RAM speed officially supported by 8th generation Core i3 CPUs. This feature is more common in custom PCs, gaming PCs, and some high-end gaming laptops. Prebuilt office PCs and most standard laptops typically do not offer this flexibility.

For systems with an unlocked chipset, such as Z370 or Z390 motherboards, you can attempt to set the memory speeds above DDR4-2400 by overclocking the 2400MHz module and the CPU’s memory controller. While DDR4-2666 is likely to work, there's a good chance that DDR4-3200 will be stable as well, though you may need to adjust the voltage or memory timings to achieve this. In some rare cases, DDR4-3600 or even higher might be possible, but with increased risk of instability.

Risks and Benefits

Overclocking RAM can improve system performance, but it comes with certain risks. If you overclock your RAM, you might experience random errors, crashes, or even system instability. This is because RAM overclocking can stress both the RAM and the CPU, especially at higher speeds. However, these risks are generally minor unless you push the limits too far.

It's important to note that while overclocking can improve performance, it can also cause instability or even prevent your computer from booting. If you encounter any issues, clearing the CMOS memory can help you revert your settings to default.

Voltage Considerations

When overclocking, adjusting the voltage is crucial for stability. Most DDR4 RAM should be fine up to 1.45V DRAM voltage, while 8th generation Core i3 processors can handle up to 1.15V IO voltage and 1.25V SA voltage. These numbers are conservative, meaning it is highly unlikely to damage your CPU or RAM by overshooting these values by 0.2V.

Conclusions and Recommendations

While you can pair 2400MHz and 2666MHz DDR4 RAM on a Core i3 8th generation processor, the system will operate at the lower speed of 2400MHz, which means the higher speed module will not reach its full potential. If you need to use the higher speed, you can manually set the speed through the BIOS or overclock the modules, but do so with caution to avoid stability issues. Always check your motherboard manual and BIOS settings to ensure compatibility and to follow the recommended voltage and timing settings.