When assembling or upgrading a computer, we often see memory modules labeled with parameters like “DDR5-6000 CL36” and “DDR5-6000 CL30.” The “6000” represents the memory frequency (MHz), while “CL36” and “CL30” are abbreviations for “CAS Latency,” which is commonly referred to as “timings.”
So, what’s the difference between C36, C30, and C28? How do they affect performance when frequencies are the same? And how should you choose? Let’s discuss this topic in detail today.
Previously written content about memory frequency: 电脑组装那些事
What is CAS Latency (CL)?
Simply put, CAS Latency (CL) refers to the number of clock cycles a memory needs to wait between receiving a read command and actually starting to output data. The smaller this value, the faster the memory responds and the lower the latency.
For example:
- DDR5-6000 CL36: This indicates that the memory needs to wait 36 clock cycles to respond to a read request at a frequency of 6000MHz.
- DDR5-6000 CL30: At the same frequency, only 30 cycles are needed.
Even though the frequencies are the same, a lower CL value results in smaller actual latency (Latency).
How to Calculate Actual Latency?
Many people mistakenly believe that a higher frequency always equates to better performance, but in reality, actual latency = (CL ÷ Frequency) × 2000 (units: nanoseconds, ns). Let’s compare:
| DDR5-6000 CL36 | 6000 | 36 | ((36 ÷ 6000) × 2000) ≈ 12.0 ns |
How to Calculate Actual Latency?
| Model | Frequency (MHz) | CL Value | Actual Latency (ns) |
|---|---|---|---|
| DDR5-6000 CL30 | 6000 | 30 | ((30 / 6000) * 2000) ≈ 10.0 ns |
How to Calculate Actual Latency?
| Model | Frequency (MHz) | CL Value | Actual Latency (ns) |
|---|---|---|---|
| DDR5-6000 CL28 | 6000 | 28 | ((28 ÷ 6000) × 2000) ≈ 9.33 ns |
How is Actual Latency Calculated?
As you can see, the actual latency of CL28 is approximately 22% lower than that of CL36. In latency-sensitive applications (such as gaming, high-frequency trading, real-time rendering, etc.), this difference may result in a perceptible performance improvement.
Is There Really a Big Performance Difference?
In everyday scenarios like office work, web browsing, and video playback, the difference between CL36 and CL28 is almost imperceptible. However, the advantages of low-latency memory become more apparent in the following situations:
- Game Frame Time Stability: Lower latency helps reduce stuttering, especially in CPU-bound games (such as CS2, League of Legends, and Nioh).
- Content Creation & Compilation: Certain workflows that rely on memory bandwidth and latency (like large code compilation, 3D rendering caching) will also benefit.
- Overclocking Potential: Low-latency memory typically uses better dies (such as Hynix A-die, M-die), which are more suitable for further overclocking.
However, it’s important to note that low latency often means a higher price and stricter requirements for motherboard/BIOS compatibility. If your motherboard doesn’t support EXPO/XMP 2.0 or your BIOS is older, you may not be able to stably run CL28 at high frequencies.
So, which one should I choose at 6000MHz?
For most users, especially those pairing it with AMD Ryzen 7000/8000 Series processors, DDR5-6000 CL30 is currently the “sweet spot” configuration:
- The official JEDEC specification recommends a frequency of 6000MHz, and CL30 is the stable timing verified by AMD;
- It offers high value for money, with moderate pricing and good compatibility;
- Actual latency is controlled around 10ns, balancing performance and stability.
If you’re an extreme performance gamer or seeking ultra-high frame rates, and your motherboard supports it well (such as high-end B650/X670 models), you can consider models with CL28 or even CL26, but be prepared to potentially need manual tuning and voltage adjustments.
As for CL36, while it can be used, it’s typically entry-level DDR5 memory with high latency, unless your budget is extremely tight, we don’t recommend it.
Summary
- C36, C30, and C28 refer to the memory’s CAS Latency (Timings); lower numbers indicate smaller latency.
- Under the same frequency, CL28 is approximately 22% faster than CL36 in actual latency, offering greater performance advantages.
- DDR5-6000 CL30 is currently the most balanced choice and suitable for most users.
- For extreme performance, choose CL28; if budget is limited, accept CL36, but weigh latency against price.