Comparing 3200 MHz CL16 and 3600 MHz CL18 RAM: Frequency vs. Latency

When comparing RAM specifications, both frequency measured in MHz and CAS latency CL are important factors that influence performance. Both aspects play a crucial role in determining the overall performance of your system, so let's explore their significance.

Frequency MHz

Higher frequencies generally allow for faster data transfer rates. For instance, 3600 MHz is faster than 3200 MHz. The higher the frequency, the more data can be transferred per second, which is beneficial for applications that require quick access to large amounts of data.

CAS Latency CL

The CAS latency (CL) is the number of clock cycles it takes for the RAM to respond to a request. A lower CL means the RAM can respond more quickly, which is essential for improving overall system performance, especially in applications that are memory bandwidth-sensitive.

Calculating Effective Latency

To determine which RAM is better, you can calculate the effective latency using the formula:

Latency (ns) (CL / Frequency (GHz)) * 1000

Example Calculations

Let's calculate the effective latency for the two RAM configurations:

For 3200 MHz CL16:

Frequency 3200 MHz 3.2 GHz Effective Latency (16 / 3.2) * 1000 5000 ns

For 3600 MHz CL18:

Frequency 3600 MHz 3.6 GHz Effective Latency (18 / 3.6) * 1000 5000 ns

Conclusion: In this case, both RAM options have the same effective latency of 5000 ns. However, the 3600 MHz RAM has a higher frequency, which can provide better performance in certain applications, especially those that are memory bandwidth-sensitive.

More on DDR4 Timings and Their Calculation

DDR4 timings are based on the memory operating speed, which is half of the declared 'speed'. For instance, 3600 CL18 means that the real operating speed is 1800 MHz. The calculated latencies are simple:

(Latency 1 / Speed / 2, in nanoseconds)

Latency Calculations

Let's calculate the latencies for both memory types:

3600 CL18:

Speed 3600 MHz 1800 MHz Latency 1 / 1800 * 1000 0.01 us or 10 ns

3200 CL16:

Speed 3200 MHz 1600 MHz Latency 1 / 1600 * 1000 0.00625 us or 6.25 ns

Key Points:

While both memories have the same effective latency of 5000 ns, 3600 CL18 transfers data a bit faster because it operates at a higher frequency. However, this difference in frequency does not necessarily mean a 12% overall performance increase. The speed difference is more about data transfer speed than overall performance. The time needed to locate data in memory remains the same for both types of RAM, but the 3600 MHz RAM transfers data faster per operation.

The Importance of Memory Internal Structure

The internal structure of DDR4 memory is crucial, and having more banks and bank groups contributes significantly to better performance. For example, fast RAM is often 8GB DIMMs because they have multiple banks and bank groups that allow for more operations to be scheduled in parallel. This parallelism makes DDR4 memories faster and more efficient.

In conclusion, while both 3200 MHz CL16 and 3600 MHz CL18 offer similar effective latencies, the higher frequency of the 3600 MHz RAM can make it a better choice for applications that require faster data transfer rates. Ultimately, the decision should be based on specific use cases and the system's overall performance requirements.