[DRAM Basic] What are RAM Frequency and Timings? Which is more important?

These are two critical parameters that significantly impact memory performance.

• Frequency (Speed):
  • Expressed in MHz (MegaHertz) or MT/s (MegaTransfers per second), it indicates how many million data transfers the memory can perform per second. Higher frequency means faster data transfer. For example, DDR4-3200 (3200 MT/s) is faster than DDR4-2400 (2400 MT/s).
  • In DDR5, due to its dual-channel sub-architecture design, the MT/s value is twice the individual memory chip's clock frequency.
• Timings (Latency):
  • Usually represented by a series of numbers, such as CL16-18-18-38. These numbers denote the delay (in clock cycles) required for the memory to perform specific operations. The most crucial parameter is CAS Latency (CL).
  • Lower numbers indicate lower latency and faster memory response. For example, CL16 has lower latency than CL18.
  • Common Timing Parameters:
    • CAS Latency (CL): The delay between when the memory controller issues a read command and when the data is actually available.
    • tRCD (Row-to-Column Delay): The delay between activating a row and accessing a column within that row.
    • tRP (Row Precharge Time): The time required to precharge a row before another row can be accessed.
    • tRAS (Row Active Time): The minimum time a row must remain active for a read or write operation to complete.

Which is more important?

In most scenarios, frequency generally has a more noticeable impact on performance than timings, especially in applications that demand high CPU bandwidth (like gaming). However, ideally, you want both high frequency and low timings.

The optimal performance balance is achieved by finding memory with high frequency paired with relatively low timings. Sometimes, a lower-frequency module with extremely tight timings might offer better real-world latency performance than a higher-frequency module with very loose timings. You can estimate the true latency (in nanoseconds) using the formula: True Latency (ns) = (CL / (Frequency / 2)) * 1000. For instance, DDR4-3600 CL16 (approx. 8.89 ns) often performs better than DDR4-4000 CL19 (approx. 9.5 ns).