RAM Timings Explained

RAM Timings Explained

RAM specifications include a series of numbers like 16-18-18-36. These are the RAM timings, and they tell you how many clock cycles it takes for the memory to respond to different commands. Lower numbers mean faster response times, but the relationship between timings and real-world performance is more nuanced than just picking the lowest numbers.

The first number is CAS latency, or CL. This is the most important timing. It measures how many clock cycles it takes for the RAM to deliver data after the memory controller requests it. A CAS latency of 16 means 16 clock cycles. But clock cycles are not a fixed unit of time. DDR5-6000 with CL30 has a lower absolute latency than DDR4-3200 with CL16, because each clock cycle is faster.

The second number is tRCD, or Row Address to Column Address Delay. This is the time it takes to activate a row of memory and then access a specific column within that row. The third number is tRP, or Row Precharge Time, which is how long it takes to close one row and open another. The fourth number is tRAS, or Row Active Time, which is the minimum time a row must stay open.

There are many more timings beyond the main four, called subtimings. These include tRFC, which is the refresh cycle time and has a big impact on performance, and tWR, which is the write recovery time. Motherboard BIOS usually sets these automatically based on the XMP or EXPO profile. Manual tuning of subtimings can improve performance, but it is time-consuming and can cause instability.

For gaming, the most important factor is the combination of speed and CAS latency, often expressed as first word latency. A good rule of thumb is that DDR5-6000 CL30 is roughly equivalent to DDR4-3600 CL16 in terms of latency. For AMD Ryzen systems, DDR5-6000 CL30 is the sweet spot because it matches the Infinity Fabric clock. For Intel, faster speeds like DDR5-7200 or higher can give better performance.