Cas latency for RAM measures the delay between a command sent to memory and its execution. Lower numbers mean faster response times.
CAS (Column Address Strobe) latency is part of a larger timing system called CL (CAS Latency). When your CPU requests data from RAM, CL determines how many clock cycles it takes for the memory module to provide that data. For example, DDR4-3200 CL16 means the RAM runs at 3200MHz with a CAS latency of 16 cycles.
| RAM Type | Typical Speed Range | Typical CAS Latency |
|---|---|---|
| DDR4 | 2133MHz - 4266MHz | 15 - 20 |
| DDR5 | 4800MHz - 6400MHz | 30 - 44 |
| LPDDR4 | 1600MHz - 4266MHz | 11 - 19 |
Many assume lower CAS latency always means better performance. However, higher-speed RAM with slightly higher CAS latency can sometimes outperform lower-latency, slower RAM. For instance, DDR4-3200 CL16 might perform better than DDR4-2400 CL14 because the higher speed compensates for the extra cycle.
According to Tom's Hardware, "CAS latency is just one piece of the puzzle. Real-world performance depends on the combination of speed and latency, as well as other factors like motherboard support and CPU capabilities."
CAS latency is often confused with RAM speed. While related, they measure different aspects. Speed (MHz) indicates how many operations the RAM can perform per second, while CAS latency measures the delay before the RAM starts responding to commands.