RAM timings, CAS latency and dual channel

In short: For memory, clock (MT/s), latency (CL) and the number of channels count. Two modules in dual channel double the data width and often bring more than a few MHz of clock.

In more detail: CAS latency (CL) says how many clock cycles the memory needs after a read request until the answer. In absolute terms what counts is time in nanoseconds, not the number alone.

In Depth

• Absolute latency: CL / (clock in MT/s / 2) · 1000 ns. DDR5-6000 CL30 → 30 / 3000 · 1000 = 10 ns, DDR4-3200 CL16 → 10 ns. Same latency, but DDR5 delivers more bandwidth.
• Timings: CL-tRCD-tRP-tRAS such as “30-36-36-76”. Lower values are faster.
• Dual channel: Two modules in the right slots (see manual, usually slots 2 and 4) talk to the CPU over two 64-bit channels. A single module slows especially games and integrated graphics noticeably.
• Rank: More ranks can add performance, but also lower the reachable clock.
• Profiles: Enable XMP/EXPO, otherwise memory runs at slow default values.
• Stability: Check with MemTest86. See DDR to DDR5.

See also: ECC memory