What Is CAS Latency?
This is the number of clock cycles that go by, starting from when an instruction is given and ending when the data is available. In general, the lower the CL, the better, within a given data rate of DRAM. If you have DRAM running at a data rate of 2133 MT/s, you will typically see a CL of 9, 10 or 11. The CL9 DRAM typically performs more quickly.
Latency is also the inverse of frequency. The faster something cycles, the less time a single cycle takes. That means that, every time a new memory technology doubles the number of clock cycles, the amount of time it takes each cycle to complete is cut in half. Because of that, six cycles at DDR3-1066 happen in the same amount of time as 12 cycles at DDR3-2133. Lower latency numbers do mean that the memory responds more quickly, but the amount the speed is increased depends entirely on the memory’s frequency.