Timings and Latency

THE NEXT part of the holy trinity of memory specifications revolves around timings and latency. There’s a ton of them, but the most important one you need to keep in mind is the CAS latency. Referring to the Column Address Strobe, this figure indicates just how many clock cycles it’s going to take for the memory module to access a particular memory location, either to store or retrieve a bit of data held there, ready for processing by the CPU.

That said, this figure on its own doesn’t give you all the information you need. It’s only when you combine it with the memory transfer rate we mentioned above that you get a better picture of just how fast your memory modules are. So, how do we get a figure that makes any sort of logical sense to us consumers? Well, there’s a handy formula that converts CAS latency and MT/s into a real-world latency: Latency = (2,000/ Y) x Z, where Y is your RAM’s speed in MT/s, and Z is your CAS latency.

So, as an example, if we take a 2,666MT/s memory kit, operating with a CAS latency of 15, we get a real-world result of 11.25ns. This tells us exactly the total time it takes for that memory module to access, store, or request a bit of data from a location on the module.

This is where overclocking memory typically comes unstuck. Generally, the higher the frequency, the higher the CAS latency, and as such, real-world performance gains are often slim, unless the rise of that CAS latency is slowed as well. When it comes to the “best” performing memory, what you’re looking for is a kit that has a high frequency, a low CAS latency, and the necessary capacity (see opposite) to do what you want to do.