Does RAM Latency Matter?

System memory is often the forgotten cousin among components when youre building a new PC. A lot of PC builders just buy whatevers out there, as long as it works in their systems. Some enthusiasts take the opposite route. They get expensive ultra-high-frequency or low-latency memory, hoping it will give them a big performance boost.

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Most major memory manufacturers now offer special low-latency memory. Kingston has a low-latency line of its HyperX DDR400 RAM. Crucial offers a high-performance line called Ballistix. OCZ Technologies has sold specialized low-latency RAM for a long time. And an "LL" designation shows up in Corsairs XMS memory line to indicate this characteristic.

You can pay from 30 percent to 100 percent more for these low-latency offerings, but are they worth the extra money? ExtremeTech examines the effects of low-latency memory on two high-end systems to determine its value to PC builders.

When you buy RAM, youll see two main speed ratings listed: frequency (the maximum rated clock rate) and latency. Memory speed is certainly important if youre considering overclocking, but for now were concerned only with latency. Low-latency memory, running at low-latency settings, supposedly speeds up your system without requiring you to overclock it.

Memory latency is almost always designated in one of two ways. Its either a single number denoting the CAS latency, or a string of four numbers denoting several latencies. CL=2.5, CAS=2.5 or C=2.5 would be common "single number" listings for RAM with a CAS latency of 2.5 cycles, for instance. A four-number designation would be something like 3-4-4-8, in which the four numbers relate to CAS – tRCD – tRP – tRAS.

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