RAMing speed: Does boosting DDR4 to 3200MHz improve overall performance?

DDR4 officially debuted on the desktop in 2014, with the launch of Intel’s Haswell-E, but 2015 is when we should start to see the standard go mainstream. We’ve previously discussed how increases in DRAM clock don’t necessarily translate into increased overall performance — DDR3-2133 has better latency, for example, than DDR4-2133 — but conventional wisdom says that this trend decreases, in the long term, as the new RAM standard becomes faster.

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Now, a new report from Anandtech tests to see how a modern Haswell-E platform’s performance increases with improvements to clock speed. The site tested multiple DDR4 kits at both DDR4-2133 and DDR4-3200.

Benchmark results — why doesn’t DRAM scale?

As Anandtech’s benchmarks show, the benefits of moving from DDR4-2133 to DDR4-3200 are tiny. The vast majority of consumer applications and games show gains of 0-5%. To be clear, Anandtech does find a few applications where this trend gets bucked — minimum frame rates are up a touch in several titles, particularly in SLI testing, and there’s one benchmark, the Redis memory key-store test, where moving from DDR4-2133 to DDR4-3200 gives a relatively huge benefit of 16% for a 50% clock rate boost. These gains, however, are erratic and unpredictable. The Redis test is designed to benchmark an online application database, and explicitly depends on high memory bandwidth and CPU performance. Outside of these tests, performance mostly doesn’t improve from faster main memory — so why not?

First, there’s the fact that modern CPUs and software are all designed to hide or diminish the impact of latency (how long it takes the CPU to retrieve data) as opposed to stressing bandwidth (how much information an application can transfer at the same time). In the early days of computing, when CPUs had very small L1 or L2 caches, main memory latency and bandwidth had huge impacts on performance since they dictated how quickly the CPU could retrieve and execute new data.

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