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Dual Channel To The Rescue

Parallel Processing, Part 2: RAM and HDD
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If you want maximum memory performance, you should install two memory modules into two different memory channels to have it run in dual-channel mode. This doubles memory bandwidth by providing a 128-bit data bus.

At a time when memory clock speeds could not be increased much more, the industry decided to widen the memory bus from 64 bits to 128 bits. With the introduction of the AMD Athlon XP and Intel’s second generation Pentium 4 on Socket 478, dual channel memory controllers saw the light of day on contemporary chipsets : Intel’s 865/875, Nvidia’s nForce2, and the VIA KT266A. The technology behind it is rather simple : data is distributed across two separate memory channels to combine their total bandwidth. As a consequence, you need two memory modules, but the benefit is noticeably higher performance.

Dual channel memory controllers were deployed on all subsequent performance chipsets for Intel processors, such as Intel’s 915/925, the 955 and 975 chipsets (with DDR2) and the latest P35 and X38 models. Let’s not forget about Nvidia’s nForce 4 chipset family either. The only difference compared to past chipset families from a memory standpoint are the utilized technology and clock speeds, as well as slight memory tweaks on the enthusiast models (Intel 975X, X38, Nvidia nForce 680i) to further reduce latency. AMD has been integrating the memory controller with all AMD64 processors. Its single-channel versions died together with Socket 754 ; all other architectures on Socket 939 and Socket AM2 are based on dual-channel RAM today.

Is there still a performance advantage today ? Both memory performance and cache efficiency on today’s processors has increased considerably - we’ll find out in the benchmark section. We picked a Core 2 Duo system with low-latency DDR2-800 memory, and benchmarked it in dual channel mode as well as with only a single memory channel. In both cases we used two 1 GB DIMMs by Corsair.

Installing two memory modules into the same channel of the memory controller will force it into single-channel mode.

Every fast Core 2 Duo processor comes with 4 MB of L2 cache, which has a balancing impact on memory performance. In other words : whether you use super-fast or pathetically slow memory still is important, but the impact is less than it was with older processors using less efficient caches.

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