In Search of True DDR2 Bleeding Edge Memory

Two DRAM Sides Are Better Than One

As PC enthusiasts know, many modules of the same size come in both one- and two-sided versions. It's a good idea to buy double-sized modules whenever possible, because they have a built-in speed advantage over their single-sided brethren. In addition, there are now numerous Intel chipsets with DDR2 support under development that will treat both sides of a memory module together in a kind of RAID relationship. The resulting speed advantage is on the order of 2%, and was measured in the THG labs. In fact, using four single-sided memory modules doesn't help, and doesn't produce the same effect. By comparison with double-sided memory modules, measured performance actually decreases when using single-sided modules.

The chipset memory control works with two single-sided modules in dual-channel use.

With two double-sided modules, the Intel chipset can actually run four sides (memory banks) in parallel.

An overview of speed improvements based on chip size and placement:

Swipe to scroll horizontally
Sides Speed (CL 5.0-5-5-15) FSB 1066
SidesReadWriteLatency
4 (2 Module)7320 MB/sec2157 MB/sec83.9 ns
2 (2 Module)7225 MB/sec2118 MB/sec83.5 ns
4 (4 Module)7058 MB/sec2093 MB/sec89.3 ns
3 (3 Module)5130 MB/sec1698 MB/sec84.2 ns
1 (1 Module)5123 MB/sec1672 MB/sec84.4 ns
SidesReadWriteLatency
4 (2 Module)142.9%129.0%99.4%
2 (2 Module)141.0%126.7%98.9%
4 (4 module)137.8%125.2%105.8%
3 (4 module)100.1%101.6%99.8%
1 (1 module)100%100%100%

It was also interesting to observe that double-sided 512 MB modules were slightly thinner although they were produced with 110-nm fab technology. However, this also results in a somewhat lower potential for overclocking. In any case, our measurements show that speed appears to be independent of the number of memory modules paired up on a motherboard. A PC enthusiast can therefore populate a motherboard with either 2 or 4 GB of DRAM, without really impacting performance.

Some DDR2 modules come with heatsinks attached. These only look good, because their memory chips use either 110-nm or 90-nm processes and don't need additional cooling.

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