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:

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.