Cooling is the crux of Corsair's new Dominator modules, and there's more to the equation than forced airflow and a flashy clip-on heatsink. The actual DIMM design has been tweaked for more effective heat dissipation, allowing for higher speeds with tighter timings than we've seen from other DDR2 modules. Read on to see just how far we were able to push Corsair's Dominators and what it takes to keep them cool.
Rethinking DIMM cooling
Module makers like Corsair populate their DIMMs with memory chips manufactured by others, and in most cases, they draw from the same pool of chips as their competitors. That doesn't leave much room for product differentiation on the chip level, but careful chip selection, module design, and cooling can squeeze higher performance from what is essentially the same silicon that everyone else uses.
For its Dominator modules, Corsair has rolled out a new DIMM design that incorporates Dual-path Heat Xchange, or DHX for short. Memory modules traditionally dissipate heat from the surface of memory chips through simple metal plates on either side of the DIMM. However, according to a thermal application document (PDF) published by memory chip maker Micron, a significant amount of heat is generated by the memory module's circuit board. To help dissipate that heat, Corsair extended the ground plane upwards, effectively creating a second heatsink on each side of the board.
This second pair of heatsinks (silver in the picture above) is sandwiched between more traditional heat spreaders that cover the memory chips. Both sets extend half an inch above the top edge of the board, and a comb-like pattern of slits provides additional surface area while allowing for increased airflow across the modules.
Speaking of airflow, some of Corsair's Dominator modules also come equipped with an auxiliary cooling unit that clips onto a motherboard's DIMM slots. The unit features a trio of 40mm fans tied to a standard three-pin fan header that users can plug directly into their motherboards. Ideally, that motherboard fan header will feature some form of arbitrary or temperature-based fan speed control, because the unit itself has no provision for changing fan speeds. Loosening the thumbscrews on top of the unit does allow users to adjust the position of the fans a little, though.
Only two of Corsair's Dominator offerings requires the auxiliary cooling apparatus, and as one might expect, it's the more exotic modules that need extra cooling.
The lower latency Dominator variants come with the cooling unit, although it's also being sold separately by some online retailers. Note that the modules that require auxiliary cooling also have higher voltage requirements than those that don't.
All of Corsair's Dominator modules support Enhanced Performance Profiles (EPP) and come in 2GB pairs—1GB per module. There isn't much point to offering lower capacities with such a high-end product, and we've yet to see higher density modules running anywhere close to these speeds.
Today we'll be focusing our attention on the jewel of the Dominator lineup: the TWIN2X2048-8888C4DF rated to run at 1111MHz with 4-4-4-12 timings. We also got our hands on a couple of TWIN2X2048-9136C5D modules designed specifically for Nvidia's new nForce 680i chipset. The 9136C5D DIMMs aren't listed on Corsair's web site, but they're rated for operation at 1142MHz with 5-5-5-15 timings on the nForce 680i SLI.
Installation and clearance
Installing the Dominators is a simple affair. Modules snap into place like any others, and the auxiliary cooler easily clips onto DIMM slot retention tabs. Nine inches of fan wiring also ensures that reaching a motherboard's auxiliary fan headers shouldn't present a problem.
Clearance might be a problem, though. Even without the auxiliary fan unit, the Dominators are half an inch taller than standard DIMMs, and the fans add an additional inch and a half at their tallest point. All that extra height could interfere with wider CPU coolers that fan out from the socket.
Of course, compatibility will vary from motherboard to motherboard and cooler to cooler. Any heatsink that hangs over a motherboard's DIMMs slots won't be compatible with the Dominator's auxiliary cooler and may even interfere with the bare modules themselves.