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.
Our testing methods
All tests were run at least twice, and their results were averaged, using the following test systems.
|Processor||Core 2 Duo E6700 2.67GHz|
|System bus||1066MHz (266MHz quad-pumped)|
|North bridge||Nvidia nForce 680i SLI SPP|
|South bridge||Nvidia nForce 680i SLI MCP|
|Chipset drivers||ForceWare 9.53|
|Memory size||2GB (2 DIMMs)|
|Memory type||Corsair TWIN2X2048-8500C5 DDR2 SDRAM||Corsair TWIN2X2048-8888C4DF DDR2 SDRAM||Corsair TWIN2X2048-9136C5D DDR2 SDRAM|
|CAS latency (CL)||4||4||5|
|RAS to CAS delay (tRCD)||4||4||5|
|RAS precharge (tRP)||4||4||5|
|Cycle time (tRAS)||12||12||15|
|Audio codec||Integrated nForce 680i SLI MCP/ALC885 with Realtek HD 1.47 drivers|
|Graphics||GeForce 7900 GTX 512MB PCI-E with ForceWare 91.31 drivers|
|Hard drive||Western Digital Caviar RE2 400GB|
|OS||Windows XP Professional|
|OS updates||Service Pack 2|
Thanks to Corsair for providing us with memory for our testing. 2GB of RAM seems to be the new standard for most folks, and Corsair hooked us up with some of its 1GB DIMMs for testing.
Also, all of our test systems were powered by OCZ GameXStream 700W power supply units. Thanks to OCZ for providing these units for our use in testing.
We used the following versions of our test applications:
The test systems’ Windows desktop was set at 1280×1024 in 32-bit color at an 85Hz screen refresh rate. Vertical refresh sync (vsync) was disabled for all tests. Most of the 3D gaming tests used the Medium detail image quality settings, with the exception that the resolution was set to 640×480 in 32-bit color.
All the tests and methods we employed are publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.
Overclocking and performance
The Dominators run at relatively high clock speeds by default, but we wondered if it might be possible to push them even harder. Using our EVGA nForce 680i SLI motherboard, we were able to crank the TWIN2X2048-8888C4DF modules up from a stock speed of 1111MHz to a whopping 1245MHz with 4-4-4-12 timings. The DIMMs were perfectly stable at that speed with a 2T command rate, even under load, although the auxiliary cooling fan was required. We tried pushing the 8888C4DFs beyond 1245MHz, but even with extra voltage, they weren’t stable under load and would often refuse to boot Windows.
Our TWIN2X2048-9136C5D modules weren’t quite as happy at higher speeds, only hitting 1200MHz before instability reared its ugly head. The DIMMs were solid running at 1200MHz with their default voltage, though, and they didn’t need the Dominator cooler.
Overclocking success is never guaranteed, so your mileage may vary. Still, we couldn’t resist throwing a few benchmarks at our DIMM configurations to gauge performance. We included a set of Corsair TWIN2X2048-8500C5 modules running at 800MHz and 4-4-4-12 timings for reference, since that’s what we’ve been using for all our Core 2 motherboard reviews. We also have results for the 9136C5Ds at their default 1143MHz and overclocked to 1200MHz. Scores are in for the 8888C4Ds at 1067, 1143, 1200, and 1245MHz, all with 4-4-4-12 timings.
Surprisingly, the 8888C4D’s tighter timings don’t give it much of an edge in Sandra or Cachemem’s bandwidth tests. Turning up the clock speed definitely improves performance, though.
Things get a little more interesting in Cachemem’s latency test, where tighter timings definitely lower access times. Higher clock speeds help, too. Nanoseconds might not seem like much, but with today’s processors chewing through billions of instructions per second, a nanosecond is a virtual eternity inside a modern PC.
Of course, quicker memory latencies and greater bandwidth only improve application performance if that application is memory-bound. Many are not, and as our Quake 4 timedemo neatly illustrates, bottlenecks often lie elsewhere.
Noise levels were measured with an Extech 407727 Digital Sound Level meter four inches from the top of our open test bench with and without the Dominator’s auxiliary cooler.
Even with the Dominator cooler spinning at full speed—unimpeded by automatic or manual fan speed throttling—noise levels are only a decibel and a half louder than without the fan installed. Whether you’ll notice the difference very much depends on just how quiet your system is to start, but exceptionally low noise levels and extreme overclocking rarely go hand in hand.
Corsair’s Dominator TWIN2X2048-8888C4DF modules are pretty scarce online. Our own price search engine only turns up one retailer, and they’re out of stock. None of the usual suspects, including Newegg and ZipZoomFly have stock of the exotic models, either. But maybe that’s not such a bad thing. The TWIN2X2048-8888C4DF kit is listed between $650 and $700 online, which is several times the cost of 2GB of more pedestrian memory. Heck, you could even score a GeForce 8800 GTX for that much.
Of course, ultra-high-end offerings like the Dominator rarely make financial sense. They’re image products meant to push the limits of performance, overclocking, and bragging rights. In that sense, the 8888C4DFs are a resounding success. They offer faster clock speeds than other 4-4-4-12 DDR2 DIMMs on the market, and they overclock higher than any other memory modules we’ve tested.
Bragging rights aside, perhaps the most interesting thing about Corsair’s Dominator modules is the DIMM design itself. The speeds we achieved with the modules certainly suggest there is something to the Dominator design, even without the auxiliary cooling fan, and we look forward to seeing how Corsair applies DHX in future products.