Corsair Dominator PC8888C4 Review - Under the hood

Memory by thorgal @ 2006-11-02

Once every couple of years a product comes along which can be called revolutionary, and has the ability to upset the market. Corsair brought to the market an entirely new line of memory products, called the Dominator series, with exactly this purpose in mind: dominate the high end memory market. In this review we'll try to find out what sets apart this memory, and if it really can be called revolutionary.

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DHX Cooling Technology

A new cooling technology

The one thing that makes this memory quite literally stand out from the rest of the pack, is its heat spreader design. The design is much taller than your average heat spreader, and the fins give them an aura of performance. There has been a lot of talk about heat spreaders the last couple of years, where some claim that they don't make a difference at all, while others swear by it. Actually, besides the important switch from DDR to DDR2 memory, in my opinion the last innovative feature on the DDR front was another heat spreader revamp: the "honeycomb" grille OCZ put on their performance and high performance memory lineup. Now, if two of the most important manufacturers see the need to refine their heat spreader setup, something is definitely up.

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The pronounced new heatsink design, image courtesy of Corsair inc.

As you already know, heat is the enemy of computer technology on all fronts. This is the case for processors, video cards, hard drives; you name it, but this is also true for memory products. When you are able to cool a component efficiently, you can greatly improve the lifespan of the component, but you can also make it go faster. A Dominator kit consists out of 16 memory banks produced by Micron, which in this case are running outside of their rated specifications. The JEDEC specification for DDR2 ram is placed at 1.8V, but in this case the ram must be able to operate at voltages up to 2.2-2.4V. The goal for the Corsair Dominator series was quite clearly to produce high speed memory modules which could still be given a lifetime warranty at these high voltages. To implement this Corsair came up with some new ideas to remove the heat more efficiently from their modules, and named it DHX : Dual path Heat eXchange...

First let's talk about heat dissipation. There are three different ways in which heat can be dissipated: conduction, radiation and convection.

To make it a bit clearer, I'd like to use the comparison of a home heating system. In many cases our homes are heated by radiators, which provide heating based on all three principles. First of all the conduction: the heated water inside a radiator passes through the metal shell of the radiator, which is highly conductive, and passes on heat to the outside of the radiator.

Next up is radiation: you can feel the radiator from a couple of feet away producing heat. In some cases radiation is sufficient to heat a room: temperatures can be below the comfort zone, but you can still feel comfortable because you're in the radiation zone of a heating panel. Finally, we've got convection, which is a derivative of a Latin word which means "moving together". Convection can only happen in fluids, and luckily for us air is a fluid which works rather well. When a fluid gets heated, by passing along warm surfaces, molecules expand and get lighter. Because of gravity the fluid starts moving around "together" and a heat flow is born. Cool air is taken in at the bottom and transported to the top automatically. To take advantage of this natural phenomenon, radiators nowadays are equipped with so called "convection fins", which are able to pass heat very efficiently to the surrounding air, and in this way create a warm air flow to heat our houses efficiently.

Madshrimps (c)Now we can translate the heat dissipation "laws" to our memory kit, and its heatsink. First conduction comes into play: the heat produced by the millions of transistors inside our component gets transported through the memory chip and onto the metal of the heat spreader. Some of the heat is also transported from the memory chips onto the PCB through the electrical connections. A very little bit of the heat is conducted onto our motherboards as well. The reality is however that by conduction, heat cannot be removed: it stays trapped on the PCB or the heat spreader, and cannot go further. As our heat spreader gets hotter, radiation comes into play. The problem is radiation is not that great for removing sufficient heat from our component. Radiation will be able to heat up our PC case a little, which will cool down from the outside, but without moving air, it's not very efficient. Finally, convection is taking place: the air passing around our heatsink will heat up and create a "natural chimney", thus transporting heat away from the modules, and hopefully into the surrounding room.

Of course you'll understand that when we're talking about convection, the heat spreader design becomes very important. If we have a classical heat spreader design, only heat at the outside of the heat spreader can be affected, and in this respect the surface area of the heat spreader is very important. The more surface, the more air that gets heated up, and the more convection that takes place. Convection inside the heat spreaders was mostly ruled out, because air could not circulate inside the heat spreaders, over the PCB. OCZ was the first to try and improve this with their "XTC" heat spreader design. The honeycomb design allows for improved surface area for heat dissipation and improved air movement over the PCB, in this way improving convection.

Now onto our memory product of the day: the Dominator. Corsair did not follow the OCZ path with their heat spreader design, but came up with a very clever design. As you see from the picture to the left, there is more to the heat spreader design than meets the eye. Corsair does not want to talk about heat spreaders any more, but calls them heat sinks, as they do not spread heat, but actually remove it. Corsair implemented a double heatsink into one package: the main heatsink to remove the heat directly from the memory chips, and a second heatsink to remove the heat from the PCB. This heatsink sits inside the other one and they are spaced in such a way that air can move between the sinks. In this way the surface area is more than doubled for the outside heatsink, and by allowing air to move over the PCB and its second heatsink, far more heat can be transported away from the modules.

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A new PCB design, image courtesy of Corsair inc.

To allow for this new design, some more engineering had to be done. To be efficient, the PCB had to conduct heat towards the heatsink, and to accommodate the PCB heatsink, the PCB itself had to be made taller. In the end, the PCB with the electrical design of the XMS2 PC6400C3 was chosen, and made taller. A special thermal pad was then applied to the PCB to help improve heat transition from the PCB onto the heatsink.

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Close-up of the heat sink fins

If you look closely, you'll see that the heatsinks on both sides of the memory module are not connected to each other, so technically we're talking four heatsinks in this case. The heatsinks are made of extruded aluminum, not meshed or stamped aluminum. This means they are essentially made out of one "piece", so there will be no interruption in the metal and the conduction of the heat. The inside heatsinks (for the PCB) is nickel plated to allow soldering; the outside sink is black anodized. All of the four heat sinks (two on each side) are also equipped with fins, further improving the area of dissipation and thus the heat removal.

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Section of the modules, showing the position of the heatsinks, courtesy of Corsair inc.

Now that we looked at the design innovation of the heat sink, one question remains of course: does it work ? Unfortunately we are not able to produce an accurate temperature test environment by ourselves, so we'll have to rely on Corsair to hand over the numbers.

Of course Corsair wouldn't introduce a design without knowing it works, but some figures always come in handy. In its Press briefing, Corsair claims that, without additional air flow (more on that on the next page), the Dominator heat sink improves the chip temperature by 13°C over a module without heat spreaders, and by 3°C over their previous top of the line heat spreader (the one from the pro series).

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more images of the cooling design

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