Graphics Overclocking: Getting The Most From Your GPU

Keeping Cool (Enough)

Back in its day, ATI’s Radeon HD 2900 XT was a very fast card. It also happened to be a very loud one. ATI took another approach with the Radeon HD 4870, setting its fan to spin only very slowly in 2D mode, making the card much quieter.

The downside was that the GPU tended to idle at temperatures of around 80 degrees Celsius, while also heating up other components inside the computer case. Although ATI’s reference cooler design features an air duct to channel the warm air out of the case, the fan’s low speed meant that there wasn’t actually enough airflow to do this job. The resulting higher ambient temperature meant that the CPU, hard drive, memory, and other components were running a good deal warmer, especially in cramped or small towers with little airflow. Using a CrossFire setup with two cards directly adjacent to one another is practically impossible without another fan blowing onto the cards from the side, since they’ll be so close together that one of them will literally have no space to breathe.

There has also been speculation that motherboard components which are closer to heat sources may suffer an increased failure rate. Since the reference coolers are very mature designs, thanks in great part to their use of heat pipes, and make very efficient use of the space at their disposal, there aren’t really a lot of options. MSI has opted to increase the stock fan speed even in 2D mode. If you own a card made by another company, you’d usually either have to simply put up with the higher temperatures or tinker with the fan speed profile in the card’s BIOS--at your own risk, obviously.

While they do have the advantage of getting a better handle on heat output, especially under full load, MSI’s fan speed profiles also result in a lot of noise. The dual-GPU Radeon HD 4870 X2 featured similar fan profiles, using the same formula: higher fan speeds for better cooling at the cost of higher noise output. However, this card was also plagued by stability issues. Depending on the manufacturer and the driver version, the card could produce crashes or system freezes when the graphics chips reached a temperature of 85 to 96 degrees Celsius. Palit sought to remedy that problem by equipping its Revolution 700 with a monster cooler that makes the card one of the few triple-slot add-in boards. On the upside, the cooler’s twin 80 mm fans ensure that both cooling and noise are no longer an issue.

A very welcome side effect of the increased fan speeds is that they tend to allow higher clock speeds as well, which is why MSI calls its modified versions “OC Editions.” Of course, other companies also offer overclocked models with improved coolers. Indeed, the factory overclocked models are often used for marketing purposes, the implication being that they offer better quality in addition to higher performance, justifying their heftier price tag. For example, Gainward offers “Golden Samples” for a variety of models, while Asus improves on the standard models’ performance with its Smart Doctor tool. PowerColor equips its ATI-based cards with improved coolers and then raises their clock speeds, designating these tweaked variants by adding the letters PCS to their model number. Zotac takes a different tack, dialing up the frequencies while retaining the reference coolers, calling these models AMP-Editions. EVGA calls such versions “Superclocked” and specializes in water-cooled dual GPU cards with increased clock speeds. Sapphire’s cards use their own coolers, dubbed Vapor-X, while HIS adopted Arctic Cooling’s designs for their IceQ series of ATI cards with enhanced frequencies.

Several factors can affect a card’s cooling performance. An air duct that funnels the cooler's warm air out the back of the case is certainly a plus, and most dual-slot reference designs employ this type of design. Aftermarket solutions, on the other hand, tend to re-circulate the cooler’s exhaust back into the case. Their biggest upside is that they have a much larger cooling surface and usually employ heatpipes, offering the GPU optimal thermal performance (especially if there is good air flow through the case). The major drawback is that their exhaust air heats up the other components in your chassis, making them less effective as the ambient air warms up. Even a heatsink armed with dual 80 mm fans will have to start spinning up to audible levels if it’s starved of fresh, cool air.

MSI’s models demonstrate both the advantages and the downsides of such altered cooling solutions. The ATI model built around the Radeon HD 4870 runs much cooler than the reference design and quieter than the versions using MSI’s fan speed profile. Its heatsink employs two large heatpipes to transfer the heat to a multitude of cooling fins, and the cooler’s 85 mm fan is nearly silent in 2D mode. Its main disadvantages are that it doesn’t cool the card’s memory modules and doesn’t expel its warm air out of the case, raising the temperature inside.

The Nvidia model using the GeForce GTX 260 doesn’t offer any improvements when the card operates at default settings. Once you overclock it, though, the dual fan solution begins to show its true potential. While the stock cooler hits a wall at a certain point, the Superpipe cooler can still spin its fans a little faster yet. It also helps that it is able to distribute its heat across five large heatpipes. This design already proved its worth on the GTX 285, and the GTX 260 Lightning adopts it to very good effect. It even cools the memory modules.