by Rob Williams on October 7, 2008 in AMD-Based GPU
It’s no secret that the HD 4870 is one of the best overall GPUs on the market right now, but with so much selection from vendors, it’s hard to choose the “best” one. Palit has a definite winner with their Sonic Dual Edition though. It’s pre-overclocked, runs 20°C cooler than the reference design and carries no cost premium.
Before tackling our overclocking results, let’s first clear up what we consider to be a real overclock and how we go about achieving it. If you’ve read our processor reviews, you might already be aware that I personally don’t care for an unstable overclock. It might look good on paper, but if it’s not stable, then it won’t be used. Very few people purchase a new GPU for the sole purpose of finding the maximum overclock, which is why we focus on finding what’s stable and usable.
To help find the max stable overclock on an ATI card, we stick to the Catalyst Control Center included with the official driver. Sadly, ATI’s limits are real conservative, so it’s rare when at least the Core clock can’t be totally maxed out, as long as temperatures are kept within check.
Once we find what we feel could be a stable overclock, the card is put through the stress of dealing with 3DMark Vantage’s “Extreme” test, looped three times. Although previous versions of 3DMark offered the ability to loop the test infinitely, Vantage for some reason doesn’t. It’s too bad, as it would be the ideal GPU-stress test.
If no artifacts or performance issues arise, we continue to test the card in multiple games from our test suite, at their maximum available resolutions and settings that the card is capable of handling. If no issues arise during our real-world gameplay, we can consider the overclock to be stable and then proceed with testing.
Overclocking Palit’s Radeon HD 4870 512MB Sonic
The default clocks for the Radeon HD 4870 are 750MHz Core and 900MHz Memory. Palit’s Sonic card, with the help of the toggle, boosts those figures up to 775MHz Core and 1000MHz Memory, which is minor, but an increase nonetheless. ATI’s Catalyst Control Center, sadly, doesn’t allow much more breathing room than that, and I’m sure it’s to do with the fact that the cards normally have very high temps.
Thanks to these low limits, this is one of those times when the sliders could be maxed out and the card still pass the driver’s stability test. So, our final stable overclock is 790MHz Core and 1100MHz Memory. How much benefit does such a small overclock deliver? Let’s let the graph explain:
The differences are minimal, so overclocking the card at all is almost moot. There is little sense in pushing the GPU further out-of-spec when the differences are so minor, you’d never know the difference in real-world gameplay. If ATI’s control center allowed a higher Core MHz, I’m confident this card could handle it.
Regardless of whether or not you plan to overclock, having reasonable system temperatures is always welcomed. Not only will your machine be more reliable with cooler temps, it will likewise not add any unneeded heat to the room you are in (unless it happens to be wintertime and you keep the windows open, then it might be a good thing).
To test a GPU for idle and load temps, we do a couple things. First, with the test system turned off for at least a period of ten minutes, we measure the room temperature using a Type-K thermometer sensitive of up to 0.1°F. The result from this is placed beside the GPUs name in the graph below. Since we don’t test in a temperature-controlled environment, the room temp can vary by a few degrees, which is why we include the information here.
Once the room temp is captured, the test system is booted up and left idle for ten minutes, at which point GPU-Z is loaded up to grab the current GPU Core temperature. Then, a full run of 3DMark Vantage is run to help warm the card up, followed by another run of the same benchmark using the Extreme mode (1920×1200). Once the test is completed, we refer to the GPU-Z log file to find the maximum temperature hit. Please note that this is not an average. Even if the highest point was only hit once, it’s what we keep as a result.
Luckily enough, the room temperature was exactly the same between testing the stock-clocked HD 4870 and Palit’s Sonic “Dual Edition”, and I have to admit… I didn’t expect such stark differences. Palit’s dual-fan cooler on their overclocked card helped lower the load temperature by 21°C over the stock-clocked card using a reference cooler. Likewise, the idle temperature dropped by 13°C.
These results are very impressive, and I have to wonder why ATI themselves ever stick to the same general reference design from release to release. The sad thing is, while Palit gave us a cooler that dramatically drops the core temperature, we are still unable to go far out of spec with our overclocking, which is too bad, because it’s highly likely that the card could handle frequencies beyond what ATI allows with their control center.