AMD Radeon HD 7870 & HD 7850 Review

Author: SKYMTL
Date: March 3, 2012
Product Name: Radeon HD 7870 & HD 7850
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PowerTune Technology

One of the largest challenges GPU manufacturers face is the rapid increase in the power consumption of their higher-end ASICs. NVIDIA’s solution to cut consumption and TDP in their GTX 500-series was a combination of input current monitoring and upgraded heatsinks along with application detection. AMD meanwhile took a different path with their PowerTune technology. It uses a complex set of concurrent calculations to determine on-the-fly TDP levels so clock speeds can be adjusted once the card reaches a pre-determined maximum thermal design power level.

The entire point of PowerTune is to allow AMD to strike a delicate balance between power consumption, thermals and clock speeds. If such a middle-man didn’t exist, the clock speeds many AMD GPUs would have been significantly lower since there would have been nothing to keep TDP in check. As one might expect, PowerTune makes a comeback in the Pitcairn cores and it still behaves in the same way as before.

A typical GPU will likely be used in any number of applications but its primary focus will usually be upon one thing: entertainment. While there are several synthetic benchmarks which cause a graphics card to consume copious amounts of power, most typical games will never even begin to approach these levels. As such, AMD has focused their PowerTune technology upon scenarios which put unrealistic loads upon the GPU rather than games. Since most of us don’t sit around all day benchmarking with 3DMark, this is good news.

Unfortunately, depending on their rendering methods there may still be the odd game which will be caught up in the crossfire and have its performance capped but we will be tackling this potential issue in a later section. It is just important to remember that AMD has tuned this technology to deliver the best gaming performance while weeding out potential power viruses.

As AMD describes it, this new technology is simply used to contain power consumption in such a way that the actual TDP of a given product will in effect determine clock speeds. Instead of letting the card run amok for the few seconds of absolute peak consumption that will likely occur every now and then, PowerTune caps power draw through clock speed modification. After the peak periods are concluded, clock speeds along with performance will return to normal.

This may all sound like doom and gloom for overall performance but PowerTune is actually designed for a worst-case scenario rather than a typical usage pattern. The algorithm to determine implied power consumption is based upon an extremely high leakage ASIC operating with 45 degree inlet temperature. Remember that high temperatures increase power draw in transistors so this ensures products are not artificially capped in lower temperature scenarios. Since TDP is the determining factor here, if you keep your card cool within a well ventilated case you should in theory never see PowerTune kick in while gaming. According to AMD, it has also allowed them to drastically increase the clock speed of their cards since PowerTune allows for better TDP predictability.

ZeroCore Power

One of the issues with most modern graphics cards is their power consumption when not actively driving 3D graphics content or accelerating certain applications. Even if your monitor is turned off, the only way of conserving electricity is to put the system to sleep or allow it to hibernate. Granted, when in idle mode a GPU doesn’t consume all that much power but a constant 30W over long periods of time can sure add up on a monthly power bill. This is where ZeroCore Power steps into the equation.

The basic idea behind ZeroCore Power is to effectively shut down the card during periods when the GPU isn’t outputting an onscreen image. These “long idle situations” are determined by Windows which is programmed to shut off your display after a preset amount of time (you can access it by going into the Display Power Options and choosing when Windows can turn off your display) in order to optimize full system efficiency. AMD’s driver will detect this and put the graphics card into a suspended sleep mode by shutting off the fan and powering down non-essential onboard components. It will then wake back up the moment Windows detects an input and activates the display again.

AMD hasn’t stopped there either. Pitcairn features power saving features like engine clock deep sleep and a DRAM stutter mode (which compresses any residual contents within the framebuffer) in order to further reduce standard 2D power consumption to a mere 10 to 12 watts.

Where ZeroCore Power technology really comes into its own is in Crossfire setups, even though the Pitcairn products are only compatible with dual card setups. Since only one GPU is driving the display at all times, any additional cards are automatically put into ZeroCore mode, even when in standard idle conditions. The result is drastically lower idle power consumption numbers for systems with more than one GPU. Meanwhile, in long idle situations, even the primary graphics card is put into a suspended sleep mode as well.

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