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NVIDIA GeForce GTX 680 2GB Review

Author: SKYMTL
Date: March 21, 2012
Product Name: GeForce GTX 680 2GB
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GPU Boost; Dynamic Clocking Comes to Graphics Cards


Turbo Boost was first introduced into Intel’s CPUs years ago and through a successive number of revisions, it has become the de facto standard for situation dependent processing performance. In layman’s terms Turbo Boost allows Intel’s processors to dynamically fluctuate their clock speeds based upon operational conditions, power targets and the demands of certain programs. For example, if a program only demanded a pair of a CPU’s six cores the monitoring algorithms would increase the clock speeds of the two utilized cores while the others would sit idle. This sets the stage for NVIDIA’s new feature called GPU Boost.


Before we go on, let’s explain one of the most important factors in determining how high a modern high end graphics card can clock: a power target. Typically, vendors like AMD and NVIDIA set this in such a way that ensures an ASIC doesn’t overshoot a given TDP value, putting undue stress upon its included components. Without this, board partners would have one hell of a time designing their cards so they wouldn’t overheat, pull too much power from the PWM or overload a PSU’s rails.

While every game typically strives to take advantage of as many GPU resources as possible, many don’t fully utilize every element of a given architecture. As such, some processing stages may sit idle while others are left to do the majority of rendering, post processing and other tasks. As in our Intel Turbo boost example this situation results in lower heat production, reduced power consumption and will ultimately cause the GPU core to fall well short of its predetermined power (or TDP) target.

In order to take advantage of this NVIDIA has set their “base clock” –or reference clock- in line with a worst case scenario which allows for a significant amount of overhead in typical games. This is where the so-called GPU Boost gets worked into the equation. Through a combination of software and hardware monitoring GPU Boost fluctuates clock speeds in an effort to run as close as possible to the GK104’s TDP of 195W. When gaming, this monitoring algorithm will typically result in a core speed that is higher than the stated base clock.


Unfortunately, things do get a bit complicated since we are now talking about two clock speeds, one of which may vary from one application to another. The “Base Clock” is the minimum speed at which the core is guaranteed to run, regardless of the application being used. Granted, there may be some power viruses out there which will push the card beyond even these limits but the lion’s share of games and even most synthetic applications will have no issue running at or above the Base Clock.

The “Boost Clock” meanwhile is the typical speed at which the core will run in non-TDP limited applications. As you can imagine, depending on the core’s operational proximity to the power target this value will surely fluctuate to higher and lower levels. However, NVIDIA likens the Boost Clock rating to a happy medium that nearly every game will achieve, at a minumum. For those of you wondering, both the Base Clock and the Boost Clock will be advertised on all Kepler-based cards and on the GTX 680 the values are 1006MHz and 1058MHz respectively.

GPU Boost differs from AMD’s PowerTune in a number of ways. While AMD sets their base clock off of a typical in-game TPD scenario and throttles performance if an application exceeds these predetermined limits, NVIDIA has taken a more conservative approach to clock speeds. Their base clock is the minimum level at which their architecture will run under the worst case conditions and this allows for a clock speed increase in most games rather than throttling.

In order to better give you an idea of how GPU Boost operates, we logged clock speeds and Power Use in Dirt 3 and 3DMark11 using EVGA’s new Precision X utility.



In both of the situations above the clock speeds tend to fluctuate as the core moves closer to and further away from its maximum power limit. Since the reaction time of the GPU Boost algorithm is about 100ms, there are situations when clock speeds don’t line up with power use, causing a minor peak or valley but for the most part both run in perfect harmony. This is most evident in the 3DMark11 tests where we see the GK104’s ability to run slightly above the base clock in a GPU intensive test and then boost up to even higher levels in the Combined Test which doesn’t stress the architecture nearly as much.


According to NVIDIA, lower temperatures could promote higher GPU Boost clocks but even by increasing our sample’s fan speed to 100%, we couldn’t achieve higher Boost speeds. We’re guessing that high end forms of water cooling would be needed to give this feature more headroom and according to some board partners, benefits could be seen once temperatures hit below 70 degrees Celcius. However, the default GPU Boost / Power offset NVIDIA built into their core seems to leave more than enough wiggle room to ensure that all reference-based cards should behave in the same manner.

There may be a bit of variance from the highest to the lowest leakage parts but the resulting dropoff in Boost clocks will never be noticeable in-game. This is why the boost clock is so conservative; it strives to stay as close as possible to a given point so power consumption shouldn’t fluctuate wildly from one application to another. But will this cause performance differences from one reference card to another? Again, absolutely not unless they are running at abnormally hot or very cool temperatures.
 
 
 

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