All measurements were taken directly at the card, since measuring system performance is not exact enough. After all, different graphics loads affect processor utilization differently, causing system power to fluctuate.
The direct comparison between the GeForce GTX 770 and 680 is especially interesting, since the newer card offers higher gaming performance thanks to its increased clock rates. Is this performance delta also reflected in power consumption? At least when they're idle, both boards draw roughly the same amount of power.
Higher performance isn't free, and we get a first glimpse of that in our gaming workload, where the GeForce GTX 770 slots in between the 680 and 780 once more. That’s pretty much in line with its performance. Still, the GeForce GTX 680 is more efficient overall. We can also infer that the 770 is operating beyond the GK104 GPU’s sweet spot, since gaming performance falls closer to that of the GTX 680.
The GeForce GTX 770 proves much more power-hungry than the 680 in pure compute applications. Interestingly, the older card seems to be running into its hard-wired power target. On the other hand, the 770 only sustains its higher performance level until it hits its own respective thermal target.
As long as the cards don’t exceed their predefined thermal or power limits, they can hit power peaks beyond what their nominal TDP would allow. In practice, you only see those situations rarely, and very briefly at that. Still, don’t forget to take them into account and pick your power supply accordingly.
Effects of the Thermal Limit
Now let’s see what happens when these cards run into their thermal ceilings after crunching away under load for a while. Like the GK110-based GeForces, the 770 has to throttle back its frequency, noticeably impacting power consumption and gaming performance. We can take this as another indication of how well GPU Boost 2.0 exploits more of a GPU's headroom until that thermal threshold is reached, provided the chip is cooled adequately.
And therein lies the rub. Because Nvidia obviously aimed to keep its reference card as quiet as possible, opting for a very conservative fan speed curve, the 770 almost always reaches its thermal limit during longer gaming sessions. Conversely, if Nvidia were to modify the reference design’s fan curve, allowing the card to remain cool enough to prevent throttling, it would have ended up with a much louder product.
A look at any online store is enough to know that add-in board partners are moving beyond the reference design with this launch. On the next page, we will compare the reference card to three partner boards with third-party coolers to see how they fare when it comes to boost speeds. After all, this is the one factor that will determine a card’s performance under a real-world load.