Power Consumption And GPU Boost
Clock Rates and Thermal Limits
We already covered GPU Boost 2.0 and, small though they may be, the subtle changes Nvidia made to GeForce GTX 780 compared to Titan. Specifically, we see that both cards start limiting core clock rates once the GPU reaches 60°C, dialing back the performance gains attributable to GPU Boost a bit. This becomes more pronounced on the GeForce GTX 780 as its core temperature rises, though the 780 exhibits much greater and more varied clock speed fluctuations, while the GTX Titan is basically limited to three clock levels. While GeForce GTX Titan practically loses the ability to boost its clock speeds as soon as it reaches its thermal limit, the graph still shows 780’s core frequency spiking upward consistently.
In less demanding applications (including games), the GeForce GTX 780 uses slightly less power than Titan. Although both cards bear the same TDP, this is still somewhat surprising. You'd think that the pared-back hardware would be less power-hungry. The difference are in-line with what we're used to seeing from two similar cards with different amounts of RAM. In other words, it seems that the deactivated hardware blocks on the GTX 780 are still drawing power.
Also curious, the GeForce GTX 780 appears to use more power under full load than the Titan until it reaches its thermal limit. Meanwhile, the bigger card runs into its thermal limit sooner, while still offering more performance. One explanation is that the Titan operates closer to the GK110 GPU’s sweet spot, while the GTX 780 relies on higher clock speeds for its performance.
As long as the cards stay within their predefined thermal limits, they can hit power peaks beyond what their nominal TDP would allow. In practice, you will see these only 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
Lastly, let’s look at what happens when both cards hit their thermal limits after being under load for a while. The GeForce GTX 780’s power consumption drops from 245 to 232 W, while the GeForce GTX Titan only dips by 2 W, from 238 to 236 W. This is another example of how much more headroom GPU Boost 2.0 provides, extracting extra performance as long as the GPU remains cool enough.