When we say that different processors working at different clock frequencies have different power consumption levels, we should keep in mind that their performance is different, too. For example, a processor may be extremely economical but at the same time so slow, that solving even the simplest tasks in systems based on it may take forever. Therefore, processor manufacturers have been actively lobbying the “performance-per-watt” complex parameter that describes the value of each watt of power for the overall system performance.
Estimating the energy-efficiency of an overclocked system is also a very interesting topic. Overclocking not only increases performance, but also affects the power consumption, as we have just seen. Therefore, we decided not to overlook it. however, instead of an artificial “performance-per-watt” parameter, we decided to study a different and more understandable one – the amount of electrical energy necessary for different systems to complete the same calculations. In other words, we decided to measure how many watt-per-hour we would need for typical tests. And the time it takes for these tests to be completed is directly dependent on the CPU speed. I also have to say that “power consumption” and “performance-per-watt” parameters are in inverse relation with one another. In other words, the results we obtained will allow us to draw conclusions about the connection between performance and power consumption.
Very unexpected, don’t you think so? It turns out that despite the growing CPU power needs during overclocking, we often gain rather than lose when it comes to energy consumption. The thing is that overclocking increases not only power consumption, but also performance. As a result, an overclocked system may cope with the same amount of work faster than a non-overclocked one, which produces certain savings right away. However, it is important to remember that if system energy-efficiency is the primary objective, then you shouldn’t get too involved with overclocking. By raising the processor Vcore, you trigger a sharp increase in power consumption, which won’t be compensated by the performance increase, as you can see from our test results. In other words, overclockers will hardly be pleased with their power bill, but it will be OK with those who overclocked carefully, didn’t raise the processor core voltage and kept the power-saving technologies up and running.
The new type of processor load didn’t affect the unexpected regularities that we had uncovered in our power consumption tests during photos retouching in the image editing application. Although Photoshop CS4 doesn’t always load all processor cores and video codecs on the contrary create pretty severe processor load, the correlation between the results of overclocked and non-overclocked processors remains the same.
And you shouldn’t be surprised with what you see. When the CPU frequency increases and the core voltage remains constant, the system power consumption grows linearly, and the constant of proportion in this case is relatively low. The time it takes the processor to complete its tasks also decreases linearly as the CPU frequency increases. However, since only the processor contributes to the system power consumption increase during overclocking, while other platform components do not change their power characteristics, the performance increases faster than the power consumption. The result in this case is quite logical: if the processor Vcore doesn’t change and remains at the nominal level as its frequency increases, overclocking ends up being beneficial in terms of power consumption minimization.