Intel Core i3-540
Besides LGA775 we also included Intel processors designed in other form-factors. Namely, we couldn’t leave out relatively new solutions from Clarkdale family designed for LGA1156 platforms. The primary argument in favor of including them into this test session was the fact that one of the two semiconductor dies used in these processors is manufactured with the today’s most advanced 32 nm technological process. This die is in fact a combination of two computational cores. The integrated memory controller together with the built-in graphics core is inside the second die of the Clarkdale processor, which is manufactured with 45 nm process. We have already said that this configuration composed of two semiconductor dies within the same processor packaging doesn’t perform its best. Now let’s see what is going on with the power consumption of a CPU like that, when we overclock it to different frequencies.
For our tests we took Core i3-540. This is a mainstream Clarkdale model. On the one hand, it supports Hyper-Threading technology, on the other – doesn’t support Turbo Mode, which is otherwise not very handy for overclocking. The nominal clock frequency of this processor is 3.07 GHz. It has 256 KB of L2 cache per each of the two cores, and a 4 MB shared L3 cache.
32 nm production technology allowed using pretty low core voltage for Core i3-540 CPU. Our processor, for instance, required only 1.125 V of power. However, processor North Bridge that is located inside the second 45 nm die uses its own voltage regulator circuitry and its own voltage of 1.1 V for our processor. In this case the total calculated TDP for Core i3-540 processor is set at 73 W, which means that despite the finest manufacturing process, Intel didn’t really make any breakthroughs in terms of improving their processors energy-efficiency. In fact, 73 W is even more than the TDP of dual-core LGA775 processors based on 45 nm dies and priced in the same range. However, our test session revealed a completely different picture. A Core i3-540 based system with the CPU loaded to its fullest extent consumed only 86 W of power in nominal mode, which is lower than the power consumption of an Intel Core 2 Duo E7600 based system. It must be a significantly simpler chipset used in LGA1156 systems that contributed to this result, as now it only consists of the South Bridge, since all the functions of the North Bridge have been transferred over to the processor.
The clock frequency of LGA1156 processors is derived from the base clock generator frequency (133 MHz in nominal mode) times the multiplier preset and locked at a certain value for each particular processor model. Therefore, we overclocked our Core i3-540 processor by raising the base clock. I have to say that 32 nm Clarkdale behaved quite unexpectedly during our overclocking experiments. We managed to hit only 3.2 GHz maximum without touching the processor core voltage. After that we could only continue to overclock our CPU if we gradually increased its Vcore. And in order to get our Core i3-540 to work stably at 4.2 GHz we also had to raise the voltage of the integrated North Bridge. The table below shows all system settings, at which we measured the power consumption:
All other voltages not mentioned in the table above were left at their default values.
So, let’s take a look at the total power consumption of our Core i3-540 based system during overclocking:
I have to say that the graph looks quite unusual. There is no plateau phase and no dramatic increase in the end. Since we had to resort to voltage adjustment already in the second overclocking increment, all significant power consumption peaks have been distributed all over the graph. Nevertheless, 37% clock frequency increase during Core i3-540 overclocking to 4.2 GHz produces a tangible 50 W growth of the total power consumption. We have seen almost the same gain during overclocking of the dual-core Core 2 Duo E7600 and Phenom II X2 555 processors.
The second graph has a few more surprises for us. It shows the changes in currents along the major mainboard power lines.
First, I would like to remind you that LGA1156 processors are powered not only via the 12 V line. Only the CPU’s computational cores are connected to it. The second processor core that contains the memory controller is fed via 12 V power line connected to the 24-pin power connector on the board. Therefore, the current going through these two power lines increases substantially during CPU overclocking. Moreover, it is especially interesting that in a number of cases, for example when the LGA1156 CPU works in its nominal mode, processor power line is not bearing the maximum load. This is a unique feature of all Intel systems equipped with Clarkdale processors. Unfortunately, since LGA1156 systems use a “distributed” voltage regulator, we can’t give a definite answer about the processor power consumption at this point. Nevertheless, even a quick glance at the graph lets us conclude that when we overclock our Core i3-540 from 3.07 to 4.2 GHz, its power consumption more than doubles.