Energy-efficient Core i5-2400S turned out to be not as fast as we had expected it to be, considering that it is a Sandy Bridge product. For the sake of lower heat dissipation, its clock frequency has been significantly reduced, so there is nothing to be surprised about here. It is a different question, whether it was worth it. Is a slower Sandy Bridge processor a real energy-efficient CPU? Power consumption tests will help us to answer this question.
The graphs below show the full power draw of the computer (without the monitor) measured after the power supply. It is the total of the power consumption of all the system components. The PSU's efficiency is not taken into account. The CPUs are loaded by running the 64-bit LinX 0.6.4 utility. Graphics cores were loaded using FurMark 1.8.2 utility. Moreover, we enabled C1E and Enhanced Intel SpeedStep power-saving technologies to ensure that computer power draw in idle mode is measured correctly.
In idle mode there is no real difference between energy-efficient and regular processors. It is quite logical as in this case all power-saving technologies kick in and the clock frequencies of all Sandy Bridge processors drop to 1.6 GHz. However, Sandy Bridge platform consumes considerably less power in this mode than an LGA1156 platform: new processors distribute power better in idle mode by disconnecting the idling units and lowering the graphics core frequency, too.
However, when the computational cores are loaded to the full extent, we can clearly see the power advantage of Core i5-2400S processor. Lower clock speed and core voltage work their magic and the system with a Core i5-2400S inside needs 13 W less power than the system with a regular Core i5-2400. Of course, it is nothing like 30 W of difference in thermal characteristics between the two new processors, but still it is tangible.
By the way, speaking specifically about the CPU power consumption, we can offer you the following data from the System Agent for your reference:
In other words, 95 or 65 W are not even close to what we see. The calculated TDP is obviously declared with a substantial reserve, so even a regular Core i5-2400 consumes less than 65 W under heavy load, and Core i5-2400S can actually be assigned the lowest 45 W TDP just fine.
However, we haven’t yet checked out graphics load. Let’s see what happens when the integrated graphics core is busy processing 3D graphics.
Core i5-2400S and Core i5-2400 demonstrate almost the same power consumption in this test. So, it looks like the S-processors can only be called energy-efficient in relation to their computational cores, but not the integrated graphics. Which is exactly what we could expect taking into account that Intel HD Graphics 2000 core is the same in a regular and energy-efficient CPUs. By the way, both graphics cores, in Core i5-2400S and Core i5-2400, use the same GU voltage setting.
The results obtained under complex load involving all CPU resources are quite expected:
Core i5-2400S based system needs less power due to lower power consumption of the computational cores. Moreover, total maximum power consumption of the system including a mainboard with the CPU and memory, an SSD and a boxed CPU cooler fits within 70 W if we have an S-series processor, and within 80 W if we have a regular Sandy Bridge CPU. These numbers speak for themselves: the new LGA1155 platform poses as a great candidate for a compact and quiet computer system.
Another type of complex workload is HD video playback. They managed to almost completely unload the computational cores due to a special hardware video coder in the new Sandy Bridge processors.
Moreover, the LGA1155 system is overall surprisingly energy-efficient. It is not without reason that Intel claims Sandy Bridge to be a great choice for HTPC.
Power consumption during HD video content playback is only 6 W higher than power consumption in idle mode on any Sandy Bridge modification.