We decided to tweak the CPU core voltage and introduce a minor Vcore reduction to see if we could make another impact on power consumption. Experience tells us that a few percent voltage reduction typically doesn’t lead to stability issues. However, excessive undervolting can certainly be problematic, and insufficient voltage supply can be complex and tricky to identify. If you aren’t sure, we recommend staying close to the default voltage to avoid unneccessary issues.
MSI’s ControlCenter tells us that the default voltage for our test system is 0.95V (idle). CPU-Z confirms the setting and tells us that it’s effectively 0.944V.
We decided to adjust the voltage from 0.95V to 0.90V in the ControlCenter software.
The result was an effective CPU voltage of 0.888V at idle.
Peak Vcore at default auto settings.
Here's the peak Vcore at 0.9V manual setting.
We measured a decrease in system power at the reduced settings, but the impact was negligible at idle. At peak load, we had a decrease from 80W to 76W total system power.
There are still a few components left to optimize: the main memory and the hard drive. We tried removing one of the two DIMMs, but since DDR3 memory uses less power than DDR2, the impact was extremely small—doubly predictable, since we were running the DDR3 at 1,333 MT/s and default voltage. However, we have room to drop consumption versus the Western Digital VelociRaptor in our reference system, since it was never designed to be a low-power component.
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We received Toshiba’s newest 640GB 2.5” hard drive, the MK6465GSX, at about the same time we completed this review. Since its power consumption is among the lowest seen in today's hard drives, we decided to use it instead of a faster 3.5" desktop drive.
The 5,400 RPM Toshiba helped deliver additional power savings. System idle power went from 26W with the undervolted system on the 220W FSP power supply to as little as 23W. That put us under the 25W target for which we were aiming. The difference at peak load is only two watts, but we’re getting close to the accuracy limits of our measuring equipment at this point. The MX6465GSX is also available in 160, 250, 320, and 500 gigabyte capacities. A detailed review of the new 640GB drives will follow soon.
Of course, a solid state drive is also an option here, but the limited capacity would be an issue for most folks, and the increased cost would push the value of this build in the wrong direction. For that reason, a 2.5" mobile drive with more room for storage makes the best sense.
| System Hardware |
| Hardware |
Details |
| Motherboard (LGA 1156) |
MSI H57M-ED65 (Rev. 1.0)
Chipset: Intel H57, BIOS: 1.0B28 (04/01/20100) |
| CPU Intel |
Intel Core i5-661 (32nm, 3.33 GHz, 2 x 256KB L2 and 4MB L3 Cache, TDP 87W, Rev. B1) |
| RAM DDR3 (dual) |
2 x 2GB DDR3-1600 (Corsair CM3X2G1600C9DHX) |
| Graphics |
Intel HD Graphics
|
| Hard Drive I |
Western Digital VelociRaptor, 300GB (WD3000HLFS), 10,000 RPM, SATA 3 Gb/s, 16MB Cache |
| Hard Drive I |
Toshiba MK6465GSX, 640GB, 2.5," 5,400 RPM, SATA 3 Gb/s, 8MB Cache |
| Power Supply I |
PC Power & Cooling, Silencer 750EPS12V 750W |
| Power Supply II |
Fortron FSP220-60LE 220W |
| System Software & Drivers |
| Operating System |
Windows Vista Enterprise Version 6.0 x64
Service Pack 2 (Build 6000) |
| Drivers and Settings |
| Intel Chipset Drivers |
Chipset Installation Utility Ver. 9.1.1.1025 |
| Intel Storage Drivers |
Matrix Storage Drivers Ver. 8.8.0.1009 |
Results: Idle and Peak Power
We started off at 33W idle power, which is low but not revolutionary. We then exchanged the high-power PSU with a more efficient one.
The most important thing in this measurement is the fact that we aligned the PSU’s output to the expected system power consumption as much as possible. A 750W PSU running at only 40W load would be pretty inefficient. For this reason, the idle power decreased from 33W to only 26W. Even our small voltage decrease didn’t make much of a difference . The only other step that had an impact was the use of Toshiba’s 640GB 5,400 RPM hard drive instead of the high-performance WD VelociRaptor. Ultimately, we dropped from 33W to 23W with only two component changes. This is a 30% reduction in idle power.
Peak power doesn’t differ that much, as even the 750W Silencer power supply is operating at much more efficient levels. This is why its replacement doesn’t make as much of a difference under a heavy load. The voltage tweak, however, did make a difference of 4W. Another 2W could be saved through the more efficient hard drive.
Overall, the total impact on peak power is less significant than the change in idle power. This is where a desktop-class build will be significantly more power-hungry than a machine centering on Intel's Atom CPU. However, most desktops will spend little time using this much juice. In return, they also finish the same tasks in less time.
Once again, we ran our efficiency suite, which consists of several scripted benchmarks.
Since we keep tracking power in one-second intervals, we can calculate the average power used for the entire workload. The difference is significant considering that the performance does not change. All we're doing is modifying components and voltage settings in an effort to decrease power consumption.
The results on total power used for this test run are similar to the average readings.
The total runtime is one form of a performance result. As you can see, the results are very similar for the first three configurations. The last test run, which was conducted with the slower but more efficient Toshiba 2.5” hard drive, delivers less overall performance due to the decreased disk performance.
We divided the performance result by the power used to get our efficiency score. As expected, efficiency increases quite a bit.
Zoom
The efficiency diagram visualizes power consumption at every point of the benchmark run and also shows differences in runtime.
We expected that it would be hard to get the Core i5-661 system to run at only 25W idle power, but it turned out that the entire project was pretty easy to execute. Our test results show impressively that matching the power supply to your expected output (with some power reserves, of course) is imperative. Replacing the high-output 750W PC Power and Cooling PSU, which is a neat piece of hardware for a high-end gaming rig, with a low-power 220W PSU made the largest difference in our efforts to lower system power. Everything else is secondary. Voilà—26W reached with zero performance impact.
We tried running the system with only one DDR3 DIMM module instead of two, but found that the savings are below 1W. At the same time, this measure would have had a noticeable impact on performance. This also applies to the hard drive, but we were able to save an additional 2W to 3W there. Still, even if you only pick a suitable power supply and optimize component voltage, it's absolutely possible for anyone to recreate our 25W build—assuming that you go for the latest mainstream 32nm Intel hardware and a motherboard with the H55/H57 chipset. The voltage reduction reduced peak power, but had little impact on idle power.
And Now?
Let me come back to the question of why this is relevant. For power users, it really isn't. You'll probably go straight to a quad-core machine and not bother with power consumption questions. For average users, it becomes relevant if you want to go for a low noise system, or if you intend to pair high performance with the lowest possible acoustic footprint. This is typical of an HTPC, living room machine, or home server application. Keep in mind that a 3+ GHz Core i5 dual-core system is significantly faster than any other dual-core configurations around. It's finally possible to get strong performance at the power consumption levels of a dreadfully-slow Atom machine.
Intel’s Low Power Platform Means Higher Cost
However, there is a significant catch: you have to be aware that the new Intel platform is not a bargain. The processors are expensive, especially if you look at AMD’s pricing in comparison. Obviously, AMD has to stay aggressive on pricing to remain competitive from a performance perspective, but the result really makes you wonder. Do you really need to spend several hundred bucks on a Core i5 solution to reach the lowest power, or will an AMD solution at half the cost, but higher power consumption, be more suitable? We've made it clear that energy cost isn’t really an issue at this low level. If you want to go for the lowest power, for whatever reason, Clarkdale-based Core i5 processors paired with suitable components are unbeatable. They're just expensive relative to the competition, which is why we continue to recommend the i5-750 to enthusiasts at the $200-ish price point where you find the i5-661.
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