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CPU Clock Speeds
Before we start, we should note that our i5-2500K processor sample (or the DH67BL board) was a little off in that the bus speed operated at lower than normal levels. It should be 100 MHz, but we caught it running at 89 MHz when idle, and 97 MHz with all four cores on load with TurboBoost enabled.
CPU-Z screenshot: i5-2500K at idle.
CPU-Z screenshot: i5-2500K at full load.
As LGA1156 quad cores lack integrated graphics, we pit the i5-2500K and its HD 3000 graphics up against the Core i5-661. It's an 87W dual core processor with a slightly higher clock speed, Hyper-Threading, and the previously top-end GMA HD graphics clocked at 900 MHz. To make things a little more fair we tested the i5-2500K at stock settings and with two cores disabled. A Radeon HD 5450 was thrown into the mix to compare the onboard graphics to a proper entry level discrete card.
As a platform, the i5-2500K paired with the DH67BL was very efficient, boasting a small improvement over the i5-661 in power consumption when idle and an almost 10W advantage when playing x264 video. With two cores disabled, only load power was truly effected, but this probably isn't indicative of how much juice a proper dual core Sandy Bridge will actually use.
At stock settings, adding FurMark to a Prime95 load on the i5-2500K induced an 11W jump, but when two of the cores were disabled, this difference increased to 18W. This is evidence that the "power sharing" GPU feature is actually working. With two cores inactive, the extra thermal headroom appears to allow the GPU to safely clock itself faster. The HD 5450 added about 6W to the total energy usage.
Our CPU/VRM measurements were taken from the
AUX12V connector with the help of a pair of digital multimeters and an in-line
0.01 ohm shunt resistor and represents the approximate draw of the +12V line by the processor including inefficiencies lost to the VRMs. Again we see the i5-2500K's GPU using more power when two of the CPU's cores were disabled, even more than the Radeon HD 5450.
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