Overclocking and undervoltingIvy Bridge has the same overclocking mechanism as Sandy Bridge. Overclocking by the bus is very limited (around 5 to 7%) and only the K processors have a free multiplier, which is what is required for a good increase in clock.
On Ivy Bridge the maximum multiplier is up to x63 from 59 on Sandy Bridge, which gives a maximum clock of 6.3 GHz without overclocking the bus, which will only interest those who are adept at overclocking via LN2. The IGP also has a higher overclocking margin, which is now x60 instead of x57, giving a maximum of 3 GHz (steps of 50 MHz).
As with Sandy Bridge, it’s the Turbo multipliers that are modified for overclocking and the thermal envelope has to be increased at the same time to avoid seeing clocks drop back down in load to the base clock. These multipliers can now be modified in real time in Windows.
The memory has also received its lot of innovations. In addition to official support for DDR3-1600, Ivy Bridge now allows you to go up to DDR3-2667, as against DDR3-2133 on Sandy Bridge. In practice, ASUS for example has taken things further and offers up to a ratio of DDR3-3200.
We now have granularity in steps of 200 or 267 MHz, but strangely on its own DZ77GA-70K motherboard only the following ratio settings were accessible: DDR3-1067, 1333, 1600, 1867, 2133, 2400, 2667. ASUS however does make the 200 MHz steps available.
On the Intel motherboard we overclocked four processors cooled by a Noctua NH-U12P SE2 with a room temperature of 25°C (tests outside casing):
- Core i7-2600K (old, January 2011)
- Core i7-2700K (recent)
- Core i5-3570K
- Core i7-3770K
We started with our Sandy Bridges, on which we set the Vdrop on Low instead of High by default in the manual settings (except for the setting allowing us to obtain 0.96V). We limited ourselves to 1.42V on the sensor, in steps of 0.05V – for some time Intel hasn‘t really been giving information on the maximum voltage supported on its processors. At 32nm, you’re advised not to exceed 1.4V and at 22nm you'd expect the threshold to be even lower (1.3V?).
The Core i7-2600K is fairly reluctant when it comes to major clock increases, as you'd expect. For 3.5 GHz we used a voltage of 1.06V, then 1.21V for 4 GHz and 1.35V for 4.5 and 4.6 GHz. Although we went up to 1.42V, we weren’t able to stabilise it at 4.7 GHz. At 4.5 GHz the temperature of the cores was 67°C, compared to 51°C by default, an increase of 16°C.
The Core i7-2700K was more supple in spite of a similar undervolting with 1.06V at 3.5 GHz. Only 1.16V was required for 4 GHz, 1.31V for 4.5 / 4.6 GHz, 1.36V for 4.7 / 4.8 GHz and 1.42V for 4.9 GHz. At 4.5 GHz the temperature was 66°C against 51°C by default, which is an increase of 15°C.
The first Ivy Bridge tested, the i5-3570K supports undervolting with 0.96V at 3.5 GHz. We weren’t able to go any lower on the DZ77GA-70K motherboard. We managed 4 GHz at just 1.01V but we had to go up to 1.26V to clock 4.5 GHz and 1.36V to clock 4.6 GHz. At this clock, the temperature was 72°C against 56°C by default, which is an increase of 16°C.
Like the i5, the i7-3770K clocks 3.5 GHz at 0.96V. To clock up to 4 GHz however we had to increase the voltage to 1.06V and, as with the i5, it clocked 4.5 GHz at 1.26V. To get another 100 MHz we had to increase voltage by 0.05V and then another 0.05V to clock 4.7 GHz. At 4.5 GHz the temperature of the cores was 76°C, compared to 59°C by default, which is an increase of 17°C.
In terms of clocks, these first Ivy Bridges don’t seem to be all that powerful. Of course, overclocking isn’t an exact science and it’s difficult to generalise on such a small sample. Nevertheless our results seem to be in accord with the first tests from other people in possession of Ivy Bridge processors: while you can get close to and even reach 5 GHz with a recent Sandy Bridge, you have to aim at something more like 4.5 GHz with Ivy Bridge.
In comparison to energy consumption at the ATX12V at the base clock, we managed to stablise the processor at clocks of 3.5 GHz, 4.0 and 4.5 GHz with the following increases or decreases in energy consumption:
- i7-2600K: -26% / +9% / +64%
- i7-2700K: -26% / +0% / +50%
- i5-3570K: -29% / -14% / +61%
- i7-3770K: -30% / -9% / +61%
The current Ivy Bridges seem at ease with a clock of around 4 GHz as this overclocking can be obtained at lower energy consumption than the initial level. At 4.5 GHz, we are however too close to their maximum and the increase in voltage leads to a significant increase in energy consumption.