Sunday March 14th, 2010By: CyrIng

The purpose of this paper is to get the best of the Intel Core i7 revision 920/C0 by overclockling its frequency with the benefits of less power comsumption and thereforeless heat dissispation and less noise.

The CPU frequency is set during system boot by multiplying the Base Clock with the CPU Ratio.

CPU (Mhz)….=….BCLK (Mhz)….x….Ratio

While the Core i7-965 Extreme has an unlocked ratio, the revision 920 of the processor is locked to a range of ratios from 12 to 21 .

2666 Mhz….=….133.33 Mhz….x….20

2800 Mhz….=….133.33 Mhz….x….21……+1 bump

Although, and thanks to the Turbo mode technology, a ratio of 22 can be permanently locked when one and only one of the four cores is activated. See BIOS [*Active Processor Cores]

2933 Mhz….=….133.33 Mhz….x….22……+2 bump

The alternative is to play with the base clock ranging from 133 Mhz up to 200 Mhz and beyond.

However you will notice that increasing the CPU frequency implies an increase of the voltage required by the processor, and thus a raise of its heat dissipation.

For instance, setting in the BIOS of the Rampage II GENE motherboard a base clock above 152 Mhz automatically generates a voltage of 1.24V, even when the system idles.

( check our benchmark )

1824 Mhz….=….152 Mhz….x….12@ 1.24V

3040 Mhz….=….152 Mhz….x….20@ 1.25V

As shown bellow, the BIOS trick is to set the parameter CPU Voltage Control to the value [Relative Offset].

Using BIOS release 1307, we have then been able to reach a base clock frequency of 175 Mhz with a 1.05V voltage when system idles and arround 1.25 V during load.

2100 Mhz….=….175 Mhz….x….12@ 1.05V

3675 Mhz….=….175 Mhz….x….21@ 1.25V

3850 Mhz….=….175 Mhz….x….22@ 1.25V

You might also notice that the IOH does not automatically adjust to its minimum voltage and remains arround 1.17V.

Constrain to the value [1.11341] corrects the proper voltage and thereby helps to decrease the heat of the Northbridge chip up to 58°C

Test setup : Cube WorkStation

  • MB = ASUS Rampage II GENE [BIOS:1033]
  • CPU = Intel Core i7 920 rev C0
  • HS = Corsair H50 watercooling kit
  • RAM = Corsair DDRIII Dominator
  • Fans = 1 x Noctua 120mm (front) ;1 x Corsair 120mm (WC’s pump @ front) ;2 x LianLi 120mm ( X58 and GPU ) ;1 x Noctua 90mm (Rear)
CyrIng 1239

Base clock frequency set to 160 Mhz : as fast as the Core i7-965

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Enable Load-Line Calibration and CPU Voltage Control to Relative Offset

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Optionnaly, enhance the cpu clocking ability by disabling

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Enable all CPU power functions, especially C-State to C6

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Adjust the DDR memory timings with the lowest latency found into SPD registers

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Leave the other timings to Auto

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The H50 stays quiet with an average fan speed at 1237 rpm . The two 120mm front fans running arround 1000 rpm

CyrIng Load CPU-Tweaker

Results when doing load testing

CyrIng Idle CPU-Tweaker

Results when system idles


CPU core temperature during load testing