Efficiency Explored: What's The Perfect Clock Rate For Your Core i5?

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OC Settings And Clock Speed Table

The table below lists all clock speeds and settings that we used for this article. Please note that we had to switch off the Turbo Boost feature above 3.2 GHz, as the resulting maximum clock speed would have exceeded the highest reliable speed of roughly 4.2 GHz. Here is an overview of the resulting clock speeds realized when you increase the system clock without modifying the base multiplier (the first column is with a 20x multiplier), but with Turbo Boost enabled (columns with multiplier 21x and 24x):

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Target Clock Speeds Core i5 Overclocking Default Clock Speed at 20x Max. Turbo Boost Speed with 3 or 4 Active Cores (Multiplier+1) Max. Turbo Boost Speed with 1 or 2 Active Cores (Multiplier+4)
133 MHz BCLK 2,666 MHz (20x multipler) 2,800 MHz (21x multiplier) 3,200 MHz (24x multiplier)
150 MHz BCLK 3,000 MHz (20x multiplier) 3,150 MHz (21x multiplier) 3,600 MHz (24x multiplier)
160 MHz BCLK 3,200 MHz (20x multiplier) 3,360 MHz (21x multiplier) 3,840 MHz (24x multiplier)*
170 MHz BCLK 3,400 MHz (20x multiplier) 3,570 MHz (21x multiplier)* 4,080 MHz (24x multiplier)*
180 MHz BCLK 3,600 MHz (20x multiplier) 3,780 MHz (21x multiplier)* 4,320 MHz (24x multiplier)*

(*) These settings were unstable without application of additional processor core voltage, which we avoided.

Regardless of possible margins in the thermal envelope of the processor, our Core i5-750 did not operate higher than about 3.7 GHz without a voltage increase. As a result, we found that a 160 MHz base clock was the maximum stable setting we could use with Turbo Boost enabled and without increasing voltage.

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Certainly, you can increase the processor voltage in an effort to move default and Turbo Boost clock speeds further up, but this would also result in decreased efficiency in all operating states. Hence, a 160 MHz BCLK with a 3.2 GHz nominal speed and a Turbo Boost speed of 3.36 GHz for three or four cores and 3.8 GHz for one or two cores was the maximum here.

Clock Speed Table

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Core i5-750 3,000 MHz 3,200 MHz 3,400 MHz
Base Frequency 150 MHz 160 MHz 170 MHz
Turbo Boost Yes Yes No
System Idle Power 71W 71W 72W
SystemPeak Power 160W 164W 168W
BIOS Vcore 1.213V 1.213V 1.213V
CPU-Z VT idle 1.224V 1.224V 1.224V
CPU-Z VT load 1.176V 1.176V 1.176V
CPU VTT 1.101V 1.101V 1.101V
PCH 1.81V 1.81V 1.81V
RAM 1.51V 1.51V 1.51V
Fritz Chess Benchmark 9,167 9,642 9,981
Stable? yes yes yes
Swipe to scroll horizontally
Core i5-750 3,600 MHz 3,800 MHz 4,000 MHz 4,200 MHz
Base Frequency 180 MHz 190 MHz 200 MHz 210 MHz
Turbo No No No C-states off
System Idle Power 73W 75W 79W 122W
SystemPeak Power 175W 195W 245W 265W
BIOS Vcore 1.251V 1.32V 1.45V 1.52V
CPU-Z VT idle 1.256V 1.328V 1.448V 1.512V
CPU-Z VT load 1.208V 1.272V 1.384V 1.44V
CPU VTT 1.101V 1.149V 1.25V 1.303V
PCH 1.81V 1.85V 1.9V 1.9V
RAM 1.51V 1.51V 1.51V 1.51V
Fritz Chess Benchmark 10,405 11,008 11,501 12,157
Stable? yes yes yes yes