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Overclocking Intel Core i7 processors
Preface
Overclocking the Core i7 series of processors is not that different from what we know from overclocking of the Core 2 processors.
With Core i7 processors, all frequencies originate in a Base Clock (BCLK) with a default frequency of 133.33 MHz. From this base frequency, all other frequencies are derived by applying various multipliers.
Note that the available BIOS settings/options vary among the ASUS 1366 motherboards.
Overclocking
Easiest to overclock is the Core i7 965 Extreme Edition, due to its unlocked CPU multiplier. To overclock the CPU to e.g. 4 GHz, we simply need to raise the CPU multiplier (CPU Ratio) from default 24 (3.2 GHz) to 30 (4.0 GHz), while keeping BCLK at the default frequency, 133.33 MHz.
To achieve the same overclock (4 GHz) on the models Core i7 920 and Core i7 940, the Base Clock frequency has to be increased, since their CPU multipliers are upwards locked at their highest option, 21 for i7 920 and 23 for i7 940. The change of BCLK means that all other clock frequencies are influenced (memory, Uncore and QPI).
As an example, overclocking a Core i7 920 to 4 GHz, using the default CPU multiplier (20), would need an increase of BCLK from default 133 (133.33) MHz to 200 MHz (4000 / 20 = 200 MHz). That is a serious overclock that will put stress on the processor chip, which besides the CPU cores also contains the IMC (Integrated Memory Controller), the Uncore (L3 cache) and QPI (Quick Path Interconnect). The memory frequency, the Uncore (UCLK) frequency and the QPI frequency have to be adjusted accordingly.
Core i7 Processors – Frequency relations
BCLK (Base Clock)
Range: 100 – 500
Default: 133.33 MHz
Stability common up to BCLK ~180.
Max out @ BCLK between 180 and 220.
CPU Frequency =
BCLK x CPU Multiplier
i7 920 – 2.66, i7 940 – 2.93, i7 965 – 3.20,
i7 950 – 3.06, i7 975 – 3.33 GHz
DRAM Frequency =
BCLK x Memory Multiplier
Memory Multipliers: 6, 8, 10, 12, 14, 16
UCLK Frequency =
BCLK x Uncore Multiplier
e 2 x DRAM Frequency and < QPI Frequency
QPI Frequency =
BCLK x QPI Multiplier
> Uncore Frequency
Multipliers / Frequencies @ BCLK = 133 MHz
Processor
Model
CPU Ratio
(Multiplier)
Memory
Multiplier
UCLK (Uncore)
Multiplier
QPI
Multiplier
Core i7 920
2.67 GHz
12 – 21
Default 20
6, 8, 10,
12, 14, 16
(DDR3-800)
(DDR3-1066)
(…………….)
(DDR3-2133)
e 2 x Memory Multiplier
12, 13, 14, 15, ….., 26
(1600MHz)
(1733MHz)
(………….)
(3466MHz)
18, 22, 24
(36, 44, 48)
(4800 MHz)
(5866 MHz)
(6400 MHz)
Core i7 940
2.93 GHz
12 – 23
Default 22
Core i7 965
Extreme Ed
3.20 GHz
12 – unlocked
Default 24
ASUS has chosen to use the resulting frequencies instead of the multipliers in BIOS.
The available options for DRAM Frequency depend on the BCLK.
The available options for UCLK depend on the BCLK and the Memory multiplier.
The available options for QPI depend on the BCLK and the UCLK.
Turbo Mode Tech (enabled by default)
When “Turbo Mode Tech” is enabled, the CPU multiplier may automatically increase with 1 or 2 for i7 920/940 and with up to 4 for i7 965 Extreme. The highest CPU Ratio is achieved when only 1 core is active.
CPU Ratio has to be set to [Auto] to allow this function.
Strategies for overclocking
To simplify a stable overclocking, different strategies can be used. I’ll here focus on the Core i7 models i7 920/940. Core i7 965 Extreme Edition is simpler to overclock, due to the unlocked CPU multiplier, which eliminates the need to raise the Base Clock (BCLK).
Core i7 920:
A good starting point could be to calculate which BCLK you would need to achieve your desired CPU speed. Let’s say that you would like a CPU speed of 3.4 GHz. The needed BCLK then is: 3500 / 20 = 170 (using CPU Ratio 20, which is the default CPU multiplier for Core i7 920).
Let’s say that you want to use DDR3-1333 MHz memory. Determine the memory multiplier as 1333 / BCLK (1333 / 170 = 7.8) Use the nearest memory multiplier, which is 8. The nearest selectable option for DRAM Frequency will then be BCLK x 8 (170 x 8 = 1360). Select DRAM Frequency [DDR3-1360].
The Uncore multiplier should be greater than, or equal to, 2 x the memory multiplier: 2 x 8 = 16.
Uncore Frequency is BCLK x Uncore multiplier (170 x 16 = 2720). Select UCLK Frequency [2720MHz]. The setting can also be left at [Auto].
QPI multiplier should be higher than the Uncore multiplier (Uncore : QPI = 8 : 9. The lowest QPI multiplier is 18 (36), which mean a QPI frequency of (170 x 18 = 3060), which is higher than the Uncore Frequency. Select QPI Frequency [6120MHz] (36 x 170). The setting can also be left at [Auto].
Next step is to relax the CPU Ratio to 12 (lowest multiplier) and run Memtest86+ v2.11 (or later) to verify the stability for memory and QPI (without any risk for limitations due to the CPU speed).
If Memtest86+ runs error free, set CPU ratio to 20, 21 or [Auto] (Auto means default 20, but with Turbo Mode normally 21).
Finally, running Orthos or Prime95 for a total of 8 virtual cores, the PC has to be stable for at least overnight.
Manual configurations (parameters for Asus P6T Deluxe)
Ai Tweaker menu
Manual: Allows you to individually set overclocking parameters
Auto: Loads the standard settings for the system
D.O.C.P.: Overclocks DRAM Frequency by adjusting the BCLK frequency
X.M.P.: If you install memory modules supporting eXtreme Memory Profile (X.M.P.) Technology, choose this item to set the profile(s) supported by your memory modules for optimizing the system performance
CPU Voltage [1.2V – 1.35V] should be optimized (see below)
CPU PLL Voltage [Auto] or [1.80V – 1.96V]
QPI/DRAM Core Voltage [1.2V – 1.35V] important for stability (QPI / Uncore)
DRAM Bus Voltage [max 1.64V] Intel states, that DRAM voltage beyond 1.65V may permanently damage the processor.
QPI/DRAM Core Voltage must be within 0.5V of DRAM Bus Voltage.
The other voltages may be left at default (Auto).
BCLK Frequency [XXX] (default 133 MHz)
DRAM Frequency [DDR3-XXXX]
PCIE Frequency [100] (locks the PCIE frequency)
Voltage optimization
At least CPU Voltage and DRAM Bus Voltage should be set manually.
When you are satisfied with your overclocking, I recommend optimizing CPU Voltage and DRAM Bus Voltage, which means finding the lowest possible voltage where 100% stability is achieved for at least a run overnight.
Start with optimizing the memory voltage by lowering the DRAM Bus Voltage by 1-2 notch(es) at a time, until Memtest86+ shows errors within 10 minutes – then increase by 1 notch and test again. In the end, not a single error is allowed for a run overnight.
Use Orthos/Prime95, as described for memory voltage, to find the lowest possible CPU Voltage that allows the PC to run error free for at least overnight.
Overclockings for Core i7 920 / Core i7 940
Base Clock
(BCLK)
MHz
Memory
Multiplier
DRAM Freq. MHz
Uncore
Multiplier
UCLK Freq. MHz
QPI
Multiplier
QPI Freq. MHz
CPU i7 920
Multiplier
Freq. GHz
CPU i7 940
Multiplier
Freq. GHz
133.33
6 <> DDR3-800
12 <> 1600
18 (36) <> 4800
21 <> 2.80
23 <> 3.06
133.33
8 <> DDR3-1066
16 <> 2133
18 (36) <> 4800
21 <> 2.80
23 <> 3.06
133.33
10 <> DDR3-1333
20 <> 2666
22 (44) <> 5866
21 <> 2.80
23 <> 3.06
133.33
12 <> DDR3-1600
24 <> 3200
24 (48) <> 6400
21 <> 2.80
23 <> 3.06
150
10 <> DDR3-1500
20 <> 3000
22 (44) <> 6000
21 <> 3.15
23 <> 3.45
160
10 <> DDR3-1600
20 <> 3200
22 (44) <> 7040
21 <> 3.36
23 <> 3.68
167
8 <> DDR3-1336
16 <> 2672
18 (36) <> 6012
21 <> 3.50
23 <> 3.84
180
8 <> DDR3-1440
16 <> 2880
18 (36) <> 6480
21 <> 3.78
22 <> 3.96
185
8 <> DDR3-1480
16 <> 2960
18 (36) <> 6660
21 <> 3.88
22 <> 4.07
190
8 <> DDR3-1520
16 <> 3040
18 (36) <> 6840
21 <> 3.99
21 <> 3.99
195
8 <> DDR3-1560
16 <> 3120
18 (36) <> 7020
21 <> 4.09
21 <> 4.09
200
6 <> DDR3-1200
12 <> 2400
18 (36) <> 7200
20 <> 4.00
20 <> 4.00
200
8 <> DDR3-1600
16 <> 3200
18 (36) <> 7200
20 <> 4.00
20 <> 4.00
(180)
10 <> DDR3-1800
20 <> 3600
22 (44) <> 7920
21 <> 3.78
22 <> 3.96
(200)
10 <> DDR3-2000
20 <> 4000
22 (44) <> 8800
20 <> 4.00
20 <> 4.00
The CPU Multiplier is above set manually. Setting the CPU Multiplier to [Auto] with Turbo Mode Tech enabled (default) would normally mean a CPU multiplier of 21 for i7 920 and 23 for i7 940.
Note that there is no “guarantee” that the processor is able to run above 3.8 GHz. If adjusting CPU Voltage and/or CPU PLL Voltage doesn’t help, the CPU Multiplier (or the BCLK) can be lowered.
Rules and relations:
BCLK (Base Clock – default 133.33 MHz, range: 100-500)
CPU Frequency = BCLK x CPU Multiplier (CPU Ratio)
DRAM Frequency = BCLK x Memory Multiplier
UCLK Frequency = BCLK x Uncore Multiplier (Options: 1600-5600 MHz)
QPI Frequency = BCLK x QPI Multiplier (Options: 4800/5866/6400 MHz @ BCLK 133 MHz)
Uncore Multiplier (frequency) e 2 x Memory Multiplier (frequency)
Uncore Multiplier (frequency) : QPI Multiplier (frequency) ~ 8 : 9 for best stability
The above overclocking settings that best fulfill all the rules are:
