Lesson 04 - Overclocking from 3.2GHz to 3.7GHz
In this lesson we will overclock an Intel Core i7 920 CPU from 3.2GHz through 3.7GHz. We will also show overclocking the memory and how to use voltage settings to improve the stability of the CPU overclock.
Overclocking to 3.3GHz
We're back in the BIOS and we're going to go for 3.3GHz. To get there we need to set the base clock to 165MHz. 165 x 20 gives us 3300 or 3.3GHz. When we made that change the RAM, Uncore and QPI automatically updated. Let's take a look. The RAM changed to 1322MHz. This is below its rated speed of 1333MHz so it's fine. The Uncore is slightly more than double the speed of the RAM which is what we want and the QPI is on the lowest setting available. So we'll press F10 and Ok to save and exit. The CPU is running at 3.3GHz and the memory at 1322MHz.
The temperature at idle, according to RealTemp, is 58c. I'll run Prime95 on the large FFts setting to get the load temp. The load temp is 85c after 14 minutes. Last, I'll get the CPU score. CPU score in 3dmark06 is 6216 . The overclock is stable.
I've taken notes of all the results. Let's restart and go into the BIOS.
Overclocking to 3.4GHz
Let's try 3.4GHz. A base clock of 170 x a multiplier of 20 gives us 3400 or 3.4GHz. Once again the RAM, Uncore and QPI changed automatically. The RAM is now set faster than its rated speed of 1333MHz. I'm going to lower the RAM speed to 1023GHz. This will underclock the RAM well below its rated speed, or 1333MHz ,and rule out the RAM as being the cause of any instability. I'll change the Uncore frequency to 2045 which is twice the speed of the RAM and the QPI is fine at 6135. I'll write these settings down, press F10 and Enter to save and exit.
Idle temp is 57c. Load temp is 84 at 15 minutes. CPU Score in 3dmark06 is 6347 and the overclock is stable.
Overclocking to 3.5GHz
We're back in the BIOS so let's try 3.5GHz. A base clock of 175 x a multiplier of 20 gives us 3500 or 3.5GHz. Once again the RAM, Uncore and QPI changed automatically. The RAM changed to 1053MHz. The next highest available setting is 1403MHz which is higher than the memory specs so we'll leave it at 1053MHz. The Uncore is set to 2105MHz which is double the RAM speed and the QPI is set to 6316 which is the lowest possible setting. I'll write these settings down, press F10 and Enter to save and exit.
Let's check out RealTemp. Idle temp is 58c. Load temp is 86c at 13minutes. CPU Score in 3dmark06 is 6553 and the overclock is stable.
Overclocking the RAM
Before we try 3.6GHz I'd like to see if the RAM will run faster than its rated speed. The next highest setting is 1403MHz. The Uncore automatically updated to 2807MHz which is twice the speed of the RAM. This will be overclocking the RAM which could introduce instability so these are the only changes we will make. I'll note the change, press F10 and Enter to save and exit.
We didn't change the CPU overclock so the idle temperature shouldn't change. In Prime95 we're going to choose the Blend setting which will stress the RAM. This is a different test so the load temperatures may be a little different. It's been running for 14 minutes without an error showing up, the system freezing or restarting so the RAM appears stable. However, Prime95 is mostly intended to stress the CPU, not the RAM.
A better test we can run to stress the RAM and make sure it's stable is called BurnInTest. You can download it from www.passmark.com. We'll click Download. There is a standard and a pro version and 32 and 64bit versions of each. We'll download the Pro, 32bit version. The Pro version has the most options for testing. There is a 30 day trial before you buy which is plenty of time to test one system. Just run the exe once it downloads and install it. We've already installed it on this system so I'll launch it.
To test the RAM we'll click this down arrow and choose RAM. If you've installed the Standard version you can get to the same test by clicking Quick Tests and RAM. Click the green arrow and OK to start the test. If there are any errors they will be shown here. BurnInTest has a few CPU tests we can use, in addition to Prime95, to test for stability. The test passed so the RAM is stable at 1403MHz. If the test failed we could either increase the voltage going to the RAM or increase the RAM's timings. We will show how to do this in Lesson 5.
Overclocking to 3.6GHz
Next we'll try to get the CPU to 3.6GHz. A base clock of 180 x a multiplier of 20 gives us 3600 or 3.6GHz. Once again the RAM, Uncore and QPI changed automatically. The RAM changed to 1443MHz. Since we are trying a higher CPU overclock I'll change that to 1083MHz to rule out the RAM as being a cause of any instability. I'll change the Uncore to 2165MHz which is twice the RAM speed and the QPI is at its lowest possible setting. I'll make note of the settings, press F10 and Enter to save and exit.
Let's check RealTemp. The idle temp is 57c. Load temp is 87c at 13 minutes. CPU Score in 3dmark06 is 6724 and the overclock is stable.
Overclocking to 3.7GHz
Let's try to get the CPU to 3.7GHz. A base clock of 185 x a multiplier of 20 gives us 3700 or 3.7GHz. Once again the RAM, Uncore and QPI changed automatically. The RAM changed to 1113MHz which is fine. The Uncore is 2226MHz which is twice the speed of the RAM and the QPI is at its lowest possible setting. I'll make note of the settings, press F10 and Enter to save and exit.
Let's check RealTemp. The idle temp is 57c. I'll start Prime95 on the large FFts setting. The computer just restarted itself. Prime 95 had been running for 1 minute and the temperature was in the low 80s. The computer restarting is a definite sign of an unstable overclock. Since every system is different, your computer may become unstable at a lower or higher overclock.
Increasing the CPU Core Voltage
Let's go into the BIOS. In order to stabilize the overclock we need to increase the voltage to the CPU cores using the CPU Voltage setting. We may also need to increase the voltage to the CPU PLL and QPI. However, we want to be methodical and only change one setting at a time. I'm going to increase the CPU Voltage to 1.225 volts and then check for stability.
I"ll start up RealTemp to keep an eye on the temperatures. The idle temp is around 60c. I'll start Prime95 on the large FFts setting just like before. The temperatures at load are now going over 90c which is dangerous over long periods. When you increase the voltage the temperatures will increase much more quickly than with frequency increases. The computer restarted again. Prime95 had been running for about 4 minutes and the temperatures were in the low 90s.
Increasing the QPI Voltage
We need more voltage to get the system stable at 3.7GHz. I'm going to increase the QPI voltage to 1.225 volts as well and then test for stability.
I'll run the same test in Prime95. It restarted again. Prime95 was running for about 6 minutes and the temps were around 92c.
Increasing the CPU PLL Voltage
Next, I'll increase the CPU PLL to 1.88 volts and test for stability. I'll run the same large FFts test in Prime95. The system restarted again.
Further increasing the CPU Core Voltage
I'm going to increase the CPU Voltage further to 1.25 volts. The motherboard is showing this setting in yellow meaning caution. If I increase it further it eventually changes to red meaning don't go there. I'll set it to 1.25 volts and test again. I'll open up RealTemp and the idle temperatures are now 62c. I'll run the large FFts test in Prime95. The load temps are reaching 97C and the individual core are spiking over 100c. Prime95 has been running for almost 20 minutes though, which is a good sign of a stable overclock. I'm going to close Prime95 and open BurnInTest. I'm going to use one of its CPU tests, the CPU coverage, for more verification of a stable overclock. It passed. I'll close down BurnInTest and I'll run 3dmark06 for more confirmation of a stable overclock and to get the CPU score. The CPU score is 6861.
The CPU is stable at 3.7GHz
The system is stable at 3.7GHz with the voltage increases. However, these voltage increases have taken the CPU temperatures above the recommended levels.
In the next lesson we will replace the stock Intel CPU cooler with a 3rd party cooler to improve the CPU's cooling. We will then attempt to overclock the CPU to 3.8GHz.