Lesson 05 - Overclocking the CPU to 3.8GHz and beyond
First we will show how to find the maximum stable frequency on a Black Edition CPU using the CPU multiplier to raise the frequency. Then we will show how to find the maximum stable frequency on a non-Black Edition CPU using only reference clock increases to raise the CPU frequency.
Overclocking a Black Edition CPU
We'll press F12 and load the default settings we saved in Lesson 3. If we go into the MIT we can see that all of the overclocking related settings are at manual with their default speeds. To overclock this Black Edition CPU we need to increase the CPU multiplier. The reference clock being at 200MHz times the CPU multiplier of 16.5 gives use a CPU frequency of 3300MHz which is a 100MHz increase over the stock setting. You then save and exit the BIOS and go into Windows. Open Core Temp to keep an eye on the CPU temperature and run Prime95 on the Small FFT's test. Let it run for at least 20 minutes. You can also use the CPU Coverage test in BurnInTest to test for stability. Run them at the same time for a really good test. If the system is stable, reboot, come back into the BIOS and raise the multiplier another 100MHz and test in Prime95 and or CPU Coverage again. Continue to increase the multiplier until Prime95 or CPU Coverages fails with an error or if the system freezes, blue screens or reboots. Your last stable setting will be your CPU's maximum stable speed at stock voltage. You need to make a note of this speed and that it is with the stock voltage. My CPU's stock voltage is 1.4V and the highest stable frequency at stock voltage is 3.7GHz. Once you've found your CPU's maximum stable frequency at stock voltage you can go into the BIOS and increase the CPU voltage by .025V and try the next highest frequency again. If the system is stable write down the frequency and the voltage needed to make the system stable. If it isn't stable, raise the CPU voltage .025V at a time until the system is stable. Continue raising the frequency and increasing the voltage as needed to make the system stable at each new frequency. In my case the maximum stable frequency is 3.8GHz. I had to increase the CPU Voltage to 1.45V to get the CPU stable at 3.8GHz. Remember to keep an eye on the CPU temperature, using Core Temp, especially when you raise the CPU voltage above the stock setting.
Using Reference Clock Increases to Fine Tune the Overclock
With a Black Edition CPU multiplier increases are the main way to overclock the CPU. However you can use reference clock increases to fine tune the overclock. Using half steps of the CPU multiplier with the reference clock set to 200MHz gives you 100MHz increases in the CPU Frequency. If you increase the reference clock from it's stock value of 200MHz to 201MHz the CPU speed will be increase as well. With the multiplier at 18.5 a 1MHz increase of the reference clock takes the CPU Frequency up 18.5MHz to 3719MHz. 202MHz reference clock with a multiplier of 18.5 takes the CPU speed to 3737MHz. You can use these small reference clock increase along with .025 CPU voltage increases to find the fastest CPU frequency at any given CPU Voltage. In my case the maximum CPU speed, using the reference clock to make small changes, at 1.4V was 3755MHz. Raising the voltage to 1.425V did not improve system stability. At 1.45V the max speed was 3848MHz. Raising the voltage to 1.475V did not improve system stability.
My CPU's maximum voltage is 1.55V but I didn't want to push it. Too much voltage used over long periods can reduce the lifespan of the CPU. So 3848MHz at 1.45V is my CPU's maximum stable speed.
Overclocking a Non-Black Edition CPU
To overclock a non Black Edition CPU all of the multipliers including the CPU, CPU Northbridge, and HT Link multiplier can not be increased beyond their stock settings so we will use reference clock increases to overclock the CPU. Before we do that, because the reference clock also effects the CPU Northbridge, HT Link and memory frequencies, we need to lower their multipliers to keep these other components from causing instability. We know from our tests in Lesson 4 that this motherboards maximum reference clock speed is 270MHz. If we enter that speed the CPU, CPU Northbridge, HT Link and Memory frequencies all increase based on each components multiplier. What we need to do is lower each multiplier so that even at our motherboards maximum reference clock speed the components will be at or below their stock speed. So we need to get the CPU down to 3200MHz or lower. That is a multiplier of 11.5. The CPU Northbridge and HTLink speeds down to 2000MHz (7x) and the memory speed down to 1600MHz or below. 5.33x. So now even if we do increase the reference clock to its maximum speed in our attemps to find the CPU's maximum speed the other components will not cause instability. This isolates the CPU as being the only possible cause of instability as we overclock it. Next I'll lower the reference clock back down to it's stock setting of 200MHz and raise the CPU multiplier to it's stock setting of 16. Which gives use a resulting CPU speed of 3200MHz. Of course this makes the CPU Northbridge, HTLink and memory speed very low but that is OK. It won't effect the results of the CPU overclocking we will be doing.
I'll press esc, hit F11 to save the profile and call it CPU OC settings so we can come back to this starting point at any time. Now the method of finding the CPU's maximum frequency is essentually the same on a Black Edition CPU except that instead of increasing the CPU multiplier you can only increase the reference clock speed. You want to increase the CPU speed about 100MHz at a time. To find the reference clock speed to produce a CPU speed increase of 100MHz I'm going to divide 100 by the CPU multiplier which in my case is 16 and we get 6.25. So a reference clock increase of 6MHz will increase the CPU speed by about 100MHz. 3296MHz is close enough. You just want to go in relatively small increments.
The rest of the process is the same as a Black Edition CPU. Gradually increase the CPU frequency while running Prime95 on the Small FFT's setting for at least 20 minutes and or the CPU Coverage test at each speed. When the system becomes unstable you increase the CPU voltage by .025V at a time until the system is stable at that CPU frequency. You can then continue to increase the CPU speed to find your CPU's maximum stable speed at each voltage settings and finally your CPU's maximum stable speed at the highest voltage you are comfortable with. Remember that each CPU model has it's own maximum safe voltage. So find yours before you start overclocking by doing a Google search for your CPU's model number and maximum voltage.
In the next lesson we will show how to find your systems fastest CPU Northbridge and HT Link speed.