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Lesson 06 - CPU Northbridge and HT Link Overclocking

Introduction

Before we move onto memory overclocking we need to find our systems maximum CPU Northbridge and HT Link speed the default speed of both is 2000MHz.  The CPU Northbridge is the cache on the CPU and the memory controller on the CPU.  You want the CPU Northbridge speed to be at least 3 times the speed of the RAM.  

Our RAM speed is 1600MHz.  This is double data rate or DDR ram so the actual speed of the RAM is 800MHz.  800 times 3 is 2400 so we want our CPU Northbridge speed to be at least 2400MHz.  If you have 1333MHz RAM you can divide it by 2 and you get 666.5 so your actual RAM speed is 666.5Hz.  In this case the CPU Northbridge speed is fine at default because if you multiply 666 times 3 you get 1999.5 or 2000MHz.  However since we are going to show how to overclock your RAM to be faster than the stock 1333MHz speed you will want some extra CPU Northbridge speed to make sure the system is running at its best.  

According to AMD a HT Link speed of 2000MHz is all you need to get the best performance in most cases.  However certain memory intensive programs can see a performance advantage with a higher HT Link speed.  For the HT Link speed we will shoot for 2400MHz as well.

We need to make some changes for the CPU Northbridge and HT Link speed overclocking tests.  I'll hit F12 to load a profile and choose Default which we set up in Lesson 3. Hit esc and go into the MIT.  This set all of the frequency and voltage to manual with their default settings.

First we will show how to find your systems fastest CPU Northbridge and HT Link speeds using a Black Edition CPU. Then we will show how with a non Black Edition CPU.


Overclocking the CPU NB and HT Link on a Black Edition CPU

For Black Edition CPU's the CPU Northbridge and HT Link multipliers are unlocked so we can increase them beyond their stock setting.  The default multiplier for both is 10. 10 times the reference clock speed of 200MHz gives us 2000MHz which again is the default for both.  A multiplier of 11 gives us 2200MHz.  The system can probably handle this speed for both components so we will begin with a multiplier of 11.  A multiplier of 12 gives us the 2400MHz speed we need to keep up with the RAM speed and will probably require an increase to the CPU NB voltage to keep the system stable.  The next available multiplier is 13 which would overclock the CPU Northbridge and HT Link to 2600MHz. It's highly unlikely even with a large increase in the CPU Northbridge voltage that the system will be stable at that speed.  So to find our systems fastest stable CPU northbridge and HT Link speed we need a way to make smaller changes.  Increases to the reference clock is how we will achieve these smaller increases to the CPU Northbridge and HT Link speed.

We will overclock the CPU Northbridge first and then the HT Link.  We are going to be testing the CPU Northbridge using both multiplier and reference clock increases so we need to lower the multiplier for the CPU, HT Link and Memory to make sure that even with the reference clock increases we make they stay at or below their stock speeds.  We'll first set the CPU Northbridge multiplier to 11x.  We probably won't be able to get the CPU Northbridge speed above 2500MHz.  If we divide 2500 by 11 we get 227 so the highest reference clock speed with will need is 227MHz.  I'll make that settings change and that increases the speeds of the other components above their stock speeds.  I'll use their multipliers and get them at or below their stock speeds so there is no way they could be the cause of any instability while we overclock the CPU Northbridge.  I'll set the reference clock back to 200MHz. Hit esc and F11 to save this profile and I'll call it CPU NB OC Test, esc and Go back into the MIT.  

We need to increase the CPU Northbridge speed about 50MHz at a time.  The multiplier is 11 so a reference clock increase of 5MHz will raise the Northbridge speed by 55MHz.  We can see the speed did increase from 2200MHz to 2255MHz.  We then need to save and exit and go into Windows.  Run Prime95 on the Blend setting for 20 minutes. {reg}If the system remains stable you need to go back into the BIOS and increase the reference clock by 5Mhz and test again, increasing the reference clock until the system becomes unstable while running Prime95 on Blend. When the system does become unstable you will need to go back into the BIOS and increase the CPU Northbridge voltage by on notch, go back into Windows and run Prime95 on Blend at that same speed.  Continue using this process until you have found your systems maximum stable CPU Northbridge speed.  Make sure you keep notes on the speeds, the multiplier and reference clock used to get there as well as the CPU Northbridge voltage required to make each speed stable.

On our system 1.175V was required to reach 2442MHz on the CPU Northbridge with the reference clock set to 222MHz and the CPU Northbridge multiplier set to 11. Further voltage increases did not produce a faster stable CPU northbridge overclock.  After you have your maximum CPU Northbridge speed restart and go into the BIOS. The HT Link speed can not be faster than the CPU Northbridge speed so there is no way to isolate the HT Link speed.  This is OK because we know the amount of CPU Northbridge voltage need to make the CPU Northbridge stable at it's current speed of 2442MHz. Change the HT Link multiplier to 11.  In our case this game us a HT Link speed of 2442MHz which is equal to our CPU Northbridge speed.  Save the settings and boot back into Windows to make sure both the HT Link and CPU Northbridge speeds are stable by running Prime95 on the Blend setting for at least 20 minutes.  If the test fails go back into the BIOS and set the HT Link multiplier to 10 which will give you a HT Link speed of 2220MHz.  Run Prime95 in Blend mode to verify it's stability. 


Overclocking the CPU NB and HT Link on a NON Black Edition CPU

If you have a non Black Edition CPU the process is very similar.  I'll press F12 and load the CPU NB OC Test profile and go into the MIT. The difference being that you can not increase the CPU Northbridge and HT Link multipliers beyond their stock setting.  Once again it's unlikely the CPU Northbridge and HT Link will run faster than 2500MHz.  The stock multiplier setting for both is 10. If we divide 2500 by 10 we get 250.  So the fastest we will need to run the reference clock for this test is 250MHz.  I'll make that change and all of the speed settings update.  I'll change the multiplier of the CPU, HT Link and memory multipliers so they are at or below their stock speeds.  Next I'll set the CPU Northbridge to it's stock setting of 10.  2200MHz is a good safe starting point for the CPU Northbridge so I'll set the reference clock to 220MHz.  10 times 220 gives us 2200MHz.  You want to increase the reference clock about 50MHz at a time.  With a multiplier of 10, a 5MHz increase on the reference clock will do the trick. Go into Windows and test for stablility in Prime95 on the Blend setting for 20 minutes.   Another increase of 5MHz to the reference clock will raise the CPU NB speed to 2300MHz.   Continue increasing the speed until the system becomes unstable.  

Come back into the BIOS and increase the CPU Northbridge voltage by one notch, go back to Windows and run Prime95 on the Blend setting again at the speed that previously failed.  Continue using this process until you have found your systems maximum stable CPU Northbridge speed.  Make sure you keep notes on the speeds, the multiplier and reference clock used to get there as well as the CPU Northbridge voltage required to make each speed stable.

On our system 1.175V was required to reach 2440MHz on the CPU Northbridge with the reference clock set to 244MHz and the CPU Northbridge multiplier set to 10. Further voltage increases did not produce a faster stable CPU northbridge overclock.   After you have your maximum CPU Northbridge speed change the HT Link multiplier to 10.  In our case this gave us a HT Link speed of 2440MHz.  Save the settings and boot back into Windows to make sure both the HT Link and CPU Northbridge speeds are stable by running the stability test for at least 20 minutes.  If the test fails go back into the BIOS and set the HT Link multiplier to 9 which will give you a HT Link speed of 2196MHz.  Run Prime95 in Blend mode to verify it's stability. 

We now know our systems maximum stable CPU Northbridge and HT Link speeds and the frequency, multiplier and voltage settings used to produce them.

In the next lesson we will find our memories maximum stable speed.


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