In Intel Core i7, i5, and i3 systems, practically all of the important frequencies (like the CPU and RAM speeds) are simply multiples of the base clock rate (BCLK) for the system, so as you increase BCLK to overclock the processor, they'll all get overclocked (by default). However, most of these components use multipliers, which can be lowered to limit their impact on finding your maximum BCLK.
In this guide, we'll cover exactly how to take the RAM, CPU, iGPU, and QPI frequencies out of the equation, and then we'll go over actually finding the upper limit for BCLK. Once you have that, you'll have what you need to overclock your processor.
Note: This article is part of our ultimate overclocking guide: How to Overclock: Intel Core i7, i5, and i3 CPU Overclocking Guide, so if you arrived directly to this page and are confused by anything mentioned here, try checking out the main guide. It explains all of the basics to overclocking i7, i5, and i3 systems.
Remove the Limiting Factors
Take the Memory Speed Out of the Picture
Memory Speed = BCLK * Memory Multiplier
The only way to take the memory out of the picture is to reduce the memory multiplier to its lowest setting, which will run the memory at its lowest speed.
Go ahead and do whatever it takes to set your memory to its lowest speed. On the ASUS P7P55D-E Pro, you don't have to mess with a multiplier at all. You can just change the memory speed directly by changing DRAM Frequency in the Ai Tweaker section in the BIOS, but on other systems, you may need to lower the memory multiplier directly or change the memory ratio.
Keep the CPU from Limiting BCLK
Next we need to take care of the CPU, and we'll handle this the same way we handled the memory: reducing its multiplier.
The CPU multiplier is very easy to spot in the BIOS. With the ASUS P7P55D-E Pro, it's also in the AI Tweaker section, and it's called CPU Ratio Setting. Set this to something low like 12, which will keep the processor speed below its stock value, so we'll know it isn't affecting BCLK*.
* If you happen to get your system up to a BCLK of 220 (which is definitely on the high end for BCLK), your CPU will only be running at 220 MHz * 12 = 2640 MHz, which is well within its limits.
Stop the iGPU from Holding Us Back (Clarkdale CPUs Only)
Clarkdale i3 and i5 dual core CPUs have an Integrated Graphics Processor (iGPU) inside of the processor that handles all of the graphics for systems without a discrete video card, and the iGPU is also linked to BCLK, so it can get overclocked as we increase BCLK (depending on your motherboard).
Disable iGPU if you don't need it
Most overclockers probably have a dedicated video card, so if you do, you should just disable the iGPU, so you won't have to worry about it. There should be an option to do this in your BIOS.
Unlink iGPU from BCLK
However, if you do need the iGPU's integrated graphics, you should either:
- Unlink the iGPU from BCLK, so that it always runs at its default speed.
- Lower the iGPU's frequency, so that, as we up BCLK, it won't ever go higher than its default.
Most new motherboards have the first option available, so I'd recommend going that route if you can. Exactly how you do either of these options depends on your motherboard, so consult your motherboard manual or support site if you need help.
Some older LGA 1156 based motherboards are unable to change the iGPU frequency with the original BIOS, so make sure you update your BIOS if you don't see an option for changing this.
Since the iGPU is linked to BCLK, it can also be overclocked to improve its performance, but I'd recommend doing that after you've overclocked the rest of the system.
Lower the QPI Frequency
It's also a good idea to lower the QPI frequency or multiplier to its lowest setting in the BIOS (there are usually only two options for it), since it can limit overclocking BCLK.
What Can We Realistically Expect Out of BCLK?
The default BCLK for i3, i5, and i7 systems is 133 MHz. If you're shooting for 4 GHz with an i5-760 with a default multiplier of 21, we'd need to get BCLK up to 4000 / 21 = 190, and on the i5-750 with a default multiplier of 20, we'd need to get it up to 200.
200 is usually pretty easy to do for BCLK, so it really shouldn't be a limiting factor for a 4 GHz overclock. Most systems can usually overclock BCLK to around 205-210, and if you're lucky, maybe in the 210-220 range.
Determining Your Maximum BCLK
Now that we've isolated BCLK from as many components as we can, let's see how high we can get this thing to go.
The integrated memory controller (IMC) inside of the CPU is one of the things that doesn't have a multiplier of its own, so it's one of the things that's going to get overclocked as we increase BCLK, and it will likely be what limits overclocking BCLK. Therefore, as you try to overclock BCLK, the VTT voltage(aka IMC) is what you'll need to increase.
Manually set VTT to its default value
The default VTT voltage is 1.1 V, but as we increase BCLK, your motherboard may manually increase this on its own--which we don't want--so if your default memory voltage is less than 1.6 V, manually set your VTT to 1.1 V, and if it's greater than 1.6 V, set it to 1.15 V. We're doing this because VTT should never be more 0.5V below the memory voltage.
Next, change BCLK from 133 to 150. Almost all systems should do this without a problem. Now, boot into windows.
If you get into windows fine, run the quick Prime95 system stress test for about 5 minutes. If you don't see any errors, then you're in good shape.
However, if you do get an error or the system freezes or reboots, you'll need to go into the BIOS and increase the VTT voltage. I'd up it by 0.025 V at a time. Once you do that, you'll want to go back to the previous step and run the Prime95 stress test again.
Once you're stable, increase BCLK by 10.
Keep increasing BCLK by 10 and stress testing until you hit one of the follow road blocks:
- You reach your desired BCLK.
- You hit the maximum VTT that you're willing to try. Remember: Intel's absolute maximum for the VTT voltage is 1.4 V, but I'd recommend keeping this below 1.35 V to be safe.
- Increasing the voltage isn't helping anymore.
Once you've hit one of those road blocks, go back to your last successful attempt, and try upping BCLK by a finer increment, such as 5. If this passes, try upping it again by 2. If it doesn't, try lowering it by 2. Keep doing this until you find your maximum BCLK.
Once you've found it, I'd recommend lowering it by a few MHz and running Prime95 for about an hour to make sure it's nice and stable. If it fails, try lowering BCLK until it does pass. Once it passes, congratulations, you've found your maximum BCLK.
This article is part of our ultimate overclocking guide: How to Overclock: Intel Core i7, i5, and i3 CPU Overclocking Guide.
If you're following along in the guide, the next section is Overclocking the CPU.