Overclocking.Guide

Note: Overclocking might lead to a loss of warranty and damage components. However, if you follow the instructions of this guide, you should not experience any issues. If you want to know more about the risks of overclocking, simply check out this guide.

Haswell is the 4th generation of the Intel Core series. After Ivy Bridge, this step is a so-called “tock” which means Intel invented a new microarchitecture in the same 22 nm manufacturing process like Ivy Bridge. The next generation, Intel Broadwell, will be a “tick” which means the Haswell architecture will be reduced to 14 nm.

Compared to Ivy Bridge, Intel changed some major parts of the CPU. The VRMs are now in the CPU itself.

This means the mainboard will only provide one voltage to the CPU – the Input-Voltage. Everything else will be transformed inside the CPU itself.

Another major change is the Ring-Bus. This bus is the connection between the CPU cores, system agent, cache (LLC) and shared cache. This connection is now also connected to the base clock of the CPU and also overclockable with a simple multiplier same as the CPU core frequency. A higher Ring-Bus clock will result in a higher performance.

The CPU core clock is a result of the Base-Clock (BCLK) and the multiplier of the CPU. Same goes to the memory clock which is also a result of BCLK and a multiplier.

Example:

101,47 BCLK x 44 Multi = 4464 MHz CPU Clock
101,47 BCLK x 24 Multi = 2435 MHz RAM Clock
101,47 BCLK x 40 Multi = 4058 MHz Ring Clock

Assuming you are using a CPU with “K” suffix, the overclocking will be very easy. It’s possible to just increase the CPU core clock by raising the multiplier in steps of 100 MHz. However, I recommend to adjust some more settings in order to achieve the best overclocking results.

If you have a CPU without “K” suffix, you have to increas the Base-Clock to overclock your system. Usually I don’t recommend this, because the BCLK is tied to the PCI-Express clock and DMI-Connections which can cause instabilities even though your CPU is still stable at the given core clock.

Some Intel CPUs feature a so-called turbo clock. For example the i5-4690 has a stock clock of 3500 MHz on all cores with a turbo clock of 3900 MHz on a TDP of 84 W. This means if you run an application which is only single threaded, the CPU can clock up to 3900 MHz on one or two cores, because it doesn’t reach the full load of 84 W.

You can change this limit by raising the maximum TDP in the BIOS to e.g. 150 W and also manually raise the multilpier of all cores to 39, so you have a constant full clock of 3900 MHz on all cores.

Reminder: Always keep an eye on your temperatures. Haswell and Devils Canyon CPUs have a maximum temperature of 105 °C. However, I recommend to stay below 90 °C to prevent long term damages.

 

Overclocking Step-by-Step

This is a general guide for all kinds of mainboards. The approach is the same on all boards, however some voltages or settings might be named differently. You will soon find more guides made for specific mainboards.

Step 1: Voltages

Offset, adaptive or override?

Offset means you add or subtract a voltage from the stock voltage. The stock voltage is set by the mainboard and differs from CPU to CPU. The advantage of this setting is that you can still use energy saving options, so the CPU lowers the voltage in idle. However, the offset value is still added or subtracted to the lower idle voltage.

Adaptive is similar to offset, but the voltage is added or subtracted in idle. This means you will only see the voltage change under load.

Override completely erases all settings applied by the mainboard. You will always have the same voltage, no matter if load or idle. This can improve the stability of your CPU if you run very high clocks such as 5000 MHz.

For moderate overclocking without any risks you simply have to fix the voltages at their stock values first. So go to the BIOS, read out the stock voltages and fix them. The voltages are related to CPU and mainboard and differ from setup to setup. These are the stock values of my setup:

Vcore: 1,05 Volt
Vccin: 1,80 Volt
Vring: 1,015 Volt
Vccsa: 0,85 Volt
Vccioa: 1,015 Volt
Vcciod: 1,015 Volt
DRAM Voltage: 1,50 Volt (depends on the memory kit you use!)

For normal Haswell CPUs the Vccin voltage should always be 0,4 V higher than the Vcore. So if you raise the Vcore to 1,50 Volt, you should use at least 1,9 Volt Vccin.

However, some Devils Canyon CPUs like to have very low Vccin voltages. I experienced improvements on some CPUs when I lowered the Vccin to about 1,6 Volt.

Usually the stock voltages are safe settings and you can already overclock your CPU without raising these values. This means you don’t risk high temperatures but still gain free performance.

 

Step 2: BCLK and Multiplier

In addition to the voltages, I recommend to manually fix the BCLK and multiplier. Set the BCLK to 100 MHz in the BIOS and the multiplier to 41, so you will start with 4100 MHz. Most 4770K/4790K/4670K/4690K CPUs will be able to boot with this clock on stock voltage, however some might be already unstable at this core clock.

The ring will slightly improve your performance as well. However, it can get unstable very quickly. I recommend to fix it at 35 (3500 MHz) at the beginning.

Simply try to boot into windows and check with Prime 95 if your system is stable. (Here is a simple guide how to use Prime95)

 

Step 3: TDP-limit and energy saving options

Some energy saving options will cause the CPU to clock down in idle. These features are called C-States. If you don’t want your CPU to lower the core clock, simply disable C1E and C3/C6. This might be needed if you push your CPU to really high clocks.

Depending on which motherboard you use, it might be necessary to adjust the TDP-limit of your CPU. If you can successfully set the multiplier to 41 in Step 2, you can skip this and continue with Step 4. Otherwise, disable the Turbo option or adjust the Turbo power limit to about 150 W. If possible, I always completely disable the Turbo, to have my CPU constantly at the same clocks on all cores.

 

Step 4: Adjust your RAM settings

A common mistake is to ignore the memory settings. If you buy e.g. a 2400 MHz memory kit and just mount it in your computer, it will not automatically run at these clocks since they are not officially supported by all CPUs or motherboards. In order to get the RAM to run properly, you have to adjust the settings manually or load the XMP (Xtreme Memory Profile) settings.

If the XMP does not work, you can set the clocks and timings manually. Simply enter the main timings (CAS Latency, tRCD, tRP, tRAS) according to your memory and adjust the memory frequency. Also don’t forget to fix the memory voltage. Some kits are specified at 1,65 Volt. If you have such a kit, go the voltage settings and adjust DRAM voltage (Step 1).

Note #1: The most “K” suffix Haswell CPUs have very good IMCs and should do 2400-2666 MHz without any issues. However, if you experience issues with high memory clocks, it might be necessary to raise the Vccsa, Vccioa and Vccioa voltages. You can read more about this later in advanced overclocking.

Note #2: Intel Haswell CPUs officially only support memory kits with 1,50 Volt and lower. But I never experienced issues with higher memory voltages. From my experience, it’s absolutely no problem to use 1,65 Volt kits on Haswell.

 

Step 5: Test your settings with Prime 95

To test your settings I recommend to use Prime 95. Keep in mind to keep an eye on the temperature during the stability test. You should not exceed 90 °C.

Here is a simple guide how to use Prime 95

If your system is stable at the given clocks and voltages and stays below 90 °C, you can increase the clocks and see if it’s still stable. If the system crashes and you are still below 90 °C, simply increase the core voltage (CPU VCORE) in small steps e.g. from 1,050 Volt to 1,075 Volt and test again.

 

Advanced Overclocking

Voltages

The following table shows all important voltages for Haswell, explanations and the recommended values for your usage.

 

Loadline Calibration

Since Intel moved the VRMs from the mainboard to the CPU itself, the Loadline Calibration doesn’t really help anymore and I recommend to not use this feature.

 

BCLK Strap

The BCLK strap is another multiplier which affects the BCLK overclocking. Usually this feature is only unlocked on “K” suffix CPUs such as 4770K.

The BCLK strap is a multiplier between BCLK and the rest to improve overclocking and reach higher core or memory clocks. Available multipliers:

x 1 (100 MHz – stock)
x 1,25 (125 MHz)
x 1,66 (166 MHz)
x 2,5 (250 Mhz – doesn’t work)

Here is an example, so you understand how it affects your system.

 

Questions or suggestions about this guide? Simply leave a comment and I will reply as soon as possible.