Should you Overclock with SpeedStep, C1E, or Turbo Boost Enabled?

Most overclocking guides start off by saying:

  1. Disable all power saving features, such as SpeedStep, C1E, and C-States.
  2. Turn off turbo boost and hyper-threading.

They usually tell you this because these features can limit the maximum overclock on some motherboards. However, this isn't always the case anymore, so it's not that cut and dry. Therefore, depending on your motherboard, you may have an option with these, so let's explore them a little further.

Power Saving Features: SpeedStep and C1E

SpeedStep and C1E work to lower your CPU voltage and multiplier when the system isn't busy. This lowers your power usage, and therefore, the heat that your processor produces.

However, when you're overclocked, you're running at higher speeds than default, which usually requires more voltage, so if your voltage is dropped too low for the speed it's running at, this could cause your system to become unstable.

However, some newer motherboards, such as the ASUS P7P55D-E Pro, don't have this problem because they use a new feature called dynamic vcore.

Dynamic Vcore

Dynamic vcore lets you set a voltage offset that gets added to or subtracted from the voltage that would be set by default (instead of setting one fixed voltage that never changes). You can see what this looks like in the ASUS P7P55D-E Pro BIOS by looking at the picture below.

dynamic vcore in bios

All of Intel's newer CPUs have different default voltages depending on what multiplier is currently being used, so if we're using an offset to set our voltage (instead of a fixed voltage), our offset will be added to or subtracted from the default voltage for the multiplier that the processor is currently using.

Dynamic vcore can allow us to overclock with the power saving features and turbo boost enabled

Because of this, dynamic vcore will usually allow us to overclock with all of the power saving features turned on because it will still add our voltage offset to whatever voltage these features set, so our voltage never drops too low to make the system unstable.

Similarly, since turbo boost is also based on changing multipliers and voltages to achieve a higher speed when the system isn't fully taxed, our offset will also get added to these new voltages, so we're also able to overclock more easily with turbo boost turned on.

Hyper-Threading

Hyper-Threading allows each CPU core to work on up to two threads at once, instead of only one. All of Intel's new i7, i5, and i3 processors use hyper-threading, except for Lynnfield's quad core i5 CPUs: the i5-760 and i5-750.

Overclocking with hyper-threading enabled will probably limit your maximum overclock, since each core is getting hotter by doing two things at once. Most overclockers disable this feature for that reason. Most programs still don't fully utilize more than two cores, so it might not buy you much leaving it enabled (if you don't use heavily multi-threaded applications).

You can always compare your overclocking results with it both on and off, so you'll be able to see if it's worth it to leave it on.

So, what should we do?

Leave the power saving features on if you use dynamic vcore

So, based on what we just went over, if your motherboard supports dynamic vcore, I'd recommend leaving all power saving features on. They didn't affect my maximum overclock--on or off--so why not benefit from the heat reduction and power savings?

Turbo boost can sometimes help you achieve a higher overclock

Additionally, if your motherboard supports dynamic vcore, turbo boost may also be a viable option if you're having a hard time achieving a high overclock with all four cores loaded.

For example, one of my i5-750 CPUs would only stably overclock to about 3.9 GHz when all four cores were stressed in Intel Burn Test, but it could reach 4.3 GHz when only one or two cores were stressed. This is an ideal case for overclocking with turbo boost on, and I'll explain why.

The maximum turbo multiplier for an i5-750 is 24, so to reach 4.3 GHz, I needed to be running at a BCLK of 4300 / 24 = 180. When more than two cores were busy, the multiplier would be dropped from 24 to 21, so I'd then be running at 180 * 21 = 3780 MHz.

Although overclocking with turbo boost did lower my 3 or 4 core frequency from 3.9 GHz to about 3.8 GHz, that's only about 100 MHz, which will hardly be noticeable when running heavily threaded applications. However, look at what we got for it when we're only using 1 or 2 cores. Single or dual threaded applications will now run at 4.3 GHz, so we gained 400 MHz, which is a significant difference. Additionally, most programs don't fully utilize more than 2 cores, so you'll be running at near 4.3 GHz most of the time.

Leave turbo boost off at first

However, I'd still recommend trying to overclock without turbo boost at first, so you'll be able to see how high you can get without it. If you can get a high enough overclock without turbo boost, it's probably not worth turning it on, since you'll likely face more than a 100 MHz penalty when 3 or 4 cores are loaded. Either way, it depends on your situation and whether or not you use a lot of multi-threaded programs.

What Next?

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 .