Running a Haswell in Nominal Mode
So you have bought or built a computer with a Haswell processor. First off, you need to enter the BIOS to set up standard parameters. You can usually do this by selecting an option called "Load Optimized Defaults" or something but the name is rather misleading. This set of parameter values is not actually optimal. It only ensures basic system functionality. You cannot rely on it to achieve maximum performance or minimum power consumption. Let's first discuss how you can make your computer more economical.
For all their downsides, Haswell processors must be given credit for requiring less power when idle in comparison with LGA1155 processors. Unfortunately, mainboards don't make this advantage available to you by default. None of the mainboards we've tested enables all of Intel's power-saving technologies, so you have to do that manually. Some technologies may be enabled by default, but most often they are set at Auto. Don't be misled into thinking that that's enough. Auto may mean anything: enabled, disabled or any numeric value you can think of. If you know what an option does, you should always substitute the ambiguous Auto with a specific value.
Enabling all of the CPU-related power-saving technologies lowers the computer’s power draw by 3 to 8 watts without affecting the computer’s performance. A properly set-up LGA1150 platform will need a mere 30 watts in idle mode (up to 40 watts with a high-end graphics card like an AMD Radeon HD 7970). So the mentioned technologies save you 10 to 20% of the total power consumption, which seems to be a lot, especially as ordinary computers spend most of their time in a power-saving or standby mode.
Unfortunately, these options are often hidden somewhere deep in the BIOS interface. Following the alphabetic order, we’ll first show you ASRock’s BIOS. It contains such power-saving options in the CPU Configuration subsection of the Advanced section.
One of the options is even off by default. You should turn it on and explicitly Enable each of the others.
It is hard to reach the power-saving parameters of ASUS mainboards as if they were hidden deliberately. You have to open the Advanced section, move to CPU Configuration, and then switch to the CPU Power Management Configuration page.
You can only see the first three options because CPU C States is set at Auto and the rest of the options are hidden. When you change it to Enabled, you will reveal them. Most of the power-saving technologies are already turned on, so you only have to switch Package C State Support to Enabled.
By the way, you may also want to take a look at the CPU Power Management subsection of the Ai Tweaker section. Its options pertain to the voltage regulator integrated into Haswell processors and some of them may be used to lower the computer's idle power draw.
Browsing through ASUS’s BIOS, you can also find the DIGI+ Power Control subsection where the mainboard’s power system is set up. Such subsections can also be found in the BIOSes of other mainboard makers who have implemented digital voltage regulators, e.g. Gigabyte's 3D Power Control and Advanced Power Settings or MSI's DigitALL Power. We habitually set CPU Phase Control or PWM Phase Control at Balanced or Optimized although we fail to note any positive effect from doing so. We had long suspected that some mainboards had lost the ability to dynamically change the number of active phases in the CPU power system depending on load. The lines of LEDs that had used to indicate the number of active phases disappeared from Gigabyte and MSI mainboards while ASRock doesn’t let you check it out through its exclusive software anymore. Intel’s mainboards are the only ones that don’t hide anything, so they come with Voltage Regulator Status LEDs just as before. You can even choose the indication mode with them (constant glow or pulsating light) or disable the indication altogether.
It is not clear if you should enable the exclusive power-saving technologies implemented by specific mainboard makers. This option is called “Power Saving Mode” in ASRock’s BIOS and “EPU Power Saving Mode” in ASUS’s BIOS. We used to think that the economy was achieved by lowering voltages, but that’s not so simple, actually. These BIOS options affect Intel's Turbo Boost technology which varies the CPU's clock rate depending on current load. The benefits will be noticeable not only in idle mode (as with Intel's power-saving technologies) but also at high loads. However, lowering the power draw at the expense of performance doesn't sound good for many users. That's why you may want to check out what exactly those technologies do, benchmark your computer's performance before and after turning them on, and make sure you are satisfied with the outcome.
On Gigabyte mainboards, CPU-related power options can be found on a BIOS page called "Advanced CPU Core Settings" or "Advanced CPU Core Features". It doesn't matter which BIOS interface you use, by the way. If it is the new Gigabyte UEFI DualBIOS, you should open the Frequency tab of the Performance section.
If you prefer Gigabyte’s classic BIOS, you will find the necessary page among the Advanced Frequency Settings of the M.I.T. section. The classic interface offers the same options as the new Dashboard, so it doesn't limit your tweaking opportunities in any way.
We often find fault with MSI mainboards, particularly with their BIOS options, but it is MSI’s BIOS that offers the easiest access to the CPU-related power-saving technologies. You can find them at the bottom of the OC section, in the CPU Features subsection. The OC options are all closed in a loop so you can reach them by simply pressing the Arrow Up button once.
Take note that the C1E Support option is disabled by default and you should turn it on along with the Intel C-State parameters. One of indisputable advantages of MSI mainboards is their low power consumption. However, like mainboards from other brands, they do not use all of Intel’s power-saving features by default. Enabling those features will give you extra savings.
With the power-related parameters of your Haswell CPU set up, you can proceed to overclocking it. Or you may want to check out the rest of the BIOS options and see if their default values are optimal. Take a look at the memory subsystem, for example. Your DDR3 modules are likely to be able to work at a higher clock rate or with lower timings. Moreover, mainboards from different brands may have their peculiarities which must be taken into account.
For example, on an ASRock mainboard the exclusive Power Saving Mode may be enabled by default although it lowers performance. You may also find that the memory voltage is set too high, up to 1.6 volts.
Mainboards from ASUS and Intel cannot keep the CPU clock rate at its standard level when the CPU load is very high. They drop the clock rate because the default power limit on the CPU is exceeded. It is not a serious problem, though. It doesn’t show up at all under ordinary loads and even when it occurs, the performance hit is negligible. However, there are a lot of different factors affecting the overall performance of your computer, so you may want to make sure that each of them is set up right. In this particular case, you should increase the CPU’s power limit. On an ASUS mainboard, it is done in the CPU Power Management subsection of the Ai Tweaker section.
On Intel mainboards, you should open the Performance section for that. Then you select the Cores block on the left to see the required options on the Config tab.
How much higher should you set it? You can set the power limit at a few hundred or even at the maximum possible value. The limits are only there to keep the CPU within the required power consumption and heat dissipation targets. Of course, we assume that you’ve got a well-ventilated computer case and an efficient CPU cooler. Even this is not so, your computer shouldn't come to harm as protective technologies are supposed to trigger on in case of overheat and enable thermal throttling, drop the clock rate or even shut the computer down altogether. On the other hand, there is no reason to run such risks by using your CPU under unfavorable conditions.