The silicon powering modern microprocessors consumes significantly less wattage than consumer technology leading up to this point. Look back at the GTX 400 series (Fermi) for an example of this: The flagship GTX 480 was 250W, and it ran damn hot, too. NVidia acknowledged this when we toured their facilities, noting that the complaints of noise, heat, and power consumption directly impacted the development of Kepler units. To put things into perspective, the GTX Titan also draws 250W and has approximately 2.5x the transistors over the GTX 480 (7.5B vs. 3B).
Despite the overall trend toward improved power-to-performance ratios, a mid-range gaming machine can still easily pull 500W+ under full computational (CPU/GPU) load -- that's a lot of power. Even idle, without BIOS advanced power saving features configured, you could easily be resting on a couple hundred watts. Personally, I've got almost a constant system up-time, and that consumes a lot of power. In order to mitigate power consumption and the electric bill (~$20 / mo. with full up-time on my machine, dropped to $10 / mo after taking these steps), we can use modern advanced power saving states implemented by Intel and AMD.
Because our most up-to-date test benches use Intel products, I'll be writing most of this guide referencing those C-states and power saving options. Haswell adds a couple of very impressive power saving functions, like DevSleep for SSDs and S0iX (active idle) for the CPU itself, though
I'll also go into some of the basic video card controls found in various control panels (MSI Afterburner, EVGA Precision, etc.), including fan speed curves to minimize power consumption when idle.
Starting with the Easy Stuff: Hardware Controls & Accessories
In my recent "What Next?" guide, I provided sample hardware upgrades and basic mods for post-build systems. As a starter to power control and monitoring, a couple of these items might be beneficial to more fine-tuned tweaking; if power conservation is highly important to your usage applications (read: 24/7 uptime or home server / HTPC environments), it could be beneficial to look into:
Granted, a hardware fan controller isn't at all required to modulate fan speeds. BIOS and application-layer utilities can automatically or manually control fan speeds by voltage throttling (using PWM fans, especially).
CPU & GPU Software Fan Modulation
Fair note: The fan modulation changes will largely yield insignificant power savings, but can improve the overall life of the fan bearings and decrease overall system thermals. Power delivery is more efficient when the system is cooler on the whole, so a cooler machine means higher power efficiency driven to the silicon.
These quick changes will improve the overall life of your bearings (and thus, your system), minimize noise emissions, and marginally reduce power draw. You'll need these tools:
Most UEFI BIOS menus hide their CPU and System Fan speeds under a "hardware monitor" tab. Locate that tab in your board's menu. Some configurations might have the fan speeds to 100% or other high values; by setting system fan speeds and CPU fan speeds to "auto," the platform will increase voltage delivered to the fans during times of intense load or thermals. If you've got a pretty good handle on your system's thermals and feel confident in manually setting a low speed, that can also be done through these menus. As a rule, we generally recommend always leaving the CPU fan setting on "auto."
System fan settings should also be visible in this panel (if you're not using hardware controllers to regulate their voltage). Search for "System Fan 1," 2, 3, etc. and make appropriate adjustments. If the fans are PWM (pulse-width modulated), "auto" mode will modulate voltage based upon system demand and thermals. A manual setting (like 60% or 40%) will also work, just make sure you have a good understanding of your system's thermal requirements.
Check HW Monitor from your OS to validate the fan speeds. Min, max, and present values will be highlighted. Use these to check if your changes have applied.
Let's move to Afterburner or equivalent software. With MSI Afterburner -- which should be compatible with all cards -- users can set a custom fan speed curve to gradually increase speed with load. See below:
In this example, I've set a custom curve to keep the fan at 40% speed until the GPU hits 30C. Once it hits 30C, the speed very gradually increases to 55% until the GPU hits 65C. At this point, the fan speed jumps sharply to 80%, aiming to rapidly dissipate heat. The objective of a curve like this is to keep the GPU under 80C by using short, bursted, high fan RPMs to minimize annoyance to the user and maximize cooling to the GPU. It's a trade-off between noise and cooling, and a curve like this accomplishes it well.
This lowers your overall system thermals and noise, which increases power efficiency and extends fan longevity by using voltage modulation.
OS-Layer: Windows Power Saving Options
I'm not going to get too in-depth here, since most of us are familiar with Windows, but it's pretty important to briefly mention. Windows has built-in sleep and hibernate states that can dramatically reduce power consumption by individually powering-down unutilized components. This includes magnetic hard drives (spin-down to lower RPMs), the CPU (put unused components to sleep), GPU, and even SSDs (DevSleep in Windows 8).
As many of you likely know, putting a system to "sleep" suspends its active session to RAM, so RAM will retain power while all other components reduce their own consumption. Hibernate stores data to the physical disk, and thus often requires large chunks of storage to enable (4GB+). This makes it sub-optimal for SSD usage, but if you pass hibernation through a hard drive with more storage, it's an easy choice.
Restoring from the disk or powering down the RPMs of a disk will take a while for the system to restore itself (can be seconds to a minute, depending) given the nature of a physical platter spinning-up.
All of these settings can be accessed through Control Panel -> Power. We'd recommend configuring your own power profile that suits your needs. Disabling the screen when idle, spinning-down the HDD, and activating some level of sleep are all recommended. Hibernate is nice, but can often introduce system instability with some OS/hardware configurations. Keep in mind that S3/S4 power saving states will destabilize the system when using certain overclocking settings (check the manual for your board).
Pre-Build Buying Options
Before jumping to BIOS, I wanted to offer a couple of pre-purchase build options that could dramatically affect overall system power performance:
Time for power saving BIOS settings. Hit Page 2 for those.