Sunday, November 25, 2012

Things you can do to lower the power consumption of your PC.

If you are someone who keeps your PC running 24/7 for whatever reason, you should be concerned about how much power the PC is drawing. A PC that runs 24/7 will definitely show its presence in your monthly power bill. A typical PC would draw about 60W at idle but a high-end, all-purpose PC would draw like 100W or even more. That's when doing nothing at all. And that too, without the monitor being turned on.

You could build a pretty power efficient, but very capable PC if you did some research at the time of building it. You don’t really have to spend much money either. Only choosing the components carefully will suffice.

For example,
  • buying a PSU that suits your PC, instead of going overkill
  • buying a mini-ITX or micro-ATX motherboard instead of going overboard with and ATX motherboard with all the features you can possibly get
  • buying 2 sticks of low voltage RAM instead of 4 sticks of regular RAM

But not all hope is lost. There are still a few things you can do to lower your PCs power consumption.

CPU – under-volt / be conservative with the overclock

CPU is one of the two components that are responsible for majority of the power draw in your PC. (Other being the video card.) Hence if you can lower how much power is drawn from the CPU, you will essentially save a significant amount of power.

If you are running your CPU at stock clocks (i.e. no overclocking is done), and if your motherboard allows undervolting the CPU from BIOS/UEFI, you might be able to shed some watts off if you drop the CPU core voltage (Vcore) a notch. Usually, the Vcore that is automatically set by the motherboard is kind of a "safe" and "more than enough" voltage, but if you experiment with the Vcore - that is, if you lower it slowly and stress test before lowering any further - you might be able to lower the Vcore by about 10%. Vcore has a noticeable effect of the power consumption. For each 10% drop in Vcore, you will be able to save 19% of power (theoretically speaking). There are no claims that undervolting would harm the CPU as overvolting would, so you don't have to worry about trying out this technique. The worst thing that might happen is your would get a blue screen when stress testing the CPU. If you get a blue screen, that means you have gone too far. Up the Vcore a bit and try again. Do this until the CPU is fully stable. (Read the "Number Crunching And You: Stressing Your CPU" part in this article.)

If you are overclocking your CPU, you still can keep the power consumption under control. Be conservative with the Vcore. If you need to up the Vcore by 5% for a 2% higher clock, it doesn't seem worth it. There is always a sweet spot. After that, you will get diminishing returns. I recommend keeping all the inbuilt power saving features turned ON even when you overclock your CPU. It might or might not limit your maximum overclock - but I think you should stop upping the clocks any further if you cannot do with with the power saving features turned ON. You can always disable then if you are going for the world record, but for day to day usage, stick to a conservative overclock. It will keep your CPU cool and will be less harmful to the CPU.

Hard drives – use the OS power saving features

A typical hard drive would use up to 10W when they are in use; about 5W when idle. But there are some that come on top when it comes to power consumption. One of those drives was the Samsung HD204UI, which was - alas - discontinued because Seagate bought Samsung's hard drive business. That drive used less than 4W when sitting idle doing nothing. (I know, it is not much, but it all adds up. If you had 3 drives, then the difference between Western Digital Green drives and these would be 7W - and that's at idle.)

OK. 5W at idle, 10W at load is not huge, but if you have half a dozen hard drives in your PC, it all can add up to some noticeable amount of power. So, how do you save power drawn from the hard drives?

There is one thing you can do. Turn the hard drives off. Not unplug them, just turn them off. Let's be realistic. You might have many hard drives in there, but you don't access them all the time. You might even not access some for the entire day. So turning the hard drives that are not in use seems like a viable idea. But you don't do it manually. Let the OS do it automatically. Use the power options dialog to do it.

You can set the drives to go to sleep after 5 or 10 minutes of idling. (I believe that the system drive never goes into standby, especially if you have a PageFile in there.) The downside to this is that when the hard drives are sleeping and you want to access data inside that drive, you have to wake it up. Everything is automatic, but it would take a few seconds for the hard drive to wake up. You will see a delay before accessing the data.

Video card – use V-Sync

This is the main culprit when it comes to the high power consumption of a modern PC. A high-end video card may use up to 200W power when their muscles are flexed. But the good thing about the current generation of video cards is that for the first time both AMD and nVidia have improved the power efficiency. We can expect cards with even better power efficiencies in the future.

There isn't much you can do if you've already bought your video card. They do have inbuilt power saving mechanisms just like the CPUs do. They automatically go into low power states when they are lightly used.

But there's one more thing you might be able to do.

Heard of Vertical Syncing? It means that the frame rate will be synced with the refresh rate of your display, which is typically 60Hz. The purpose of this is to get rid of the phenomenon called “screen tearing”. But subsequently, you get reduced power consumption from the graphics card if your video card was capable of delivering more FPS than the refresh rate of the display in the first place.

But there are two – yes, 2 - catches. One is that when you limit the frame rate, you get higher input lag than what you get with a higher FPS. You might click your mouse button, but it will take longer to take effect. It’s not a big difference. We are talking in terms of milliseconds, but that could be the difference between killing and getting killed in Battlefield Multiplayer.
The other one is that if your original frame rate dips below 60fps, it will get locked to 30fps. Unfortunately that's how it works. However, if you have an nVidia graphics card, they have a new feature in the driver called Adaptive V-Sync which can disable or disable V-Sync depending on the frame rate "on the fly". That is a great way to get the best of both worlds.

Another thing you can do is to lower the idle clocks of the video card. Modern video cards use very little power at idle compared to few year ago. You might be able to save couple of watts at best, but it might get unstable or you might get strange screen artifacts in certain situations. Try it if you are adventurous.

Motherboard – disable unwanted features

There are so many unwanted features listed in the BIOS/UEFI screen that you can disable. Floppy disk controller, 3rd party SATA controllers, FireWire name it. It is always better to disable these things because the more the controllers you have to initialize at boot-up, longer it takes to get into the OS. Further, you can install a minimum set of drivers and that's always a good thing. Drivers are what usually crash the OS. Having less drivers to worry about means the chances of a driver issue sending the PC down the hill becomes lower.

It is not conclusive that it lowers power consumption if you disable these additional features in the motherboard. There could be a slight reduction because instead of being in standby or running state, not they ought to be in shutdown state. The best thing would be to buy a motherboard with the features that you need or you might need in the future. (it's always better to plan ahead how you would expand the PC.)

Just for your information. Mini-ITX and Micro-ATX motherboards usually use much less power than a regular ATX motherboard. So if you went with one of those, you are in luck. Also, motherboards that are optimized for overclocking - i.e. comes with a power supply that uses more than 8 phases - usually use more power. They might do alright when the CPU is loaded, but high number of phases usually kill the idle power consumption.

Fans – use a fan controller

Fans draw very little power, about 2W for low RPM models. But high RPM fans, especially ones with high static pressure can draw 4W or even more. If you have 5 fans in your case, that's a significant amount of power of overhead.

There are a couple of things you can do to lower power consumption of the fans.

First, you can remove the fans that don't really do much. Remove the fans that are disrupting the natural air flow due to convection.

You can lower the speed of the fans by changing the input voltage to 7V or even 12V. Check out this guide on how to do it. Sure, it will lower the airflow, but it will also make the fans much quieter - if you didn't need the high air flow in the first place. I don't like PCs that make a lot of noise. I would walk the low noise path even if it increases the temperature inside the case by a couple of degrees.

But the best thing you can do - if your motherboard supports it or you have a "capable" fan controller - is connecting all the fans to the controller and let the fan speed be automatically controlled according to temperatures. I have a manual fan controller and I always forget to increase the fan speed if there is a need. It never works. Automatic controlling is the best. You will either have to use BIOS/UEFI or the software that came with your motherboard or fan controller or you might even be able to use Speed fan. (Here is a guide on how to use Speed fan.)

Optical drive – just get rid of it

Just get rid of that optical drive if you don't need it. It's as simple as that. There is no other way you can take to lower the power consumption. If you want to have it so that you can install Windows from the disc, make and store an ISO file of the disc on the hard drive, then either use the USB install method or install from the hard drive itself. Then you can get rid of the optical drive if that was the only thing holding you back.

Monitor – use the OS power saving features

If you are not sitting in front of the PC, there is no need to keep your monitor turned on, so turn it off. Some people would just run a screensaver. Running a screensaver is no good in this case. It saves the screen from burn in, but it doesn't save any power. In fact, it might actually increase the power consumption because of the animations in the screensaver.

If you forget to turn off the monitor manually, which is quite natural, set it to automatically do so using the power options built into the operating system.

Further, I would lower the brightness and contrast levels as much as comfort or picture quality allows me to. But put comfort and screw quality in the driving seat. Don't just go crazy and lower them to the absolute minimum.

OK that’s it folks. If you think missed anything, fire up in the comments section. I will add them to the list as well.
All of the above apply is if you have already built the PC. What if you are going to build a new PC soon and are concerned about power consumption? That’s just brilliant. We can attack right from the beginning. We can choose the right components and not worry about it later. I guess you know what my next article is gonna be on. Winking smile
Go green!


  1. I actually use speedfan to reduce the noise level. lol. it saves power too :D

  2. I stopped leaving a PC on 24/7 around 3 years ago. Main server has been scaled back to a SU2300 Nvidia ION which acts as a NAS/HTPC(xbmc). With a pico PSU idle is ~19W

    A couple of weeks back I scaled back even further with an android tablet which runs 24/7 and wakes the NAS on demand ;) ~4W

    1. I definitely would have built a NAS i wasn't living in a small Japanese apartment. It would have made a lot of things simple. But, I don't want to build another PC. Off the shelf NAS's are darn expensive anyways.

      I am also testing the WOL features of the router. I really don't have to keep the PC turned ON 24/7 as of yet. That need would materialize when I get a tablet next year.


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