You can save power usage on your laptop with some manually tuning, a practise known as undervolting.

More details can be found here: http://www.nordichardware.com/Articles/?skrivelse=465

3dmark shouldn't use up full processor load though (or is this another "feature" of intel's onboard?), so it's probably a few more watts at peak.

Thanks for the link, Peter, I found RM Clock supports my core duo now. =D It already defaults to as low as it can go, but there are still a few tweaks that can be made.

Putting your harddrive to sleep may not decrease power usage, but I expect it does reduce wear and thereby increase life expectancy.

So it's not a complete waste at all.

Intel onboard video... Worst hardware ever.

Thanks for an excelent article, I alwayts wanted to know this but I didn't have the tools.
Too bad CPUs can't scale speed well. With the speedswitch XP, I am able to have my centrino pentium M 1,7GHz operate between 595MHz and 1700MHz, but I can scale it so it is 200MHz to 600MHz. Hey, Intel, I want a 100MHz-max scale :)

> a practise known as undervolting.

I undervolted my Media Center PC:

http://www.codinghorror.com/blog/archives/000221.html

.. via the BIOS, but I hadn't considered doing that for my laptop. Thanks for the tip.

> 3dmark shouldn't use up full processor load though (or is this another "feature" of intel's onboard?),

Actually, 3dmark does use 100% CPU. Games always fully load the CPU and video card. Granted that the Prime95 load tends to be a bit more intense, but it's definitely in the same ballpark.

> With the speedswitch XP, I am able to have my centrino pentium M 1,7GHz operate between 595MHz and 1700MHz

This one drops to 1/2 clock, 600mhz, when it's on battery. I guess I should have recorded power usage when it's on battery to see the difference. Hmm. I'll do that tonight.

Great information.

Now I have to get one of those kill-a-watts.

I'd be interested in what the CD or DVD consumes. My intuition says its a hefty chunk, but that's not a measurement. :)

> I'd be interested in what the CD or DVD consumes

I don't know-- this laptop has no internal CD/DVD whatsoever. There is an external one bundled with it, but I am not sure the power usage of an external CD/DVD device will be the same as an integrated internal one!

I'd have to say that I think these numbers would probably hold true...unless you have a huge monitor. I've a got a 17" widescreen and dimming the monitor usually doubles my battery life.

I've also discovered that if I forget to plug in and run Visual Studio, IIS and SQL Server 2005 with my monitor at full brightness while using wireless I can crush my battery in just under 45 minutes. I'd be interested to see how much power my laptop is using during that.

> these numbers would probably hold true...unless you have a huge monitor.

I agree, but I think you'll find that the CPU, when pegged at 100%, is still the largest consumer of power in your laptop.

I'd definitely expect power usage of the LCD to scale with size, of course!

Just buy a kill-a-watt and find out for yourself. It's a handy little device to have around:

http://froogle.google.com/froogle?q=kill-a-watt

So in your other post about 450W desktop computers, you state:

The 300gb SATA hard drive consumes 4 watts

And in this post, you state your sleeping laptop drive consumes 14 watts.

Either you're doing something wrong, or laptop manufacturers need to start putting superfast 300GB desktop drives into laptops.

> So in your other post about 450W desktop computers, you state:
>
> The 300gb SATA hard drive consumes 4 watts
>
> And in this post, you state your sleeping laptop drive consumes 14 watts.
>
> Either you're doing something wrong, or laptop manufacturers need to start putting superfast 300GB desktop drives into laptops.

I think the 14W is the *total* draw on the ammeter. Remember it was 15W with the machine on and sitting idle. So you can see that the 18W defragging is +3W for the disk at full use over idle or slightly better than the 300GB's 4W.

Its probably hard to use these types of measurements to really isolate the power consumption of individual devices and subsystems, though. Defragging will use some CPU and lots of memory, for example, so you can't just measure the increase in power and attribute it all to the disk.

Still, its a pretty reasonable approximation and Jeff's takeaways are good: you save very little trying to optimize your hard disk's awake time and save a lot if you can put up with a dim screen.

Oh, I almost forgot - "orange"

> So you can see that the 18W defragging is +3W for the disk at full use over idle or slightly better than the 300GB's 4W.

Right, the notebook drive does do a little better. And remember these numbers are plus or minus 1 watt estimates based on total draw from the wall.

I do think they're reasonably accurate. You could check the spec sheets for desktop 3.5" SATA and laptop 2.5" drives to compare-- the manufacturers do list power draw on their spec sheets.

> Oh, I almost forgot - "orange"

SHH! The spammers will hear you!

Be careful about not putting your drive to sleep. At the company I previously worked for, we used 2.5” laptop drives that were permanently powered on in one of our products. Most of the drives failed after being powered for 6 months. The manufactures design the drives specifically with the idea that they will be powered down periodically. You may want to increase the delay time before the drive is put to sleep, if waiting for it to spin up annoys you when you're working, but let it go to sleep if you're not using the computer for an extended period. It may not save much power, but the drive will last longer.

> Most of the drives failed after being powered for 6 months

Wow, that's interesting. How many is "most", and what was the sample size?

I sort of assumed people would be hibernating, sleeping, and/or generally powering off their laptops from time to time.

That's certainly far, far worse than typical 3.5" desktop hard drives do. I've had drives on for years (in servers) without incident.

Like estimated power draw, the manufacturer's spec sheets should have guidelines for the MTBF (Mean Time Between Failure) we could typically expect. This is usually expressed in # of hours.

I guess I was misled by the header:

"How much power does the hard drive use?"

Which then lists three states. I didn't realize I had to go up, determine that I should use "Laptop On, Idle at Windows Desktop" as the baseline and perform math - so what then do the other numbers mean? there are 3 numbers for Wifi - are these with the drive sleeping, at idle, or in use? Etc.

The baseline is:

"Laptop on, idle at Windows desktop 15w"

That is with wifi disabled, cpu idle, max screen brightness, and hard drive operating normally.

I'm not trying to be a jerk, but if you label a section "how much power does the hard drive use" then list the power. or the deltas from spun down. Don't make me do math to figure it all out, or rewrite your headers.

Hard drive spun up 1w
Hard drive max seeking 3w

How much power does wifi use?

On, idle 1w
On, constant transmitting from memory buffer 4w

I've been coding for small mobile devices for a number of years now. On pocket PCs, Palm handhelds and mobile phones the hierarchy of power consumption puts the display in first place, not the CPU. While this observation is due in part to the nature of the hardware, it's also due to the programming environment and the applications on them.

Applications spend the majority of their time waiting for user actions, and the OS knows that it can put the CPU into a low power mode. Properly written programs yield as much as possible. Poorly written games run in a tight update/paint cycle, which keeps the CPU at full utilization. The shortened battery life is obvious.

CPU power consumption is also minimized by the types of applications you see on these devices. You don't have a handful of applications grinding at large amounts of data while a number of background processes do other useful things. Instead, background tasks like maintaining a connection to a wireless network are handled almost entirely by dedicated hardware. There's effectively only one application at a time, and even then the user isn't going to spend an hour straight using it. The use model lends itself to long idle cycles.

thank you. that helped a lot :)

An interesting article - thanks for the effort Jeff

Thanks for the info. my laptop battery runs down to 1 volt while ac adapter is connected. WHY? THE DELL xpI. P150. TWO ICONS FOR BATTERY STAY LIT.

Does anyone know how much power a laptop consumes (typicaly) when it is plugged in and not charging versus when it is plugged in and charging the batt?

Nice article.

Has anybody done a comparison to see how much laptop screen size affects the power consumption.

I'm asking because I have a 17" Dell M1705, and am wondering if I won't be able to use it on the plane running of an EmPower plug.

I would love actually to do Kill-a-watt tests, but unfortunately I don't think this device is sold for 220V power systems ...

As a rough idea, can we assume that approximately twice the screen area would consume twice the power, or is it non-linear?

>Applications spend the majority of their time >waiting for user actions, and the OS knows that >it can put the CPU into a low power mode. >Properly written programs yield as much as >possible. Poorly written games run in a tight >update/paint cycle, which keeps the CPU at full >utilization. The shortened battery life is >obvious.

"Poorly written games", a few of which I've developed, aren't sitting around waiting for user input most of the time. They're simulating the game world.

Even tough power consumption of an optical drive was not tested, the HD numbers seem to belie my theory that you could reduce the battery impact of watching a DVD movie on a laptop if you could buffer chunks of the video into RAM (like a RAM disk, I suppose) and let the DVD drive spin down in the interim. I'd think a DVD drive would draw even more juice that a hard drive.

this is a good research.anyone has done similiar researches?
anyway i've googled and found this -> http://www.girr.org/mac_stuff/laptop_power.html
this guy is testing over his APPLE,and Jeff,i would think that maybe u would like to include the readings during Boot,Log-in and Shut down?
because from the link i've just pasted,it shows that the booting and logging consumpts a different wattage,i'm not too sure if it's same as defragmenting but i do think that it worth a test.

looking forward to see the tests by you or others. :D

Its odd that laptops would fail on constant use. I've seen a number of reports that suggest that its the start up and shutdown that causes the most damage to drives. Even the vauge google hdd survey suggested that things like operating temperature

Interesting experiment, I did the same thing to me circa-2007 Dell notebook: http://vostro.homeip.net/page?benchmarks

Half brightness, general office/internet use: 16W
This is the power consumption you can expect if you are just typing up your TPS report while browsing wikipedia.

Minimum brightness, idle, hdd on, wifi on: 11W
Half brightness, idle, hdd on, wifi on: 13w
Max brightness, idle, hdd on, wifi on: 15w
Screen off, idle, hdd on, wifi on: 9w
The difference between max and min LCD brightness is 4 watts. Turning of the screen completely saves an additional 2 watts.

Half brightness, wifi on: 13w
Half brightness, wifi off: 12w
Turning off wifi completely saves 1 watt

Half brightness, speedstep on idle: 13w
Half brightness, no speedstep idle: 15w
SpeedStep/PowerNow! definitely saves a measurable amount of electricity (2 watts)

half brightness, 1 core fully loaded: 28W
half brightness, 2 core fully loaded: 36w
Compare to idle, running 1 CPU core at 100% consumes an additional 15 watts, and two core together will cost you a total of 23 watts of additional power.

PowerPlay Max Performance(idle): 14w
PowerPlay Max Battery(idle): 13w
PowerPlay Max Performance(gaming): 36w
PowerPlay Max Battery(gaming): 32w
I used Flatout 2 as the game in this test. Naturally, gaming is one of the quickest way to drain your battery.

No disk usage: 14w
Heavy Disk usage: 17w
Constant Disk IO (with lots random seeking) draws about 3 watts of energy.

1700mhz, default voltage: 15w
800mhz, default voltage: 14w
800mhz, 0.85volt: 12w
800mhz 1 core fully loaded: 17W
800mhz 2 core fully loaded: 19w
Underclocking! By underclocking the CPU manually to 800 Mhz, I lowered the power requirement by almost 15 watts.

[sorry about the long post]

If everyone used ULV CPUs (Ultra Low Voltage) CPUs from Intel - compared to normal CPUs then we would save 70 watt since ULV's only consume 5 watt....If you use aircondition then you need another 2 watt to remove 1 watt heat..so, saving 70 watt would actually save 210 watt :-) Now multiply that by 100 million computers worldwide...that's a whopping 21 billion watt that could be saved...

It is quite sad that only super expensive Sony notebooks (Maybe also a couple of other brands, too) is being sold with the ULV version. The ULV CPU is up to 80% less consuming than even the mobile CPU's (that are rated 27 watt - for centrino).

Thanks for doing this! I recently noticed my laptop losing about 30% battery power per day it was in "sleep" mode. That seemed rather like a lot, unfortunately it was still too small a draw to register on my kill-a-watt meter. I use the sleep mode very sparingly now.

The person defending "poorly written games" is exaggerating the situation. It is *not* spending most of the time simulating the game world. Most games are poorly written in terms of power usage, in that they will use all spare CPU while in menus, while paused, whatever, because it's easy to make the game loop "draw screen, check input, run world, repeat", much easier than it is to put in "if nothing is happening wait until something is". For full-screen games I know many will use ~100% CPU while paused and unfocussed (ie. the screen of the game is *not visible*, the world is *not changing*, there is no justification for the loop still looping other than it being easier to write).

I also write poorly written games, but I don't defend the practice as reasonable. I'm just lazy. My one concession to power (because I program on a laptop and don't like it to get leg-burning hot) is to have a (default) option to cap the framerate (at 60fps) using calculated 'sleep' cycles. Also to not draw the screen when it isn't visible anyway. It's not as good as proper waiting for a message, but this way "game is paused, screen is hidden" translates to about 1000 instructions per second ("is there input? Do I need to draw the screen? How long to sleep? Sleep. Repeat * 60."), or less than 0.1% CPU usage. It's still poorly written, but it doesn't try to set fire to my legs. Bioshock, The Witcher, and basically every other modern game I've tried will, when minimised, still use 99% CPU.

Just wanted to say that I was trying to Google for laptop power consumption in sleep mode and this was the first actually useful link I found. Plus I clicked through to the main page and I have a new bookmark. Thanks!

Would like someone to test an internal CDRom drive for power consumption. I want to run linux LiveCD on my laptop while driving and without a harddrive present. Is a CD drive as bad as I expect power wise?

Lloyd, some livecds include an option to load the whole cd into memory on boot. This would reduce the consumption of power after loading. Knoppix is one such livecd, and it allows pretty good customization options. The boot option to load the entire cd to ram is aptly named "toram".

How did you actually determine how much power each component used?

Also, I've seen the new Hitachi Travelstar 500GB HDD 5K400, and Hitachi claims it uses 1.9 watts read/write and .7 watts idle. Are your results accurate? Have hard drives come that far in only 5 years, using like, 10% as much power as previous years' hard drives?

And in the cases of (these) hard drives, power consumption on idle vs sleep makes virtually no difference (I was real bored so I decided to figure out how much battery we actually save). On a 63 Wh battery (226800 joules), a hard drive mentioned in this article using 14 watts sleep 15 watts idle, uses 23.1% and 24.6% of the battery's total energy (respectively) if we use an average of about 65 watts. This means that of the 226800 joules available, we can set aside 52390.8 joules if left completely asleep, and 55792.8 joules if left completely on idle. That's a difference of 3402 joules, which means that if put asleep, we could (knowing that one watt means power usage of one joule per second) save about...53 seconds! I'm 99% sure I did my math right, but anyone who knows their physics/math, please feel free to correct me (and please only correct me if you genuinely know what you're doing 8-)

53 seconds is NOTHING!!!

When I have more time, I'll determine how much power savings there is for EACH component on high/low/asleep/idle etc etc (monitor, wifi, cpu etc).

@Jaime
Yes they do. I have one that works on 220.

Great Article.
I am thinking of purchasing the xps 1330 and while configuring it am wondering if more memory and speed will mean less up time while on batteries.
I would love 4gb of memory and internal video card and more cpu but it seems for more power on the go I need to forfeit some power.
Anyone have some proven information on this?
Seems integrated graphics is not the way to go in any case, cpu can always be clocked down so shouldnt stop me from getting as much as I want but I havent found any info to help me decide if to go for 2gb sdram to save on power or if getting 3 or 4 gb will not mean less battery time...

I realize this is a fairly old post, but I thought I'd point something out. You claim the CPU uses more power than the graphics, but I'm not sure your numbers support that claim.

What you've actually proven is that the difference between idle and load states for your graphics chip is 3 watts, and the difference for your CPU is 11 watts. That's fine, but you can't claim the CPU uses more; it's entirely possible the CPU is idling at 1 watt and loading to 12, while the graphics chip is idling at 10 watts and loading to 13.

I don't think it's likely, and I suspect your conclusion is probably correct, but you still can't claim the graphics chip only uses 3 watts. It certainly uses at least a watt or two at idle.

Thanks for this brief , to the matter writeup.

Now I don't feel myself as a the only watt killer dork on earth, really.

By the way, I use Dell Latitude D810 with a 60W Adapter with the pin purposely broken.

This serves two purposes: Firstly, instead of using 80Watt default charger, I killed some considerable watts in using a smaller Watt adapter ( heck, already considering hacking a 50W Compaq charger ). Secondly, the battery charges only if I use the Normal default 80 Watt charger with middle pin intact. I have a habit of only charging battery if the capacity is about 10%.

By doing alittle of this mess, I killed watts, and prolong the battery life . CMIIW

Thank you for this outstanding article.I thought Centrino was the best technology for laptop battery performance.

thanks,Other small improvements in battery life may be gained by the ability to turn off USB ports individually to save power.

good article，How about not keeping your laptop battery plugged in all the time. Take it out when you are using the power cord.

thanks,How about not keeping your laptop battery plugged in all the time. Take it out when you are using the power cord.

You know in my country , the PLN (national Electricity/Utility Corporation) is infested with major corruption so we love to hate the blackouts through the years. Leaving the battery attached to the battery is critical for uninterupted computing needs.

hey guys. i just wanted some information. please do help me out. I have a laptop 768 MB RAM and graphic display or 64 MB and 1.60 Ghz processor. how much power would it consume assuming at full speed and full lights on? see i'm trying to have some of my electronic devices work on solar power and am rather keen on doing some environment friendly acts ( apart from cutting my bill ). And knowing my country, solar stuff is pretty new here....

please write me at rak108@gmail.com

Can someone tell me how much it cost per hour to run a satellite 2450-101 laptop computer, assuming 100 hours per month.
cheers

So does a laptop consume more power if you charge it when it is off rather than having it on without battery?

HAS ANYBODY GOT AN ANSWER TO PASQUALIE'S BLOG 29TH JUNE.
CHEERS.

Hi

Try this link:
http://michaelbluejay.com/electricity/howmuch.html

computer coupons and price drops
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" Putting your hard drive to sleep isn't worth it. Ever. You save a whopping.. single watt. Why bother? "

Wait. Putting your drive to sleep, saves you almost 14W of power, not just a single watt... Note: cpu idle uses 15W of power, which is the state your computer would be in, were it not in sleep mode.

Also - as a matter of saving your battery life, since every battery has a life determined by the number of times it is completely discharged and subsequently recharged.
Whenever you have access to a power outlet, plug your laptop in. This way the battery doesnt get discharged, thus prolonging your battery life.