Writings on technology and society from Wellington, New Zealand

Thursday, April 23, 2009

Sucking up the Juice

Today on Radio New Zealand National I talk about the energy consumption of computers and how you can do your bit to keep that down.

Read below the “more” for my speaker notes, or download the audio as ogg or mp3.Technology slot with Colin Jackson for Thursday 23rd April 2009

Q: Energy – do computers use a lot of energy?

A: The short answer – not very much in most home situations, but it depends how much compute power you have and how old your computers are..

Q: So an average PC in a home?

A: Up to a few hundred watts while it’s running – less for many machines.

Q: We just leave them running, don’t we?

A: Yes, that is rather the point of having a broadband Internet connection – that you can just walk up to your computer and check email instantly, or anything else that takes your fancy, without having to wait for a computer to start up. Modern computers all have a ‘sleep’ mode and you should always set this up to operate automatically on any machine that’s not a server.

Q: So why do computers use power – what do they do with it?

A: The short answer is that they turn it into heat. And some scientists say that’s inevitable – there’s a thing called Landauer’s principle, named after an IBM scientist. Landauer’s principle says that, if you destroy information you increase entropy, which means effectively that something will get hot. This is the consequence of the Second Law of Thermodynamics. That law says that the amount of entropy in a system tends to increase, and entropy means disorder. In physical systems, disorder is heat. Incidentally, this law is called “Time’s Arrow” by some, because it points to an inevitable irreversible degeneration of the universe, as it becomes more and more disordered.

The processes used inside computer chips to manipulate information involve keeping some bits of information and getting rid of some other bits. So, as well processing information, they are destroying some, which leads to heat being generated by the processing chips. Now, in a modern computer, there are many chips, but just two which are likely to be subject to this effect – that’s the main processor chip and possibly another one which is a specialist chip to drive the screen. Both of these chips have millions or probably billions of transistors on them and each of those may destroy information as the process it, so these chips get hot.

If you look under the covers of a modern computer, you won’t be able to see the main processor chip because its covered in a large lump of metal, called a heat sink, which has cooling fins and generally a fan attached to it to help keep it cool. If you let the chip get too hot it fries and your computer’s no more good – hence the fan. And your computer will probably have other fans in it to help shed the heat. A good rule of thumb as to whether a computer is an energy hog is: just how noisy is it? Would I be happy to have this machine running in my bedroom? You should aim to get as quiet a machine as you can.

Q: So what uses the energy – the computer getting hot or the fans to get rid of the heat?

A: Both do. That’s one of life’s ironies, really – we don’t actually want the heat in the computer, it’s wasteful and damaging, and we have to spend yet more energy – in turn generating more heat and noise, to get the heat away from the computer.

If you go into a data centre – that’s a room or a building that exists to house computer servers – there’s a few things you’ll notice straightaway about the racks of equipment. Firstly, it’s quite noisy – every machine has fans in, and its usually fairly chilly because there are some really big air-conditioning units spread around the walls. Racks of computer servers can consume a lot of power, and that almost all ends up as heat that the air conditioning has to get rid of. And the air conditioning itself uses as much energy, or more than the machines its trying to keep cool. A modest data centre might use a megawatt, say, which would be enough for hundreds of homes. Bigger ones use tens of megawatts. This is serious amounts of power.

Q: What about the impact on the environment?

A: There are valid concerns about this. A couple of years ago, someone tried to estimate the energy consumption of the Internet. Now, I’m not qualified to check his figures, but they are quite alarming. He found that the Internet was responsible for over 8% of the US energy bill, and over 5% of the world’s energy bill. Frankly, those figures seem high to me. And they don’t allow for all the activities that would take place if people weren’t using the Internet – like flying to meetings instead of meeting by Skype or email.

The cost of running these data centres isn’t cheap either. They need to be sited in locations where they can get good power. Building them is expensive. Companies are trying to be a bit innovative about this. Google has a patent on a offshore data barge – they have a vision for a floating data centre, out where it doesn’t pay land rent or property rates, using power it gets from the waves. I’m not sure if that will ever happen. And Microsoft has announced that it is building its data centres out of shipping containers – they fit up a container in a standard configuration full of racks and what-have-you, then they can move containers in an out as they need.

Q: What advice can you people about reducing the power costs of their computers?

A: Get modern machines and don’t buy more power than you need. You might be the sort of person who enjoys driving a V8 and you’re prepared to pay the fuel costs, but many people just want to get form A to B in a car that suits their needs without using petrol than they have to. So, unless you are into online gaming or movie editing, don’t buy machines that are touted as suitable for those activities. Laptops tend to use less power than desktops, so remember that when choosing.

If you have any old style glass tube computer screens left, consider replacing them with LCD panels. Panels use far less energy, they don’t take up as much room and they are far easier on your eyes.

Unless you have an energy guzzling machine, I wouldn’t turn it off most of the time. They use almost no power unless they are active. But you do need to set it up so the computer will go to sleep after you’ve ignored it for 15 minutes. That’s easy to do, look for Power Management in Control Panel on a Windows machine or in System Preferences on a Mac, and I’ve linked up some instructions in today’s links.


2006 white paper on PC energy consumption, and another about home computers. Top ten ways to save energy if you have computers.

The Internet is estimated to use 5% of global energy. Hmmm.

How to engage power management in Windows XP, Vista, and Mac OS X

Landauer’s Principle and the Second Law of Thermodynamics

Google patents the offshore data barge, and Microsoft is building it’s servers into shipping containers

posted by colin at 11:07 pm  


  1. Regarding electrical/electronic equipment failing when it’s turned on—yes, it does still happen. Did you hear about the recent Seagate firmware bug afflicting their newer 750GB and 1TB drives? That could cause the drive to fail when it was turned on.

    Comment by Lawrence D'Oliveiro — 23 April 2009 @ 12:24 pm

  2. First, congratulations on building a
    website with stretchy pages that let folks with poor sight read the content in large fontsize without having to endlessly scroll. Others should learn to do this.

    Second, energy efficiency is of immediate interest to many of us. I’d be interested to know what the consumption difference is between Hibernate and Standby.
    I’d also like to know if there’s any way one can get a scheduled function (eg automated data backups) to be followed by a Hibernate function. Would this be something written into the backup software itself or something provided by a separate piece of software? Thanks for the ongoing interest provided by your articles and radio talks.

    Comment by Annmarie Armstrong — 23 April 2009 @ 1:16 pm

  3. “If you have any old style glass tube computer screens left, consider replacing them with LCD panels. Panels use far less energy…”

    Why then do people say that modern (LCD) TVs use more electricity then old (CRT) ones?

    Comment by Peter Lynch — 23 April 2009 @ 3:42 pm

  4. Annemarie – thanks very much for your kind comments.

    There is no standardisation that I am aware of on the terms ‘sleep’ and ‘hibernate’ across different manufacturers. Technically there are a variety of things a computer can do such as shut down its drives and/or its processor.

    The short answer is that anything is better for power consumption than leaving the entire computer active. I’d suggest trying each option on your computer. What you want is for the display to go blank, the computer to fall completely silent, and that it can be woken in a few seconds by shaking the mouse or pressing keys. If you can achieve this you have greatly cut the energy cost of running the computer but you still have access to it whenever you want.

    Peter – I’ve not heard anyone say that LCDs are less efficient than CRTs. I have heard it said of plasmas, which are thirsty beasts, but it’s unusual to use those as computer displays.

    The main energy consumption in an LCD is the fluorescent light behind the LCD panel (remembering that an LCD switches existing light; you need to illuminate it somehow to make it into a computer display). Some modern LCD displays have LED illumination which is brighter and more efficient.

    CRTs by contrast are a giant radio valve. They need to be got hot just to work, hence the slow start up time. And they require exotically high voltages. Ugh.


    Comment by colin — 24 April 2009 @ 9:26 am

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