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A single desktop computer will consume approximately £75 of electricity per year if it is left on all the time. If a computer is put into a low power state when it is not being used this cost is likely to fall to £15 per year (insert reference).This figure extrapolated to the estimated 720 000 computers in UK Universities equates to an annual saving of around £40 million. There are a wide range of assumptions in these headline figures so each organisation is advised to gather information about usage patterns, computer power consumption and electricity prices.
Switching computers into low power states when they are not needed is more difficult than turning off a light bulb or television. People familiar with the way insitutional computers are used will recognise at least some of the following scenarios:
- Users may need to be asked to leave their computer on for at least one day a week so that a central backup service can make a copy of files overnight
- Computers may need to be left on all the time in case there is the need to install software updates or security patches
- Users leave their computer of all the time so that they can use it remotely to for instance retrieve a file while at a conference
- Computers are left on so that people do not have to wait for it to start up or boot
- Desktop computers are used as a web server or file store
- Desktop computer is used to keep another computer on ("keep alives")
- Computer is used to constantly filter emails so that email folders are organised when accessing an inbox via the web
- Spare computing capacity is used by computer modelling projects e.g. SETI, climateprediction.net and GRID experiments in general
- Standby (S3) and hibernate (S4) power saving modes cannot be implemented reliably
It is possible to implement a range of technical initiatives that can be used to allow computers to move into low power states more often. Organisations may also decide that some practices should be discouraged.
Tools and techniques
Enabling users to wake computers up remotely
It is possible to provide the ability for IT managers and end-users to wake computers that they own using another computer. By providing a facility to turn computers on remotely, it becomes possible to ask people to turn their computers to low power states more often. For instance, many organisations will ask their staff to leave their computers on so that the a backup service can access the hard drive and create a copy of files. If computers can be woken up by the backup service then users can switch them off without disrupting this essential activity. This same logic applies to other services that may need access to a computer more regularly e.g. services that install software updates, anti-virus checking and so on.
Case study: University of Oxford
[http://wiki.oucs.ox.ac.uk/ltg-public/lcict:wol_oxford_university The University of Oxford wake-on-LAN infrastructure] enables IT officers, end-users and managers of 3rd-party services to wake computers remotely.
Configuring computers to move into low power states automatically
Most computing devices are built to be able to detect when they are not being used. Desktop computers have four main power states: On (S0), sleep or standby (S3), hibernate (S4) and off (S5) which can be triggered manually, automatically after a pre-configured amount of time, and remotely via