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Minnesota State University, Mankato
Minnesota State University, Mankato

Going Green

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Energy Savings

Did you know that MSU’s electricity bill was over $1.8 million last year? In a time where everyone is looking for ways to cut costs, save money, reduce carbon footprint, and preserve the environment, there are things you can do to help cut our energy bill and go green too.

Some ideas are obvious – like turn off lights when no one is in the room or when you leave the office/classroom (you do this at home, right?).

Another way you can save money is to turn off your computer when you leave work. People occasionally ask if it’s better to leave a computer on or shut it off and the answer in most cases is to shut it off when it’s not in use. This will both save energy and extend the life of the hard drive and monitor.

How significant are the savings? Our own Dave Esping measured the power use of several different types of computers and monitors. What he found was that leaving your computer idle was like leaving a 40-88 watt light bulb burning 24x7. Turning your computer off, putting it to sleep or hibernating it when you leave will reduce energy consumption by about 73%.

LCD and LED computer monitors use very little power and only consume about 1 watt in energy saving mode.

But some of you know that it may take a long time to start up your computer in the morning – which might be the reason why you don’t want to shut down your computer at night.  PCs and Macs have two alternatives for you to use to cut power and get to work faster in the morning.

Sleeping and Hibernating

Both modes freeze the current state your computer is currently in. Say, for example, you have web browsers open to where you are doing research, your e-mail is open, you’re working on a Word document and trying to correct an Excel formula. When you sleep or hibernate your computer in the afternoon, then power it back up in the morning, all of your programs are where you left them the afternoon before. You just log in after a very quick boot-up and you’re ready to continue working.

There is a slight difference between sleep and hibernate. Sleep freezes the programs and goes into a low power state, so there still is some ‘brain activity’ because the computer’s memory is still being powered and refreshed while the hard drive and other devices are powered off.  In contrast, during hibernation, the computer’s state is frozen, memory contents are copied to the hard drive and then everything is powered down. Therefore, sleeping reduces power consumption, while hibernation eliminates it. Now, if your computer is asleep and there is a power outage, your computer will have to do a full system boot-up and unsaved work may be lost. (The exception is with Vista, which uses a hybrid sleep, so if there is a power interruption Vista will recover as if it were hibernated.) Hibernation will bring everything back regardless if power was removed. It offers added benefits of lower power consumption and more reliable recoverability of your work.

Another difference between hibernation and sleep is the time it takes for your computer to ‘wake up.’ In sleep mode, some computers bypass power on tests and your computer might be up and ready to log in within 5 seconds. Hibernation may take 15 to 30 seconds to get ready to log in on some computers since it has to copy the contents of memory from the hard drive to memory first. (Your mileage still may vary.)

Have a laptop? Hibernation is the way to go because it won't use battery power while it's hibernating. If you put a laptop to sleep, the battery will eventually drain and, upon your return, you'll be back to a full system boot with a dead battery. So with hibernation, not only will your boot up time be reduced, but your laptop will be ready to go much more quickly and your battery live will be preserved.

Here’s the link to the results (broken link). Some interesting results show that laptops use much less power (20-30 watts less power than desktops), and Macs use much more power when sleeping than Dells.

Introducing Problems?

There is a possibility that sleep or hibernation will result in some computer issues – like sound not working, or you may find out that your computer does a full system reboot rather than waking up quickly. The ability for a computer to successfully sleep or hibernate will depend on the devices in it and the software and driver’s ability to recover gracefully from a sleep or hibernation state.

If you find that your computer doesn’t have a sleep or hibernate option, please call the Help Desk at 389-5993 for assistance in enabling these options.


Saves files and closes running applications and then powers down your computer. When you power your computer on, the computer does a health check, checks files on the hard drive for functionality, boots up the operating system, checks for devices connected to the computer, loads drivers, as well as other programs that need to be ready for you to log in, and finally presents you with a login prompt. After logging in, you must open applications to begin working or communicating.
Keeps applications open and running in memory, but stops hardware devices and enters a low power state. Power keeps memory running an monitors keyboard or mouse activity. When the power button is pushed again, hardware devices are started and all running programs are still open and ready to use just as when the computer was put to sleep. Time to start up is a matter of seconds, versus tens of seconds booting from shutdown. (NOTE: If a computer is sleeping and power is disconnected, any program data that is in memory may be lost and the computer resumes just as if it were completely shut down.)
Hardware devices are stopped, and the contents of memory are written to disk and then power is shut down. When the computer is powered back on, memory is copied back from disk and then hardware devices are restarted. All programs that were running are still open and ready to be used just like they were when the computer was sent to hibernation.
Windows 7 introduced hybrid sleep that puts the computer to sleep, but it also copies memory to the hard disk. In case of no power interruption, the computer wakes from sleep instantly. If power is interrupted while asleep, it wakes up from hibernate.

The difference between hibernate and sleep is that in sleep, even though power is reduced, it must still be maintained in order to successfully return from sleep. In hibernation, the computer powers down and if power to the computer is disconnected, all programs and settings will still be ready to use. Vista uses a combination of hibernation and sleep.

So what is the best option to use?

  • Laptops - The best option is hibernation, because no battery is drained while the laptop is not in use. Mac laptops will sleep until the battery is depleted and then it will hibernate.
  • Desktops - Windows 7 hybrid sleep will go into low-power sleep as it also hibernates. In case of power interruption during sleep, all programs and data apps will always be ready to go in seconds. Macintosh desktop's sleep mode will greatly reduce power when not in use and will wake up in seconds so you can get to work quickly. For Windows XP, either sleep or hibernation is the best option, depending on how long it takes to wake up from hibernation.

Pass on your ideas to save energy to Bryan Schneider.