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Hardware: Power Consumption

How much power does your PC Consume?

Much discussion has been generated as a result of the August 14th 2003 power failure, and subsequent requests to conserve power, as to how much power a PC workstation or server consumes. The main question being asked is whether-or-not it is better to power it off at night-time. In response IST has does tests and would like to present the following pros and cons relating to powering off your PC.

According to tests conducted by IST, Hardware Support, tests showed the following. On a Pentium 4, 1.7GH machine:

  • during boot power in watts is close to 110w
  • during idle, no power management,. close to 60w
  • during full power saving, no hard disk spin, machine in sleep mode, 35w

The monitor consumption was not included in these tests. Also, number will vary depending on the processor you have and what other peripherals you may have connected.

This means that each PC consumes roughly the same amount of energy at it's highest usage level as a 100w light bulb.

A Sony 17" monitor, by far our most common, consumed 75w when in use. When power-saver mode kicks in (and the monitor goes black with a yellow indicator light) the power consumption is negligible to the point that our test equipment did not even register any power use.

The total power consumption of a typical PC and monitor does not consume more than 175 Watts of energy at its highest rate. At night time when your PC is "sleeping" it only consumes 35 Watts.

As mentioned power consumption varies depending on hardware. There is a PC Power Consumption Calculator available online at: if you wish more details.

The bottom line is you would conserve more energy by shutting off one 40 Watt overhead florescent light bulb than your PC at night time.


To power off or not?

There are several factors at play here. They include the following:

  • There is virtually no power-saving advantage to powering off your CRT monitor. The energy consumed to keep your tube warm may extend the life of the monitor itself and in the end may save the University more by leaving it on.
  • If your PC is managed:
    • You are better off leaving it on as operating system patches will be delivered to you overnight and your PC will be patched by morning. If you power it off patches will still be delivered but not applied until the next scheduled application time. In Academic Support this is 5am the next morning.
    • In terms of Virus Protection, you are again better off leaving your PC on. Virus definitions will arrive overnight and a full scan of your PC will happen at that time. If you power it off you will still receive virus definitions when the PC comes up, but you will have missed the scanning window and have to wait until the next scheduled scan. If this time is again at night time, your PC may never actually get scanned. To make matters worse, if you turn off Real-Time Scanning, (the feature that scans a file when it is opened) you could easily be infected.
  • If your PC is client managed (meaning you manage it yourself):
    • Obviously the sooner you patch your operating system the more protected you are from viruses and hackers that will take advantage of it. Windows XP has the ability to automatically do Windows Updates. If this is not utilized do manual updates on a regular schedule. Since you are choosing the method and the schedule you are the best one to decide whether-or-not to leave your PC powered up.
    • The same is true of anti-virus updates. Choose a schedule that best suits your work schedule and make sure your PC is powered on then it is scheduled.
  • Some hardware like Hard Disks fail less when they are never powered off. There may be a hardware cost associated with powering your PC every night.

According to the Daily Bulletin on Monday August 18th, "On a typical workday, UW is using about 13 megawatts of power". According to Dennis Huber (vice-president administration and finance), is quoted in this same bulletin as saying: "The "base load", or minimum consumption, is about 4.5 megawatts". This means if the 1000 Academic Support department PC's that IST administers were all left on overnight they would only consume 35 kilowatts or of 1% of total load.

Created by: Manfred Grisebach, IST - Systems, August 20th , 2003