Appendix G: Auditing and Evaluating Power Management in Personal Computers

An audit of the hardware and software computer professionals supervise can help clarify the potential and actual power management capabilities of their equipment . An audit can be of one particular system, or of a large set of systems. When many similar systems are audited, there are economies of scale, but many PC system characteristics need to be individually checked since both hardware and software details can vary for systems which may appear identical.

Audit types

We have divided audits into three types, from the most simple to the most rigorous. The procedure for each succeeding level incorporates the earlier levels.

Level One

Observe brand and model information by visual inspection of the outside of the case, without relying on the machine being on. A level one audit can be combined with power ratings and likely use patterns to indicate overall electricity use rates and potential savings from power management.

Level Two

Examine configuration settings in any appropriate BIOS screens and control panels, observing the presence and configuration of any relevant software (such as screensavers, video or network card drivers), and potentially contacting the manufacturer for any power management information they can provide. A level two audit indicates the overall degree of enabling and whether some machines are configured in the same or a similar state.

Level Three

Measure the power drawn by the device over enough time to observe all important power management modes occurring, recording the amount of time between mode changes and the power level at each mode. A level three audit may also include opening the PC case and temporarily removing some expansion cards. A third level audit verifies that potential power management modes actually occur, and that power and timing are as expected from the configuration and equipment inventory.

Guidance

For some equipment, contacting the manufacturer may be necessary to obtain information about how to check, interpret, or change system configuration. From the serial number, the manufacturer can also tell the date of manufacture and the configuration-as-shipped status. For any audit, an initial walk through of the audit area should be done to evaluate the general types of equipment present. It is often easier to conduct audits when most people are not around, such as on nights and weekends.

First level Audit

The first level of audit generally takes only that information visible from the exterior of the device. For the most part this is "nameplate information" found on the back panels of the PC or monitor, particularly the Manufacturer Name, Model Number, Serial Number, Manufacturer Date, and rated current or power draw (in amperes or Watts). Manuals for the PC or monitor may provide information about default power management settings, or if add-on software is provided. Also, check to see if the monitor is plugged into the PC convenience outlet.

Try recording whether the equipment was on during the audit, and if so, what state (e.g. full-on, visibly in suspend, running a screensaver, etc.). This can help indicate how much energy is being saved by power management, and how much more could be saved by enabling more power management or turning equipment off when not in use. Then, if the machine is on and in a suspend mode, press a key or move the mouse and record how many seconds it takes to revive to the full-on state. You can use this information to decide on delay times appropriate to each piece of equipment.

Second Level Audit

A second-level audit begins with rebooting the computer to observe any relevant information (e.g. amount of memory, number and size of hard disk drives) as the system comes up. To determine a model number, it is sometimes necessary to check what type of system the operating system thinks it is running on. It is also helpful to know the version of operating system. You should be able to determine power management details such as the number of power management modes it supports, whether it supports APM, whether power management is enabled (and how), the power management options available and the delay times.

For monitors, you may want to record the number of options for screen saver or other power management software, whether power management is enabled, if video card software is present, the type of screen used for screen saver or screen dim, the number of power management states it supports, and the delay times specified.

Dynamic Testing: Second or Third level

To see if power management actually occurs, it is necessary to turn the system on and wait till delay timers in the system have had a chance to run out and attempt to initiate power management. This can be done with or without power metering, though without one can only observe monitor power management and hard disk drive spin-down. These can be noticed through any delays in returning to full power, or often in the case of the disk, by its sound.

Compare observed times with those listed on the configuration screens (or monitor manuals). Note if screensaver defeats monitor or PC power management; this may require waiting until the screensaver has a chance to begin operation which may be well after the power management begins.

Once the dynamic test is complete, if any changes were made to the power management configuration, return the system to original setup parameters unless the user requests otherwise.

Third Level Audit

A third level audit requires a current or power meter; it is preferable to have two such meters available, to be able to measure both the PC and the monitor at the same time. Because of the effort involved, dynamic testing is most commonly used when there are many machines of similar manufacture so that the lessons learned from studying one will apply to many others.

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Return to the PC User Guide table of contents and home page.
Return to Appendix F: One-page Summary.

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This web page last modified by Brian Pon on April 27, 2000.
Questions? E-mail Alan Meier.