Configuring Advanced Configuration Power Interface (ACPI)

Objective:

Configure Advanced Configuration Power Interface (ACPI).

The Advanced Configuration and Power Interface (ACPI) specification delivers consistent power management to a Windows XP Professional computer. Because Windows XP communicates directly to the ACPI interface, the operating system can coordinate and direct power so that the system is available when users need it, when applications need it, and when the network or peripheral equipment needs it. At the same time, Windows XP can shut down unnecessary components to save power if the system is not currently active. The difference between the ACPI architecture and earlier power management schemes, such as Advanced Power Management (APM), is that the earlier ones interfaced with the BIOS but did not coordinate with the operating system. This turned out to be ineffective.

Some of the benefits of ACPI are

• Power efficiency for laptops, such as dimming the LCD panel when the laptop is using a battery, or turning off the LCD when a user closes the lid.

• Applications that are capable of using power management features notifying Windows XP when the computer can be put to sleep. This feature, for example, prevents a computer from going into hibernation during a presentation.

• Wake-on support that enables the computer to respond to events that require it to wake up. An administrator could wake up the computer to transmit a print job to its print device.

• Device integration with power management so that a device can ask Windows XP to put it into a low-power state when not in use.

Non-ACPI-compliant components in a Windows XP computer, whether software or hardware, can prevent ACPI from placing the computer on standby. These components can also cause errors or loss of data if the computer wakes up and the component is not prepared to function.

Power configuration is performed in the Power Options utility in Control Panel, which is shown in Figure 7.13. You can access this same utility from the Screensaver tab of the Display Properties dialog box.

Figure 7.13. ACPI power management is configured in the Power Options utility.

The first tab in Power Options lists the Power Schemes. Each scheme allows you to configure the length of time that the computer is idle before you turn off the monitor, turn off the hard disks, or go into standby. When using a laptop, you can set separate time valuesone that applies when the computer is plugged in and another that applies when the computer is running on battery power. Six power schemes are configured with optimal settings for various needs, such as when showing a presentation, or when trying to minimize power consumption. You can customize any of these schemes to meet your needs.

Laptops include two tabsAlarms and Power Meter. The Alarms tab enables you to set the notification for when a battery reaches a low state, and when the battery reaches a critical state. You can set how these alarms act when they are achieved, such as putting the computer in standby, sounding an alarm, or forcing a shutdown. On the Power Meter tab you can see whether the laptop is running on power or battery, as well as how fully the battery is charged.

On the Advanced tab, you can configure the computer to show the power icon on the taskbar. You can also configure the computer to prompt for a password when it wakes up from standby. For a laptop, this tab enables you to configure the action the laptop will take when you close the lid or when you press the power button.

The Hibernate tab lets you enable hibernation, which means that the computer writes the entire amount of data in RAM to disk and turns itself off.

If you have a Uninterruptible Power Supply (UPS) connected to the computer, a UPS tab appears in Power Options. This tab lets you check the status of the UPS and configure its options, such as how long to provide power to the computer from the UPS after a power failure.

An APM tab appears if the system is not considered to be ACPI-compliant. This is for backward compatibility.

Exam Alert

ACPI requires the correct HAL The only way you can use ACPI power management is if you have installed Windows XP Professional with a HAL that is ACPI-compliant. The HAL is detected during setup. If the wrong HAL was detected, you can replace it by reinstalling Windows XP. To verify which HAL was installed, right-click My Computer select Properties, and select the Hardware tab. Click the Device Manager button. In the right pane, click Computer. You should see Advanced Configuration and Power Interface (ACPI) PC listed under the computer if it is operating in ACPI mode.

A Group Policy refresh can prevent the computer from entering a low-power state because the computer notes the time that the last settings were applied, then resets the clock to 0 to start waiting for standby or hibernation. For example, assume a user has a Group Policy refresh interval of 45 minutes and your Power Options is set to enter hibernation after no activity of 60 minutes. The user goes to a meeting at 1:00 p.m. at the same time that the Group Policy is refreshed across the network, leaving the computer running. The Power Options is set to put the computer on standby at 2:00. However, at 2:45, the Group Policy is refreshed and Power Options is reset to put the computer on standby at 3:45 p.m. This cycle continues until the user returns and wonders why the computer hasn't gone into a low-power state. To ensure this doesn't happen, you can set the Power Options to a shorter time period than the Group Policy refresh interval.

To increase security, many companies require their computers to prompt for a password when a computer is awakened from a low-power state. This can be configured as a Group Policy and applied to a select group of users or all users in the Active Directory. To configure this policy, open the Group Policy Editor by clicking Start, Run, typing gpedit in the Open text box, and pressing Enter. In the Group Policy Editor, navigate under the User Configuration to Administrative Templates, System, Power Management. This is shown in Figure 7.14. A single GPO that you can edit appears in the right panePrompt for Password on Resume from Hibernate/Suspend. Double-click this GPO and select Enabled. Click OK to close the dialog box.

Figure 7.14. You can create a GPO that applies to power management.

Hibernation and standby differ somewhat. Where hibernation copies everything from RAM, saves it to the disk, then shuts down all components; standby continues to consume power to a minor extent to maintain RAM, but it also turns off the display, hard disk, network adapters, and other components. For a computer to go into hibernation, there must be enough free space to save the data that is stored in RAM. For example, a computer with 512MB RAM should have at least 512MB of free space on the disk for the computer to hibernate. This is not necessary for standby.

Administrators sometimes need to configure a computer to wake up when it receives a network request, either to provide remote management or to have the computer act as a print server. Wake-on support is not configured in the Power Options utility. It is an attribute of the device's properties, and only for certain devices such as modems and network adapters. To enable a device to wake the computer, you can right-click My Computer and select Properties. Click the Hardware tab, followed by the Device Manager button. In the Device Manager window, navigate to the devicein this example, the network adapterand double-click it. Click the Power Management tab. Select the Allow This Device to Bring the Computer Out of Standby check box. Click OK.