Video Hardware, Part 2 - Energy and Safety
(Page 2 of 10 )
Monitors, like virtually all power-consuming computer devices, have been designed to save energy for a number of years. Virtually all monitors sold in recent years have earned the Environmental Protection Agency's Energy Star logo by reducing their current draw to 30 watts or less when idle. Power-management features in the monitor, as well as controls provided in the system BIOS and in the latest versions of Windows, help monitors and other types of computing devices use less power.
For more information about power management, see Chapter 21, "Power Supply and Chassis/Case."
Power Management One of the first energy-saving standards for monitors was VESA's Display Power-Management Signaling (DPMS) spec, which defined the signals a computer sends to a monitor to indicate idle times. The computer or video card decides when to send these signals.
In Windows 9x/Me/2000/XP, you must enable this feature if you want to use it because it's turned off by default. To enable it in Windows 9x/Me, open the Display properties in the Control Panel, switch to the Screen Saver tab, and make sure the Energy Star Low-Power settings and Monitor Shutdown settings are checked. You can adjust how long the system remains idle before the monitor picture is blanked or the monitor shuts down completely. Use the Power icon in Windows 2000/XP to set power management for the monitor and other peripherals. You can also access power management by selecting the Screen Saver tab on the Display properties sheet and clicking the Power button.
Intel and Microsoft jointly developed the Advanced Power Management (APM) specification, which defines a BIOS-based interface between hardware that is capable of power-management functions and an operating system that implements power-management policies. In short, this means you can configure an OS such as Windows 9x to switch your monitor into a low-power mode after an interval of nonuse and even to shut it off entirely. For these actions to occur, however, the monitor, system BIOS, and operating system must all support the APM standard.
With Windows 98, Windows Me, Windows 2000, and Windows XP, Microsoft introduced a more comprehensive power-management method called Advanced Configuration and Power Interface (ACPI). ACPI also works with displays, hard drives, and other devices supported by APM and allows the computer to automatically turn peripherals, such as CD-ROMs, network cards, hard disk drives, and printers, on and off. It also enables the computer to turn consumer devices connected to the PC, such as VCRs, televisions, telephones, and stereos, on and off.
Although APM compatibility has been standard in common BIOSs for several years, a number of computers from major manufacturers required BIOS upgrades to add ACPI support when Windows 98 was introduced.
Note -ACPI support is installed on Windows 98, Windows Me, Windows 2000, and Windows XP computers only if an ACPI-compliant BIOS is present when either version of Windows is first installed. If an ACPI-compliant BIOS is installed after the initial Windows installation, it is ignored. Fortunately, both versions of Windows still support APM as well. See Microsoft's FAQ for ACPI on the Microsoft Web site.
Use Table 15.4 to select the most appropriate DPMS power-management setting(s) for your needs. Most recent systems enable you to select separate values for standby (which saves minimal amounts of power) and for monitor power-down (which saves more power but requires the user to wait several seconds for the monitor to power back up).
Table 15.4 Display Power Management Signaling State | Horizontal | Vertical | Video | Power Savings | Recovery Time |
On | Pulses | Pulses | Active | None | n/a |
Stand-By | No Pulses | Pulses | Blanked | Minimal | Short |
Suspend | Pulses | No Pulses | Blanked | Substantial | Longer |
Off | No Pulses | No Pulses | Blanked | Maximum | System Dependent |
Virtually all monitors with power management features meet the requirements of the United States EPA's Energy Star labeling program, which requires that monitor power usage be reduced to 15 watts or less in standby mode. However, some current monitors also comply with the far more stringent Energy 2000 (E2000) standard developed in Switzerland. E2000 requires that monitors use less than 5 watts when in standby mode.
 | This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738). Check it out at your favorite bookstore today. Buy this book now! |
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