Sleep Mode Warning

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If power is lost while in sleep mode, it is the same as pulling the plug while using the machine. Everything stored in RAM is lost and files in process of writing to the disk may become corrupted.

4. Standby - The machine has been powered "off" by the operator. Power is withdrawn from the CPU, RAM, disk drive, and other components. The computer continues to draw less than 2 watts of power for as long as it is plugged into the electrical outlet. Part of this power is used to operate the network card at low power as it listens for the Wake On LAN signal. The best way to cut even this small flow of electricity is to plug the unit into a power strip and turn off the power strip.

5. Hard Off - A device that is not receiving any electrical power at all. This may be the result of physically unplugging it from an outlet or connecting to the power source through a power strip that has been turned off.

Network Controlled Power Management addresses one of the significant objections to deenergizing computers. Most companies push software patches and antivirus updates to company machines after normal working hours. This minimizes disruption to the operators and allows plenty of time for long downloads and mandatory restarts. ENERGY STAR certified computers do not lose their network connection when in a low power (Standby) state.

Network Controlled Power Management includes the hardware and software that connects the computer to the organization's network. This is the network card, connection, driver software for the card, and so on.

▲ Wake Event - Moving a device from stand-by or sleep to powered mode. This is the receipt of a signal over the network to wake up.

▲ Wake On LAN - A capability of the computer to return to a fully powered state from a Sleep or Standby state on receipt of the proper command. This requires that the unit's network security configuration is set to permit Wake On LAN. Usually this is a combination of an operating system setting and a logical switch in the hardware.

▲ While in Standby mode, the computer listens on the network connection for a command to wake up, known as a "magic packet." This signal is sent on a LAN's broadcast address and uses port 0, 7, or 9. The computer examines the packet to see if holds its MAC address (actual format is hexadecimal FF 6 times followed by the target unit's MAC address repeated 16 times). If the NIC uses password protection for this feature, then it is appended to the packet.

Computers shipped to commercial customers must be set for Wake On LAN. Units shipped to consumers should have this capability turned off. However, Windows users can activate this through the network device's properties under the Device Manager.

Companies that use Microsoft's Active Directory supporting Windows XP operating system can download a free utility for controlling workstation power management. "EZ GPO" enables power management using Group Policy Objects (GPOs). Windows Vista already has this function and an extra utility program is not required. EZ GPO is offered as open source and does not charge licensing fees. p — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — — ^


Computer Power Management requirements are sometimes adjusted to address how people use the technology. Some use their computers for Voice Over IP (VOIP) to provide telephone service.

This saves on long distance charges. However, what happens if the computer is in sleep or standby mode when a call comes in? In 2008, Intel introduced a Remote Wake capability on its motherboards so when a call is received, the computer is moved from standby or sleep mode to full operation.


Computer monitors have come a long way. From modified televisions displaying text and basic graphics they have evolved into devices with the ability to display an infinite number of colors with great clarity. However, monitors have always been significant consumers of electricity. The high energy usage of monitors was one of ENERGY STAR's original challenges.

Older monitors used cathode ray tubes (picture tubes) to display images. This technology requires high voltages to paint the picture on the screen. A 17-inch display might require 70 watts or more of power under normal use. Since the display was operational as long as the computer was running, this amounted to a lot of electricity. Screen saver software was popular to prevent the same image from burning into the screen of a computer that sat idle over time. Unfortunately, running a screen saver program is the same as running a computer and its monitor for other tasks, so the unit consumed as much electricity as if it was performing useful work.

Most monitor manufacturers today use liquid crystal technology to display information. In full operation, these monitors consume about one-third as much power as a CRT-based device. However, to be ENERGY STAR compliant, they must also switch to sleep mode if they are idle for more than 15 minutes. Turning a monitor off and on multiple times a day will not hurt it. The voltage surge from a "power on" only wears on the components a small amount. The cumulative effect would take many more years to become apparent than the device will be in service.

Monitors seeking an ENERGY STAR rating must meet three criteria:

1. Power on mode (displaying an image) - The maximum power allowed for ENERGY STAR certification is 28 times the number of megapixels. So if the display resolution was rated at 1280 by 1024, the maximum allowed power would be 1.31 megapixels multiplied by 28 watts or 37 watts.

2. Sleep mode (i.e., a blank screen that is initiated by a command from the computer) uses 2 watts or less. The monitor returns to full operation on command from the computer. Manufacturers must ship monitors with a switch setting for the monitor to change to sleep mode if idle for 30 minutes. However, the device's operator may change this setting as desired, such as for a monitor that must always display the status of a particular operation. Monitor sleep mode is controlled by both the computer and the internal monitor logic. The monitor may act independently of the computer to enter sleep mode. However, its wake up comes from the computer's operating system.

3. Off mode - When the user has turned the power switch off, the monitor cannot use more than 1 watt of power. To ensure a monitor is completely powered off, it must be plugged into a power strip that is turned off to stop the flow of all electricity to the device. The ENERGY STAR program requirements for computer monitors version 4.1 refer to this as "Hard Off" mode.

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