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Are you sleeping? Understanding hibernation, standby, and other power management features

All over the world, users are banging their power buttons and cursing because they don't understand new power management features. In this Daily Feature, Mike Jackman helps you help them.


These days, computers have more advanced power management features than their predecessors. If you’ve ever seen your users banging on the power button, not understanding why their computers won’t wake up, you’ve seen the fruits of the latest power management in action—or inaction, as the case may be. In this Daily Feature, I’ll give an overview of power management and discuss commonly misunderstood power management features so you can help your users reduce their frustration.

Blame ACPI
Power management has added a new level of perplexity for end users, who have enough to worry about as it is. The culprit is a standard called ACPI, or Advanced Configuration and Power Interface. Introduced in 1997 by Intel, Toshiba, and Microsoft, ACPI’s goal was to take control of power management away from the BIOS and place it in the OS. Windows 98 and 2000 both support ACPI, but Windows NT doesn’t natively support it, though many computer manufacturers have add-ons that support most features.

While the operating system decides when to implement different levels of power management under ACPI, it can’t do the job without an ACPI BIOS. An ACPI-capable BIOS knows how to implement it. The BIOS contains tables listing various power states for devices. The power states include: enabled, standby, suspend, off, and various levels of “sleep.” If Windows 2000 decides to put the system into standby, it will make the request to the BIOS. The BIOS then sends a signal to each device to put it in a low-power state. The BIOS table would list the proper signal to send to the NIC, for example, for the best low-power state it could be in. When the system powered back on, the BIOS would send a wake-up call to the NIC. To create its table, the BIOS gets its power information from each device the same way it does for other hardware configuration info—through Plug and Play.

The actual performance of ACPI is far from ideal. Microsoft’s Knowledge Base contains many articles describing problems that occur due to devices and software interfering with the smooth operation of suspend and hibernation. Most of these issues have to do with problems coming back from standby. But overall, ACPI is a useful tool for extending battery life and using computers in environmentally friendly ways. As for your users, it causes a great deal of frustration.

You can read all you’d ever want to know about ACPI in the Advanced Configuration and Power Interface Specification, created by Compaq, Intel, Microsoft, Phoenix Technologies, and Toshiba.

To sleep, perchance, to hibernate?
Your users’ most misunderstood ACPI features are encountered most often on laptops, and they include standby (also called sleep), suspend (again, also called sleep), and hibernation. It doesn’t help that in reality, sleep, standby, and suspend are often used interchangeably. In fact, standby mode in Windows 98 is called suspend mode in Windows 95, Windows NT, 2000, and the Phoenix BIOS!

Whatever their names, all these modes have two goals: to reduce power use by your computer and all its devices and to let you keep the desktop as you left it, with all your open programs and documents in progress.

If the goal were simply to conserve power, turning off your computer would do the trick. But then you’d have to first close all your programs and documents. When you rebooted the system, you’d have to open them up again. By that time, you would have wasted a lot of your power savings getting the system back up to speed. Therefore, it’s the second goal that makes these features valuable.

Think of your computer in standby and suspend modes as if it were taking a catnap, a light sleep from which it can wake up fairly easily. On some systems, suspend can be a deeper nap than standby. It takes a little longer to come back (the time a device takes to wake up is known as latency), and it expends less energy while napping. Hibernation, as the name implies, is an even deeper level of unconsciousness. As far as device operation is concerned, the essential differences between the power-saving modes are these: Standby and suspend modes tell your computer to:
  • Switch to a low-power state.
  • Turn off devices, such as the monitor or LCD screen, and hard disks.

The differences will be in degree.

Hibernation mode tells your computer to:
  • Write everything in RAM to disk.
  • Turn off the monitor and hard disk.
  • Turn the computer off.

While suspend may turn off the screen, reduce CPU power consumption, and turn off some devices, standby mode usually puts all devices in a low-power state, and only keeps system memory refreshed and the CPU idling. Therefore, the computer wakes up more slowly than when in suspend. Hibernation mode is essentially switching off the computer, except it is able to restore the OS by reading back into memory the contents of the file it wrote before going into hibernation. In all three cases, when the computer wakes up, the desktop should look the same as it did before.

Why your users are banging on the power button
Because these modes are implemented differently, depending on the hardware your users have, on the OS installed, on default values, and on user settings, users are confused. In a nutshell, even the simple power button is not so simple any more. New advanced power management means that users can change the role of the power button. It can be set to:
  • Shut down the computer.
  • Switch to standby or suspend.
  • Turn the computer on or wake it up from any mode.

That’s why computer users with new equipment get frustrated—no matter what mode the computer is in, it seems like it’s off. So they press the power button. On some equipment, the hard drive activity light comes on; on others, the power light greens and the POST test starts. On still other equipment, the computer seems to just hang while it’s is waking up from hibernation, as power comes on and drive activity signals that the saved information is being read into memory.

Complicating matters further, some computers have two power buttons, and some have only one. Those with two buttons are often marked with icons that make no sense to anyone. On laptops, the true power button (the one that will turn the computer completely off and cause the OS to report that it shut down unexpectedly last time) is often a slider switch. Its icon is a circle with a dot at the top. The “other” power button is a simple push model, often marked with a circle containing a short vertical line at the top. When the computer’s on, you can push the power saving button once and the machine may beep, then go into either standby, suspend, or hibernation. Hold the button down for a few seconds and it may shut off (or it may not). Push the button again and it will return from whatever mode you put it in. If it takes too long, users will push the button again and again. Then they’ll try the other button. Eventually, they’ll just turn the machine off, losing whatever work they had saved and causing a recovery reboot, complete with hard disk diagnostics. They may even crash the OS for good. Since both buttons can turn the computer on, they seem to work the same way. See why your users are confused?

Manually setting power use
My recommendation is simple. Configure all power buttons so that they do the one job all users understand: turn the computer off/turn the computer on. If you can’t change two-button computers, explain the differences between the buttons immediately upon issuing the laptop. Then educate users to configure power management options through the control panel.

Figure A shows a typical menu for configuring power settings. Your menu will differ depending on OS and third-party or OEM add-ons. This example comes from Windows 2000. In this case, the Power Options Properties dialog is opened to the Advanced tab, showing how a user can set the power button to either power off the computer or put the computer in standby mode.

Figure A
Windows 2000 lets users set the role of the computer’s power switch.


Figure B shows another example of power settings. In this case, the operating system is Windows 98, the dialog box is called Power Management Properties, and extra tabs are available for options added by Compaq. The Power Schemes tab allows users to choose from preconfigured settings or to make their own custom settings and save them under a unique name. In this example, when the computer is plugged in, it will go to standby after two hours. (Note that the mode is not called suspend in Windows 98.) When it’s running on batteries, it will go to standby after two minutes. Users can also adjust the power off times for monitors and hard disks.

Figure B
Users have a variety of preset power schemes available, or they can make their own. Note that in Windows 98, the mode is called standby, not suspend.


Conclusion
ACPI support in the BIOS and in Windows operating systems allows computers to conserve energy and to run longer when using batteries. Wear and tear on the CPU is reduced, as well, leading to longer CPU life. However, the options made possible by ACPI cause a lot of end-user frustration, as evidenced by people banging on their power buttons and cursing. If you teach users the options they have available and educate them to the new roles for power switches, you will do a lot to ease their frustration. They’ll be able to stand by calmly while the computer powers on and not be in suspense every time they hit a power button.
The authors and editors have taken care in preparation of the content contained herein but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.

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