Stand-by, Sleep, and Hibernation in Microsoft Windows
Introduction
Going all the way back to Windows 95, you may have seen options in the Control Panel or in the shutdown menu about suspend, stand-by, sleep, or hibernation for your computer, as opposed to just an ordinary shut down. These are power-saving modes that were developed to save your laptop battery, or just save energy in general, without having to close any of your programs or shut down Windows. All other computers, such as iMac desktops or MacBook laptops running Mac OS X, and computers running UNIX-like operating systems (Red Hat, CentOS, Fedora, Debian, Ubuntu, FreeBSD, etc.) support similar functions. This article covers Microsoft Windows only.
Sleep / Stand-by / Suspend / Hibernate
Despite the disparate terminology, there are only two modes involved here. There are:
Sleep / Stand-by / Suspend
In this mode, your computer turns off everything except limited control electronics on the main system circuit board (motherboard), and your system working memory (RAM). All programs and documents stay open in RAM, but anything the computer was doing is suspended (such as a file download). Your screen turns off, the hard drive spins down, and most peripherals are disconnected. The computer draws only enough power to maintain this state, and to detect a keyboard button press or mouse movement to wake up the computer and resume normal operations. If you leave a laptop in this state for too long and the battery drains, the computer may simply shut off, and you might lose work you had not saved, because working memory (RAM) always needs continuous electricity. The same thing will happen if you have a desktop computer in sleep mode (without any kind of supporting battery), and the power goes out or the computer is unplugged. In some cases, your computer may detect when it's about to lose power while in sleep mode, and it will hibernate itself to avoid losing your saved state.
Many computers go to sleep by themselves after a period of inactivity. When you are away from your computer and you have to wiggle the mouse to wake it up, and you hear the fans and hard drives spinning up from being off, this is your computer coming out of sleep mode.
For a while, it was common for laptops, and even keyboards for desktop computers, to have a button or key with a moon-shaped icon, which would signal the computer to go to sleep mode. Laptops typically go into sleep mode when you close the lid as well.
Sleep mode is supported in Windows 95 and later (depending on your computer hardware), except for Windows NT 4.0 (1996). Windows 2000 Professional supported it on laptops only. Although it went by different names over the years, it is functionally the same.
| Windows Version | Term Used |
|---|---|
 Windows 95 | Suspend |
Windows 98 through  Windows XP | Stand by |
 Windows Vista through  Windows 10 | Sleep |
Hibernation
Designed primarily for laptops, hibernation involves the computer saving the entire contents of your computer's working memory (RAM) to a file on your hard drive, enabling the computer to turn off completely. It requires no electricity to maintain this state. All programs and documents you had open will be imaged in the hibernation file exactly as they were in RAM. This does, however, require enough free space on your hard drive to save the contents of RAM, which isn't typically a problem on modern computers. When you turn your computer back on, Windows will see that there is a hibernation file, and it will copy that into RAM and resume operations.
Hibernation is supported in Windows Me (1999) and later, including Windows 2000 Professional. The earlier Windows 95 and Windows 98 supported it only if the computer manufacturer provided hardware-specific software drivers, and it may have gone by other names, such as suspend-to-disk. Prior to Windows XP (2001), hibernation made a file as large as your system RAM. Windows XP and later support compressing the contents of your working memory to make a smaller hibernation file for better performance. The hibernation option is usually not available by default; to see the option to hibernate in the shut down menu, you will need to enable it in the Control Panel.
More Options
Windows Vista (2007) introduced hybrid sleep, which combines the best of sleep mode and hibernation. When you put your computer to sleep, Windows Vista and later saves the contents of your RAM as if it's going to hibernate, then goes into sleep mode, maintaining what's in RAM as well. When you wake up your computer, it will resume operations immediately from RAM and delete the hibernation file; if your computer happened to lose power or the battery died while it was asleep, then it can restore what was in RAM from the hibernation file. Hybrid sleep is on by default, which explains why you do not see the option to hibernate in the shut down menu any more in Windows Vista and later. If you disable hybrid sleep in the Control Panel, you will then see the option for a full hibernation alongside the sleep option, which will now behave as it did in prior versions of Windows.
Common Problems
Waking up from sleep mode has always been a problem, although with better coordination between hardware makers and Microsoft, it is less of a problem than in years past. Some peripheral devices or software programs would get confused when your computer woke up from sleep mode, causing unpredictable behavior. It was not uncommon to find that, after putting a laptop to sleep, you couldn't wake it up at all, requiring you to hold the power button down for four seconds to shut it off and start it up again, losing whatever you had open that was not saved.
The network hardware in most computers is designed to listen on the network for any inbound messages the computer might need to wake up for, but this has also often been unreliable. For this reason, on managed networks, system administrators may need to install separate hardware management software that wakes up the workstations on a schedule so they can do remote maintenance on them at night or on weekends (such as installing new applications or software updates), and not have to hope the computer wakes up from sleep mode in response to a management request over the network. Or, some administrators simply choose to configure all computers to stay on all the time to simplify management, at the cost of a slightly higher electric bill.
What to Choose?
As you've seen already, there are many trade-offs among the various options for saving power on your computer. The one that works best for you depends on your goals, your usage patterns, and your computer's capability. Now that you have a better understanding of how each mode works, you can experiment with your equipment to see if you can find a better way of managing your power.
If you're adventurous, you might have already found yourself in the power options applet of the Control Panel, looking at an array of items you can finely control, such as when the hard disk spins down or your monitor turns off (note that the monitor turning off is different from a screen saver, which is a pattern of graphics designed to prevent the same image from displaying so long on your screen that it burns in to your monitor). These are some things you might want to do if you don't want to use sleep mode, but you're still concerned about electricity use, either to save money on your bill or conserve a laptop battery that doesn't seem to last very long. If you set these options, Windows will manually control spinning down your hard drive or turning off your monitor, while your computer and all other peripherals will remain fully online and awake. This can allow you to save some energy, while avoiding the instability that can be caused by sleep mode.