sleep mode v. hibernate mode
Friday, November 12, 2010 
Image courtesy of PantherKut.com. Sleep and hibernate are power saving states for computers and other electronic devices.
In sleep mode, also known as stand by or suspend, the computer uses much less power than it does when running normally. This is done by saving the state of open programs and documents to RAM (memory), reducing the RAM refresh rate, turning off the monitor, cutting power to the CPU, spinning down the hard drive(s), and placing the power supply in a reduced power mode. Sleep mode can be entered after a defined period of inactivity, when a button is pressed, or on laptops, when the lid is closed. Under the Advanced Configuration and Power Interface (ACPI) standard, sleep mode is state S3.
In hibernate mode, the entire system state (the contents of the RAM) is saved to the hard drive, and the system powers down. Hibernation is most often used in mobile computers, where battery life and complete loss of power are significant concerns. Hibernation is ACPI state S4.
- Sleep consumes perhaps a tenth as much power as running normally; hibernation is equivalent to the computer being turned off, and drains almost no power.
- Waking from sleep can take as little as a few seconds. While waking from hibernation takes less time than a cold boot, it can still take several minutes.
- In the event of power loss, a sleeping computer will lose all of the data in memory, such as unsaved documents. A hibernating computer will be unaffected by loss of power.