To conserve power when not using the computer, you generally have 3 options: shut down, hibernate or sleep. The state of open documents and applications running is preserved when sleep or hibernate modes are used. However, booting up is faster from sleep than from hibernate because contents of the RAM are preserved. Hibernate uses less power than sleep because contents of the RAM do not need to be preserved; they are saved on the hard disk. Hibernation is similar to regular shutdown but without the unnecessary hassle of terminating all open applications.
|Processing Functions||Closed and saved to hard-disk||Stopped and saved in RAM|
|Power usage||Zero power||Low power consumption|
|When to use||When the system is idle for longer time and rebooting after shut down will be tiresome or inconvenient.||When the system is idle for a short time|
|Operating Systems supported||All OS where the hardware is ACPI enabled including Windows, Mac OS X and Linux||All OS where the hardware is ACPI enabled including Windows, Mac OS X and Linux|
|Also known as||Suspend to disk (Linux), Safe Sleep (Mac), S4 in ACPI||Standby (older versions of Windows), Suspend to RAM (Linux), S3 in ACPI|
State of the computer
The state of the computer upon resumption is the same before it enters hibernate or sleep mode.
During hibernation, the hardware is completely powered down while the computer retains its state. Similar to shut down, a hibernating system needs more time to start up. On start-up, data is read back to the RAM which takes about 10 seconds or more. Hibernation provides the advantage of eliminating the need to save data before shutting down and restore the applications on power up.
During sleep mode the computer cut power to subsystems that are not needed and places RAM into minimum power state. As a result the resumption on waking up is instantaneous. Only the CPU and the display need to be powered up. Most laptops enter this mode when the machine is running on batteries and is closed.
Pros and Cons
- Risk of data loss: Higher in sleep mode. During hibernation, data is automatically stored in a non-volatile memory before the hardware shuts down. In sleep mode, the data is still in the RAM, which is volatile. In case of a power outage, any unsaved data is lost and cannot be recovered.
- Time to resume: Faster in sleep mode. In sleep mode, since the data is stored in RAM, the resumption is immediate and no time is lost. But a hibernating system needs comparatively more time to resume as it needs time to read back the data from the hard disk or other permanent memory storage.
- Power consumption: Lower in hibernate mode. A hibernating system uses no power at all while a system in sleep mode consumes small but continuous power.
A speed test of switching from sleep/hibernate mode to resume mode is performed in this video:
Operating system support
Hibernate and Sleep modes are supported in all operating systems where ACPI is supported. Hibernate is defined as S4 in ACPI and sleep as S3.
Some of the options available for Hibernate and Sleep in various OS are:
|Operating System||Hibernate Mode||Sleep Mode|
|Windows|| Hibernate - available since Windows 2000 |
Hybrid Sleep - introduced in Windows 7
Hybrid Boot - introduced in Windows 8
|Suspend - Windows 95 |
Standby - Windows 98 - 2003
Sleep - Windows Vista and later versions
|Mac OS X||Safe Sleep||Sleep|
|Linux||Suspend-to-disk option||Suspend or suspend-to-ram option|
Hybrid Sleep mode is a mix of sleep mode and hibernate, where the contents are stored in RAM and hard drive. The RAM stays powered during power down. The restart is faster (contents retrieved from RAM) and with minimal power loss. During a complete power loss (power outage scenario), when RAM is offline, data is retrieved from the hard drive.
Hybrid Boot mode where the user is logged out before hibernating, thereby drastically reducing the size of the hibernation. It hence takes less time to write to disk and resume.
In the Advanced Configuration and Power Interface (ACPI) specification, hibernation is called suspend-to-disk and is the S4 power state in the standard. And sleep (also called standby or suspend-to-RAM) is the S3 power state.