Suspend (or Standby) mode is a light sleep mode that you can put your computer into. When you resume from the Suspend mode, you’ll be exactly where you left off – all your work will still be on the screen. While in Suspend mode, your computer needs a small amount of power to maintain it’s state. So for a laptop or desktop, if you’re plugged in to wall power, then you’re fine, but if you have a power failure, you may lose the Suspend mode and any unsaved work. Suspend mode should be considered a temporary state that you can place your computer in when you expect to be coming back to it within a few hours.
Hiberate mode is when your computer’s memory is actually written out to disk just before powering off and stays there until you turn the computer back on. When the computer comes back on, it’s exactly the way you left it. A computer can stay in hibernation mode for a much longer period of time than Suspend mode when unplugged, and it uses less electricity. It takes slightly longer to resume from Hibernation mode than from Suspend mode. However, it is more secure from a data integrity viewpoint because everything is written out to disk.
From a technical viewpoint, Suspend and Hibernate are defined by two of the global states defined in the ACPI specification.
- S3 – Suspend (to RAM), Standby, Sleep. Power is required to maintain RAM state.
- S4 – Hibernation or Suspend to Disk. All content of main memory is saved to non-volatile memory such as a hard drive, and the computer is powered down.
By the way, not all computers have the capability to hibernate correctly.