What is hibernate?
Hibernation lets a PC power off completely without closing anything. Windows writes what is in memory, including open apps, documents and the system state, to the hidden file C:\hiberfil.sys, then cuts power. At the next power-on, Windows reads that file back into RAM and returns to the same session. In ACPI terms hibernation is S4, suspend to disk, compared with S3 sleep (suspend to RAM) and S5 soft off.
Hibernate vs. sleep vs. fast startup
| State | Where the session is kept | Power used while in it | Survives a dead battery |
|---|---|---|---|
| Sleep (standby) | RAM, which stays powered | A small, constant draw | No |
| Hibernate | hiberfil.sys on the system drive | None | Yes |
| Hybrid sleep | Both RAM and hiberfil.sys; used mainly on desktops | A small draw | Yes, it resumes from the file |
| Fast startup | Only the Windows system session, after users are signed out | None | Not applicable; it is a form of shutdown |
Sleep resumes in seconds; hibernate is slower because the saved memory must be read back from disk, though on an SSD the gap is small. Fast startup is why Shut down on a Windows PC is not a full cold boot: Windows hibernates its kernel session and reloads it at power-on. Restart always performs a full boot, which is why restarting, not shutting down, is the right advice after driver or update problems. Many newer laptops use Modern Standby instead of S3 sleep and can be set to move into hibernation after a period asleep.
Turning hibernation on and off
powercfg /hibernate onandpowercfg /hibernate off(short formpowercfg /h), run from an elevated prompt, enable or disable hibernation. Turning it off deletes hiberfil.sys, which can be several gigabytes because its size is based on installed RAM, and it also removes fast startup.- Windows 11 does not show Hibernate in the Start menu's power options by default. Add it in Control Panel > Power Options > Choose what the power buttons do > Change settings that are currently unavailable, then tick Hibernate under Shutdown settings.
- The same page sets what the power button, sleep button and, on laptops, closing the lid do, separately for On battery and Plugged in. Hibernate is one of the choices.
- In a power plan's advanced settings, Sleep > Hibernate after moves a sleeping PC into hibernation after a set time.
Troubleshooting
- Hibernate option is missing: hibernation is disabled, it has not been added to the power menu, or the hardware, firmware or virtual machine does not support it.
powercfg /alists the sleep states the PC supports and why others are unavailable. - The fast startup checkbox is missing: hibernation is off, and fast startup depends on it.
- Drive nearly full: hiberfil.sys is large. Disabling hibernation frees the space, at the cost of losing hibernate and fast startup.
- Laptop hot or flat after a trip in a bag: the lid action is Do nothing, or the PC woke from sleep. Set the lid action or a timer to Hibernate.
- Dual-boot file-system warnings: fast startup or hibernation left the Windows volumes in a saved state. Turn off fast startup before using the other OS.
Hibernate on the CompTIA A+ exam
Hibernate is one of the power settings in Core 2 (220-1202) objective 1.6. Know where the session is stored (hiberfil.sys on disk), that hibernation uses no power and survives a dead battery, how it differs from sleep and fast startup, and where Power Options sets lid and power-button actions. Cues: a traveling user must keep open work but use no battery, think hibernate; a short break with the fastest resume, think sleep; Hibernate or fast startup is missing from the options, think powercfg /h on and the power-button settings page.