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Sleep, hibernate and Fast Startup: three switches people confuse

Verified 2 min read

What each power state does, what Fast Startup actually writes to disk, and why it breaks dual boot and update troubleshooting.

Tested onPro (26H2) / Server · Build 26300.9457 / 26100.33650 · x64
E1
Build
26300.9457 / 26100.33650
Edition
Pro (26H2) / Server
Architecture
x64
Support
Documentation (E1)
Evidence
E1Official documentation
Verified
2026-10-29
Page type
Concept

The short answer

Section titled “The short answer”

Three different things:

Feature State RAM kept powered Writes to disk
Sleep (S3) suspend to RAM yes no
Hibernate (S4) suspend to disk no hiberfil.sys
Fast Startup hybrid shutdown no partial hiberfil.sys

Sleep is instant and fragile (battery drain). Hibernate is slow to resume and survives power loss. Fast Startup is not sleep at all — it is a shutdown that keeps the kernel session on disk.

Check what the machine supports

Section titled “Check what the machine supports”
Terminal window
powercfg /a

Typical output on a Modern Standby laptop:

待机 (S0 低电量待机)
休眠
快速启动

On a desktop:

待机 (S3)
休眠
快速启动

If 休眠 is missing, hiberfil.sys is disabled (powercfg /hibernate off) or the disk is too small.

Fast Startup: what it really does

Section titled “Fast Startup: what it really does”

On shutdown with Fast Startup enabled:

  1. User sessions close (that part is a real logoff).
  2. The kernel session is hibernated to hiberfil.sys.
  3. Next “boot” resumes that image instead of initialising drivers from scratch.

Consequences people hit:

  • Updates that need a full restart may not fully apply until a real restart (shutdown /s /full or Restart).
  • Dual boot: the hibernated image keeps NTFS mounted; Linux may refuse to mount or mount read-only.
  • Driver changes may not take effect on “shutdown then start”.
  • Troubleshooting a boot problem is harder because the boot is not a boot.
Terminal window
# is Fast Startup on? (1 = enabled)
Get-ItemProperty 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Power' -Name HiberbootEnabled
# a real, full shutdown
shutdown /s /full /t 0

Hibernate: the honest trade

Section titled “Hibernate: the honest trade”

Hibernate writes RAM content to disk and powers off. Resume reads it back.

  • Pro: survives power loss, zero battery drain, resumes your session.
  • Con: resume time proportional to RAM and disk speed; hiberfil.sys is roughly 40% of RAM by default.
Terminal window
powercfg /hibernate on
powercfg /hibernate size 60     # percent of RAM
powercfg /hibernate off         # deletes the file, disables fast startup too

The file sits at C:\hiberfil.sys and is not visible in Explorer without showing protected OS files.

Which to use

Section titled “Which to use”
Machine Recommendation
Desktop, always plugged in Sleep on, hibernate optional, Fast Startup off if you dual boot
Laptop, Modern Standby Let the OEM defaults stand; add hibernate as a battery safety net
Dual boot with Linux Fast Startup off, hibernate off for the Windows volume
Server Sleep off; hibernate usually off
Troubleshooting boot issues Fast Startup off until resolved

Sleep that drains the battery

Section titled “Sleep that drains the battery”

If the machine loses power in sleep (laptops with Modern Standby), see Modern Standby for the powercfg /sleepstudy method. That is a different failure mode from hibernate.

Section titled “Related”

Lab boundary

Section titled “Lab boundary”

E1. Power states and Fast Startup behaviour are documented by Microsoft. The lab VMs expose no real sleep/hibernate path, so no resume timings are published.

Sources