What is hiberfil.sys?
hiberfil.sys is a hidden system file located in the root of your C: drive. Windows uses it to store the contents of your RAM when your PC enters hibernation mode or uses Fast Startup.
Why Does It Exist?
It serves two purposes:
- Hibernation: Saves your entire session (open apps, documents) to disk so your PC can fully power off and resume exactly where you left off
- Fast Startup (Windows 10/11): A hybrid shutdown that saves the kernel session to speed up boot time
Can You Delete It?
⚠️ Use caution, you can remove it, but:
- You’ll lose hibernation functionality
- Fast Startup will be disabled (slightly slower boot times)
- On laptops, you lose the ability to hibernate when battery is critically low
How to Delete hiberfil.sys
You can’t delete it directly. You must disable hibernation via Command Prompt:
- Open Command Prompt as Administrator
- Run:
powercfg -h off - The file is automatically deleted
To re-enable later: powercfg -h on
What Happens If You Delete It?
- Hibernation is completely disabled
- Fast Startup is disabled (boot may be 2–5 seconds slower)
- You free up 2–8 GB of space (proportional to your RAM)
- No risk of data loss or system instability
Bottom Line
If you never use hibernation and have an SSD (where Fast Startup makes minimal difference), disabling it is a reasonable trade-off for the disk space savings.
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