Preface
Windows relies on several hidden system files to deliver smooth user experiences, especially when managing power states. One of the most important among them is hiberfil.sys, a file directly tied to the operating system’s Hibernate and Fast Startup features. Although it typically remains invisible to everyday users, knowing its purpose can help you manage disk space, optimize system behavior, and troubleshoot power-related issues.
What Is hiberfil.sys?
hiberfil.sys is a system file used by Windows to store the contents of your system’s memory (RAM) when the machine enters Hibernate mode. During hibernation, Windows saves the entire memory state—including open documents, running applications, and system context—to this file before shutting down. When the system powers back on, it restores the saved data and resumes exactly where you left off.
This file is also required for Fast Startup, a hybrid shutdown mode introduced in modern Windows versions to accelerate boot times.
Where Is It Located?
hiberfil.sys is stored in the root directory of the system drive:
C:\hiberfil.sys
It is hidden and protected by the operating system and cannot be opened or edited directly.
Why Does hiberfil.sys Take So Much Space?
The size of hiberfil.sys is typically 40–100% of your installed RAM, depending on system configuration. For example, a PC with 16 GB of RAM may have a hibernation file between 6–16 GB.
The reason is simple: the file must be large enough to save the system’s memory contents, although Windows uses compression to reduce storage requirements.
How Windows Uses the File
Windows relies on hiberfil.sys in two scenarios:
1. Hibernate
- Saves the full memory snapshot to disk
- Powers off the system
- Restores everything on the next boot
Hibernate is ideal for users who want to continue work later without consuming power.
2. Fast Startup
- Saves a partial memory snapshot, mostly kernel and driver data
- Speeds up boot time
- Requires
hiberfil.systo function
Disabling the file also disables Fast Startup.
Can You Remove or Resize hiberfil.sys?
Windows does not allow manual deletion. However, you can disable or adjust it via built-in commands.
Important: Run the following commands in an elevated Command Prompt (Run as Administrator).
Disable Hibernate (and remove the file)
If you do not use Hibernate or Fast Startup:
powercfg /hibernate off
This removes hiberfil.sys automatically.
Re-enable Hibernate
powercfg /hibernate on
Resize the File (for Fast Startup only)
You can reduce its size while keeping Fast Startup:
powercfg /hibernate /type reduced
This creates a smaller hibernation file used only for kernel memory.
Restore the Default File Size
powercfg /hibernate /type full
When Should You Disable hiberfil.sys?
You may consider disabling hibernation if:
- You need to free several gigabytes of disk space
- You never use Hibernate mode
- You do not rely on Fast Startup
- You are optimizing a virtual machine image
However, keep in mind that disabling it will remove convenience features and may slightly increase boot times.
Best Practices
- Keep it enabled if you frequently use hibernation or Fast Startup.
- Resize instead of removing if you only want Fast Startup.
- Avoid manual file deletion; always use
powercfgcommands. - Ensure sufficient disk space on systems that rely on Hibernate for workflow continuity.
Conclusion
hiberfil.sys is a crucial component of Windows power management. While it may occupy a significant amount of disk space, it enables fast booting and seamless session restoration. Understanding how it works—and knowing how to control it—allows you to tailor your Windows experience to your performance, power, and storage needs.