Why the Hibernate File Survives a Reboot and Slows Cold Start in Windows 11

You restart Windows 11 expecting a clean boot, but the system still feels sluggish and takes longer to start than expected. The hibernate file, hiberfil.sys, is the cause. It survives a standard reboot because Windows 11 uses Fast Startup, which saves a copy of the kernel and drivers to the hibernate file during shutdown. This article explains why the hibernate file persists across reboots, how it slows cold start performance, and how to disable Fast Startup to regain full shutdown and boot speed.

Why the Hibernate File Survives a Reboot in Windows 11

The hibernate file, hiberfil.sys, is a system file that stores the current state of the operating system kernel, loaded drivers, and running applications before the computer enters a low-power state. Windows 11 uses this file for two features: Hibernate mode and Fast Startup. When you choose Shut down, Windows 11 does not perform a full shutdown by default. Instead, it logs off all user sessions and then saves the kernel session to the hibernate file. On the next power-on, Windows reads this file to restore the kernel and drivers quickly, bypassing the full initialization sequence. This process is called Fast Startup.

During a standard reboot, Windows 11 follows the same path. It logs off user sessions, saves the kernel state to hiberfil.sys, and then restarts the system. When the system comes back online, it loads the saved kernel from the hibernate file. The hibernate file is not deleted or rewritten with a fresh kernel state during a reboot. It persists with the same data, which can include stale driver states, cached memory pages, and other system data that is not refreshed.

The persistence of the hibernate file across reboots means that a cold start, where the system is fully powered off and then turned on, does not occur unless Fast Startup is disabled. A true cold start requires the system to initialize hardware, enumerate devices, and load the kernel from scratch. When the hibernate file is present and loaded, the system skips these steps, which can mask hardware issues, driver updates, or memory changes. Over time, the hibernate file can grow to 40% to 75% of the total RAM size, and loading a large file from disk delays the boot process, especially on systems with a mechanical hard drive or a slow SSD.

Steps to Disable Fast Startup and Remove the Hibernate File

To stop the hibernate file from surviving a reboot and slowing cold start, you need to disable Fast Startup and optionally delete the hibernate file. Follow these steps in order.

Disable Fast Startup Through Control Panel

1. Open Power Options
   Press Windows key + R, type control, and press Enter. In Control Panel, set View by to Large icons. Click Power Options.
2. Access the Fast Startup toggle
   In the left pane, click Choose what the power buttons do. At the top of the next screen, click Change settings that are currently unavailable. You need administrator privileges for this step.
3. Uncheck Turn on fast startup
   Under Shutdown settings, uncheck the box labeled Turn on fast startup (recommended). Click Save changes. This setting disables the use of the hibernate file during shutdown and reboot.

Delete the Hibernate File Using Command Prompt

1. Open Command Prompt as administrator
   Press Windows key, type cmd, right-click Command Prompt, and select Run as administrator. Click Yes in the User Account Control prompt.
2. Run the powercfg command to disable hibernate
   Type powercfg /h off and press Enter. This command deletes the hiberfil.sys file immediately and disables both Hibernate mode and Fast Startup. The file is removed from the root of the C drive.
3. Verify the hibernate file is removed
   Open File Explorer, go to the C drive root, and check that hiberfil.sys is no longer visible. If you have hidden system files enabled, you will see the file is gone.

Re-enable Hibernate Without Fast Startup (Optional)

If you still want to use Hibernate mode but not Fast Startup, you can re-enable hibernate with a different command. Open Command Prompt as administrator and run powercfg /h /type full. This creates a new hiberfil.sys file for Hibernate mode only. Then go back to Power Options and ensure Turn on fast startup remains unchecked. The hibernate file will now be used only when you select Hibernate from the Power menu. It will not be loaded during a normal shutdown or reboot.

If Windows 11 Still Slows Down After Disabling Fast Startup

Cold Start Is Still Slow After Disabling Fast Startup

If disabling Fast Startup does not improve boot speed, the slow start may be caused by other factors. Check for too many startup applications. Open Task Manager with Ctrl + Shift + Escape, go to the Startup tab, and disable any programs that are not essential. Also check if your system drive is nearly full. Windows 11 needs at least 20% free space on the system drive for virtual memory and temporary files. A fragmented hard drive can also slow boot. Use the defragmentation tool by typing defrag in the Start menu and optimizing the C drive.

Hibernate File Reappears After a Windows Update

Some Windows 11 updates may re-enable Fast Startup or recreate the hibernate file. After a major update, check the Fast Startup setting in Control Panel. If it is checked again, uncheck it and run powercfg /h off from an elevated Command Prompt. To prevent automatic re-enablement, you can set a Group Policy to disable Fast Startup. Press Windows key + R, type gpedit.msc, and navigate to Computer Configuration > Administrative Templates > System > Shutdown. Double-click Require use of fast startup, set it to Disabled, and click OK.

Battery Drain Increases After Removing Hibernate File

Without the hibernate file, your laptop will not have Hibernate mode as a power-saving option. If you close the lid or leave the laptop idle for a long time, it will enter Sleep mode instead. Sleep uses more battery than Hibernate because it keeps RAM powered. If you need Hibernate for battery conservation, re-enable it with powercfg /h /type full but keep Fast Startup disabled. The hibernate file will be used only when you explicitly choose Hibernate from the Power menu.

Fast Startup vs Full Shutdown: Boot Behavior and File Persistence

Item	Fast Startup Enabled	Full Shutdown (Fast Startup Off)
Kernel initialization	Kernel loaded from hiberfil.sys	Kernel loaded from scratch
Hibernate file persistence	File survives shutdown and reboot	File is not used during shutdown; deleted if hibernate is off
Boot time	Faster on warm boots, slower on cold starts due to file read	Slower on first boot, consistent performance over time
Driver and hardware changes	May not detect new hardware until a full restart	Detects all hardware changes on each boot
Disk space used by hiberfil.sys	40-75% of RAM size	0 bytes if hibernate is disabled
Power consumption during shutdown	Low, but system is not fully off	Zero, system is completely off

Disabling Fast Startup gives you a true cold start every time you boot. The hibernate file is not loaded, so the system initializes all hardware and drivers fresh. This can resolve slow boot issues caused by stale data in the hibernate file, especially after driver updates or hardware changes.

You can now control how Windows 11 handles the hibernate file and Fast Startup. To verify the change, restart your system and check the boot time. If you need to preserve battery life on a laptop, re-enable Hibernate mode with the full-type command while keeping Fast Startup disabled. For the fastest boot on a system with an SSD, consider using Sleep mode instead of Hibernate, as Sleep does not write a large file to disk.