Hiberfil.sys is a hidden system file on your Windows computer, and it plays a critical role in how your PC handles power-saving states. While many users are aware of its existence due to the significant amount of disk space it consumes, few understand its true purpose and its intricate relationship with features like hibernation and Fast Startup.
This comprehensive guide will not only explain what hiberfil.sys is but also provide a deep dive into the Windows power states that use it. We’ll explore the pros and cons of keeping the file, and then I’ll give you a detailed, step-by-step tutorial on how to safely disable hibernation, delete the file, and reclaim valuable storage space on your hard drive, particularly on a smaller SSD where every gigabyte counts.
Understanding the Windows Power States
Before we can talk about hiberfil.sys, it’s important to grasp the different power states your computer uses. The way a PC saves its current state directly impacts whether this file is created and how large it becomes.
Sleep (S3): This is a low-power state. Your computer’s state (all your open applications and documents) is stored in the Random Access Memory (RAM). The RAM remains powered on, which allows for a near-instantaneous wake-up. However, because the RAM is still drawing power, this state is not ideal for long periods. The hiberfil.sys file is not used in this state.
Hibernate (S4): This is a true power-saving state. When your computer enters hibernation, it takes a snapshot of everything in your RAM and saves it to a file on your hard drive—that’s hiberfil.sys. The system then completely powers down, drawing no power at all. When you turn the computer back on, it loads the contents of the hiberfil.sys file back into RAM, restoring your previous session exactly as it was. While it’s slower to wake up from than sleep mode, it’s perfect for saving battery life on laptops when you won’t have access to an outlet for a while.
Hybrid Sleep: This state is a combination of Sleep and Hibernate. It’s most commonly used on desktop computers. It saves your session to both RAM (like sleep) and the hard drive (like hibernate). This gives you the speed of a quick wake-up from sleep, but if there’s a power failure, your session is still safely saved on the hard drive. Hybrid Sleep also uses the hiberfil.sys file.
Fast Startup (Hybrid Shutdown): This feature, which is enabled by default in Windows 10 and 11, is a form of hibernation designed to speed up your boot time after a full shutdown. When you “shut down” your computer with Fast Startup enabled, Windows closes all your applications and logs you off, but it saves the state of the Windows kernel and system drivers to the hiberfil.sys file. When you turn the computer back on, it loads that kernel state from the hard drive instead of performing a cold boot, which is why your PC starts up so much faster. This is the most common reason why many users who never intentionally use hibernation still have a very large hiberfil.sys file.
The hiberfil.sys File: A Deep Dive
The hiberfil.sys file is an essential part of the hibernation process, and its characteristics are what make it a point of interest for many PC users.
The file’s primary purpose, as we’ve discussed, is to act as a temporary storage container for your system’s RAM. Think of it as a virtual copy of your computer’s short-term memory that gets written to the hard drive. Because it needs to hold a complete mirror of your RAM, the size of hiberfil.sys is directly proportional to the amount of RAM you have installed. It’s typically around 75% of your total RAM. So, if your computer has 16 GB of RAM, the hiberfil.sys file can be as large as 12 GB. This is a significant amount of space, especially on smaller, faster SSDs that are common in modern laptops and desktops.
The file itself is a hidden system file. By default, Windows hides system files from view to prevent accidental deletion or modification. You can find it in the root directory of your system drive, which is almost always the C: drive. To see it, you would need to adjust your folder view settings to “Show hidden files and folders” and “Hide protected operating system files.”
The Pros and Cons of Hibernation
Disabling hibernation is a trade-off. While it can free up a lot of space, it means giving up a useful feature. It’s important to weigh the benefits against the drawbacks before you decide.
The Pros of Hibernation:
Power Savings: Hibernation uses almost no power, making it the most power-efficient option for long periods of inactivity, especially for laptops. If you’re going to be away from your computer for a few hours but want to keep your session, hibernation is a great way to save battery life.
Quick Session Resume: When you use hibernation, your desktop, all your open applications, and browser tabs are saved. When you resume, everything is exactly where you left it. This can be a huge time-saver compared to a full shutdown and restart where you have to manually reopen everything.
Session Preservation: If you’re working on something important and your laptop battery dies, hibernation can be a lifesaver. Because the session is saved to the hard drive, your work is preserved even if the power cuts out completely.
The Cons of Hibernation:
Large Disk Space Consumption: This is the main reason people want to disable it. On a computer with 16 GB of RAM, reclaiming 12 GB of space can be a huge win, especially if you have a small SSD.
Slower to Resume than Sleep: While it’s faster than a cold boot, waking up from hibernation is noticeably slower than waking up from sleep mode, as the system has to read a massive file from the hard drive back into RAM.
Potential for Driver Issues: In some rare cases, hibernating can cause issues with certain drivers, leading to crashes or unpredictable behavior. This is much less common on modern hardware, but it can still happen.
SSD Wear and Tear: This is a minor concern for most users, but it’s worth mentioning. Because hibernation involves writing a very large file to your SSD, it contributes to the wear on the drive. For a modern SSD, this is unlikely to be a problem, as they are rated for massive amounts of data writes, but it is a factor.
Disabling and Deleting hiberfil.sys
The most effective way to delete the hiberfil.sys file and prevent it from coming back is to disable the hibernation feature entirely. This process is straightforward but requires a specific command.
Step 1: Open an Elevated Command Prompt or PowerShell
You need to have administrator privileges to run the necessary command. Don’t just search for “Command Prompt” and click it. Instead, follow one of these methods:
Right-click the Start button, and from the context menu, select “Command Prompt (Admin)” or “Windows PowerShell (Admin)“.
Click the Start button, type “cmd” or “powershell,” right-click the result, and select “Run as administrator.”
A User Account Control (UAC) dialog will pop up asking for permission. Click “Yes.” You will know you are in an elevated prompt because the window title will begin with “Administrator.”
Step 2: Check Your Current Hibernation Settings (Optional but Recommended)
Before you make any changes, you can check the current state of your system’s hibernation capabilities. In the Command Prompt window, type the following command and press Enter:
powercfg /a
This command will list all available sleep states and tell you whether hibernation is currently enabled or disabled. It will also show you the Fast Startup status. This is a great way to confirm the changes later.
Step 3: Disable Hibernation
This single command will disable both hibernation and Fast Startup, and it will also delete the hiberfil.sys file for you.
Type the following command into the Command Prompt window and press Enter:
powercfg /h off
You won’t see any confirmation message, but if the command prompt returns to the next line without an error, it worked. This command tells Windows to turn off the hibernation feature. Windows then recognizes that the hiberfil.sys file is no longer needed and automatically deletes it from the root directory of your C: drive. You don’t need to manually delete the file.
Verifying and Reclaiming Disk Space
After running the command, it’s a good idea to verify that it worked and that your disk space has been freed up.
Step 1: Restart Your Computer
For the changes to fully take effect and for Windows to complete the process of deleting the file, you should restart your computer.
Step 2: Verify that Hibernation is Disabled
Open your elevated Command Prompt again and run the powercfg /a command. The output should now say that “Hibernate” is not available on your system. This confirms that the feature has been successfully disabled.
Step 3: Check Your Disk Space
Navigate to “This PC” or “My Computer” and check the disk space on your C: drive. You should see that a significant amount of space has been reclaimed. The amount will be roughly the size of your system’s RAM.
It’s important to remember that this process also disables Fast Startup. For most users with an SSD, this is a minor trade-off, as the drive’s inherent speed is usually enough to provide a fast boot time. If you have an older hard drive, you might notice that your boot time has increased, as Windows is now performing a full shutdown and cold boot every time.
Re-enabling Hibernation
If you decide later that you miss the hibernation feature or want to re-enable Fast Startup, you can do so easily.
To re-enable hibernation, simply open an elevated Command Prompt and run the following command:
powercfg /h on
This command will tell Windows to re-enable the feature and will create a new hiberfil.sys file on your system drive. You may need to restart your computer for the changes to fully take effect.
If you specifically want to re-enable Fast Startup but not hibernation, you must go through the Control Panel.
Open the Control Panel and navigate to “Hardware and Sound” > “Power Options.”
In the left-hand pane, click “Choose what the power buttons do.”
Click “Change settings that are currently unavailable.”
Scroll down, and under “Shutdown settings,” you can check or uncheck the “Turn on fast startup (recommended)” box.
Click “Save changes.”
Troubleshooting and Advanced Tips
While the process is usually smooth, you might run into a few issues or want to customize your experience.
Permission Denied: If you see an “Access is denied” error when you run the command, it means you did not open the Command Prompt as an administrator. Close the window and try again using one of the methods mentioned in Step 1.
Hibernation File Still Exists: If you ran the command and the file still appears to be on your system, it’s likely a caching or display issue. A restart will almost always resolve this. You can also try adjusting your folder view settings again to ensure the file is visible.
“My hiberfil.sys file is still huge!” By default, the hiberfil.sys file is roughly 75% of your total RAM. If you want to keep the hibernation feature but reduce the size of the file, you can do so. This is a great option for users who want to use Fast Startup but are short on disk space.
Open an elevated Command Prompt.
To set the file size to 50% of your RAM, run:powercfg /h /type reduced
To set the file size back to full size (75% of RAM), run:powercfg /h /type full
SSD vs. HDD: The decision to disable hibernation is often more critical for users with SSDs. The space reclaimed on a 256 GB or 512 GB SSD can make a huge difference in day-to-day usability. On a traditional HDD with terabytes of space, the trade-off is much smaller. While the write-wear on an SSD from hibernation is generally not a concern, reclaiming a large chunk of space is a compelling reason for many to disable it.
The hiberfil.sys file is an integral part of Windows’ power management system, enabling useful features like hibernation and Fast Startup. For users with limited storage, especially on an SSD, disabling these features is a quick and effective way to free up a substantial amount of disk space.
By running a simple command from an elevated Command Prompt, you can safely disable hibernation, automatically deleting the hiberfil.sys file in the process. Remember the trade-offs: you will lose the ability to hibernate and your computer’s boot time might increase if you’re on a traditional hard drive. But for many, the extra space is worth it.
