You're poking around your C: drive, trying to figure out why your 512GB SSD is suddenly gasping for air, and you see it. A massive, monolithic file sitting right in the root directory named hiberfil.sys. It’s huge. We're talking 6GB, 12GB, maybe even 30GB depending on your setup.
What is it? Can you kill it? Or will deleting it turn your laptop into a very expensive paperweight?
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Basically, hiberfil.sys is the "memory dump" Windows uses for hibernation. When you tell your computer to hibernate—not sleep, but hibernate—Windows takes everything currently sitting in your RAM and writes it onto your hard drive. It stuffs all your open Chrome tabs, that half-finished Word doc, and your background apps into this one file so it can power down completely.
When you flip the lid back up, Windows sucks that data back into RAM. It feels like magic because everything is exactly where you left it.
The weird relationship between hiberfil.sys and Fast Startup
Most people think, "I never use Hibernate, so why do I have this 15GB file?"
Here's the kicker: even if you never click the "Hibernate" button, Windows 10 and Windows 11 use this file for something called Fast Startup.
Since the days of Windows 8, Microsoft decided that a "cold boot" (starting from zero) was too slow. Now, when you click "Shut Down," Windows doesn't actually shut down everything. It closes your user apps, but it hibernates the OS kernel and drivers into—you guessed it—hiberfil.sys.
This is why your "Up time" in Task Manager might show 14 days even if you turned your PC off last night. You're not actually restarting; you're just waking up a very sleepy kernel.
Why is the file so massive?
The size of hiberfil.sys isn't random. It’s mathematically tied to your physical RAM.
By default, Windows sets the hibernation file to roughly 40% to 75% of your total RAM capacity. If you have 32GB of RAM, your hiberfil.sys might be eating 12GB or more. It needs enough "reserved" space to ensure that if you ever do hibernate, there's a bucket big enough to catch all those digital bits.
Honestly, for people with 64GB or 128GB of RAM, this becomes a genuine storage crisis. You’re losing a massive chunk of your SSD to a feature you might not even use.
Can you safely delete hiberfil.sys?
The short answer: Yes. But you can't just right-click and hit delete.
If you try to delete it manually in File Explorer, Windows will give you a "File in use" error or just rebuild it the moment you reboot. It's a protected system file. To get rid of it, you have to tell Windows to stop using the hibernation feature altogether.
Once you disable hibernation, the file vanishes instantly. No "Recycle Bin" involved. It just ceases to exist.
The trade-off: What you lose
Before you go nuking it, understand the stakes.
- No more Hibernation: Obviously. If your laptop battery dies, you won't have that safety net where the state is saved to the disk.
- Slower Boot Times: You are disabling Fast Startup. On a modern NVMe SSD, you might notice a 2-second difference. On an old mechanical hard drive? It’ll feel like an eternity.
- The "Restart" fix: Ironically, disabling this often fixes weird Windows bugs. Since Fast Startup keeps drivers in a "hibernated" state, bugs can persist across shutdowns. A true cold boot clears the slate.
How to manage or remove the hiberfil.sys file
If you've decided you want your space back, you have two real options. You can either kill it entirely or just put it on a diet.
Option 1: The Nuclear Phoenix (Full Disable)
This is for the people who want every gigabyte back.
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- Right-click your Start button and select Terminal (Admin) or Command Prompt (Admin).
- Type exactly this:
powercfg -h off - Hit Enter.
That’s it. No confirmation message, no fanfare. If you check your C: drive now (you'll need to enable "Hidden Items"), the file will be gone.
Option 2: The "Reduced" Compromise
Maybe you like Fast Startup, but you hate the 20GB footprint. You can set the file to "reduced" mode. This keeps the file just large enough for the OS kernel (Fast Startup) but removes the ability to hibernate your user apps.
In that same Admin Command Prompt, run:powercfg /h /type reduced
This usually shrinks the file size by about half. It's a great middle-ground for laptop users who want a quick boot but don't need to save 50 Chrome tabs to disk every night.
hiberfil.sys vs. pagefile.sys: Don't mix them up
People often confuse these two, but they serve totally different masters.
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While hiberfil.sys is for saving your state for later, pagefile.sys is "Virtual Memory." It’s an overflow tank. When your RAM gets full because you're editing 4K video or have too many tabs open, Windows moves the less-active data to the page file.
Pro tip: Do not disable the page file. Even if you have 64GB of RAM, some old programs and core Windows functions will literally crash if they don't see a page file present. Hibernation is optional; the page file is essentially mandatory for system stability.
Actionable Steps for your PC
If you are currently looking at a "Low Disk Space" warning, here is exactly what you should do:
- Check your RAM: If you have 16GB or more and an SSD, you probably don't need the full hiberfil.sys.
- Run the Reduced command: Use
powercfg /h /type reducedfirst. See if that frees up enough space. It’s the safest "non-destructive" move. - Audit your "Up time": Open Task Manager (Ctrl+Shift+Esc), go to the Performance tab, and look at Up time. If it says 30 days and you "shut down" every night, your Fast Startup is working overtime.
- Verify removal: If you go the
powercfg -h offroute, make sure to restart your computer immediately to ensure the system state is fully cleared and the file is properly unlinked from the boot process.
Reclaiming 10GB+ of space in thirty seconds is one of the easiest "wins" in Windows maintenance. Just remember that if you're on a laptop and you find yourself frequently running out of battery, hibernation is your best friend—don't kill it unless you're disciplined about saving your work.