When you are hunting for big files on your Windows PC, you may come upon several large system files. One of them may be hiberfil.sys, which Windows uses for its hibernation feature and some other features.
The file has a size that is roughly 40 percent of the system RAM. If you have a PC with 16 gigabytes of RAM, it should have a size of about 6,4 gigabytes. This climbs to more than 12 gigabytes on a 32 GB system.
The file hiberfil.sys is found in the root location of the c: drive on Windows PCs by default.
The main hiberfil.sys functions
1. Hibernation
Windows creates a snapshot of the RAM, including open apps, documents and browser tabs, and writes the data directly to the hibernation file hiberfil.sys.
Once it is saved, Windows shuts down completely and doesn’t need electricity anymore. When the PC is turned on again, Windows reads the file and loads the snapshot back in memory, so that the previous session is restored.
2. Fast Startup (Fast Boot)
Introduced in Windows 8 and active by default in Windows 10 and 11, Fast Startup speeds up the time it takes for a PC to turn on.
When shut down is selected, Windows logs out the user and closes any app that is open. It saves the core Windows system and loaded drivers into the hiberfil.sys file.
The next time Windows is powered on, the operating system loads the file from the drive into RAM, which improves the time it takes to start the system, especially on devices with older or slow hard drives.
3. Hybrid Sleep
This feature is primarily used on desktop computers. When a desktop goes to “Sleep,” it enters a low-power state that keeps the RAM active for instant wake-ups. However, as a safety measure, Windows simultaneously writes a copy of the RAM to hiberfil.sys.
If the PC loses power, Windows can restore the state so that uncompleted work is not lost.
Why you may consider shrinking the file
While hiberfil.sys provides useful power and startup functions, there are several practical reasons users—especially desktop power users and gamers—choose to shrink it or delete it entirely.
1. Reclaiming Significant Storage Space
This is the main reason for most users. You can reclaim gigabytes of storage space by shrinking or eliminating the hiberfil.sys on your system. While that is not a problem on systems with plenty of disk space, every gigabyte counts on systems with 128 GB or, god beware, 64 GB of hard drive space.
- High-RAM Systems: On a PC with 32 GB, 64 GB, or 128 GB of RAM, hiberfil.sys can use two-digit gigabytes of space on the main OS drive (C:), even if Hibernation is never used.
- Small SSDs: For users running Windows on smaller boot drives (such as 128 GB or 256 GB SSDs), reclaiming that space can make a massive difference in keeping the system running smoothly.
2. Reducing Unnecessary Write Wear on SSDs
Solid-State Drives (SSDs) have a finite lifespan determined by Terabytes Written (TBW). Every time a system hibernates or undergoes Fast Startup shutdowns, Windows dumps gigabytes of data onto the drive.
- Disabling or reducing
hiberfil.syseliminates continuous large-file write cycles. - While modern NVMe drives are quite durable, minimizing redundant writes helps maximize drive longevity.
3. Fast SSDs Render “Fast Startup” Obsolete
Windows Fast Startup was designed during the era of slow, mechanical HDDs to speed up boot times.
- On modern NVMe SSDs, a cold boot from a completely turned-off state takes just a few seconds.
- Because the speed improvement from Fast Startup is practically imperceptible on modern drives, many users prefer to turn it off completely and get their disk space back.
4. Fixing System Bugs & Driver Issues
Fast Startup doesn’t actually shut down Windows—it saves a kernel session state. Over time, this can lead to system instability:
- Stale Drivers & Memory Leaks: Unstable device drivers or memory leaks can persist across reboots because the system kernel never truly gets refreshed.
- Troubleshooting: System administrators often disable hibernation to force Windows to execute clean full reboots every time.
How to shrink or disable hiberfil.sys on Windows 11
- Press the Windows-key.
- Type cmd.
- Select “run as administrator” to open an elevated terminal window.
- Click “yes” when asked for permission.
To completely disable hiberfil.sys on the system, type:
- powercfg -h off
To shrink hiberfil.sys instead, type:
- powercfg /h /type reduced
To undo the change at any time, type:
- powercfg /h /type full
Shrinking vs. disabling: the differences
When deciding how to manage hiberfil.sys, the choice ultimately comes down to one question: Do you still want to use Windows’ “Fast Startup” feature?
Here is exactly how the two options compare:
| Feature / Impact | Shrinking (type reduced) | Disabling (off) |
| File Status | Kept, but shrinks to ~20% of your total RAM | Completely deleted (0 bytes) |
| Fast Startup | Remains active | Disabled (PC performs a true “cold boot”) |
| Hibernation (App state) | Disabled | Disabled |
| Hybrid Sleep | Disabled | Disabled |
| Space Reclaimed | Moderate (frees ~50-80% of the file’s original size) | Maximum (frees 100% of the file’s footprint) |
Which should you choose?
Choose “Shrinking” if:
- You have a slower drive: If you are running Windows on a mechanical hard drive (HDD) or an older SATA SSD, Fast Startup noticeably improves your boot times.
- You want a compromise: You want to reclaim a few gigabytes of space but don’t want to sacrifice the quick boot speeds you are used to.
Choose “Disabling” if:
- You have a modern NVMe SSD: On fast modern drives, a traditional “cold boot” only takes a few seconds longer than Fast Startup. The massive storage savings are usually worth the 3-second longer boot time.
- You want a “Clean Slate” shutdown: Because Fast Startup saves the system kernel to the drive, bugs, memory leaks, and driver issues can persist across reboots. Disabling the file forces Windows to load fresh every time you turn on the PC.
- You Dual-Boot: If you run Linux alongside Windows, Fast Startup leaves the Windows drive in a locked state. Disabling the file ensures you can safely access your Windows files from your Linux partition.
1. Check size–I used Everything; hiberfil.sys was 11.55GB.
2. Check for clutter: Go to System, Storage, and click the “show more categories.” Review as necessary. Even though I don’t download to the Download folder, I had GBs of useless stuff in the folder. Delete as necessary. That alone saved me three times the size of the hiberfil.sys file. Documents had a lot of old junk as well.
3. Run Disk Cleanup; mine was fine with only 1.2 GB of non-essentials.
I use Hibernate on my main laptop, so, for me, deleting the hibefil.sys isn’t an option. And I’ve used Hibernate for months, years–it may be a myth, but it’s not growing exponentially.
Some users may prefer TreeSize instead of MS built in tools.
“You can reclaim gigabytes of storage space by shrinking or eliminating the hiberfil.sys on your system.” Not exactly true for everyone as documented above.
On a 500GB SSD, 11,5GB isn’t that much.
Clean up old Restore Points–eliminated about 15 of those–each is about 1GB.
I could do a cleaning of numerous other files and reg keys, but it’s not necessary at this point. Laptop is running fine.
I once believed that hiberfil.sys information, but I discovered years ago: It depends on the system and the clutter elsewhere.
My experience–keep Fast Boot on. Period. And Prefetch, Superfetch. SSDs have loads of spare writes and rewrites.
Martin,
In your article there’s only one passing mention of Windows 10, but several direct ones of Windows 11. You might like to make it a little clearer in the article, and especially in the heading, that hiberfil.sys also exists on Windows 10 (it comes in at 6,5GB on my Win10 Pro 23H2 + ESU), and that powercfg is a supported command.
The same remarks apply to your recent article on the secret installation of Onedrive Photos. Since July 27th I have that too.
Michael, you are right. Thanks for mentioning this!