Unknown File in Local Disk C - Windows 11

Yoga Samudra 20 Reputation points
2026-09-14T06:05:21.35+00:00

I was trying to free some memory in my Local Disk C until at first i stumbled upon this inconsistencies of memory between what i checked of all directories and files (even the hidden ones) in C and when i checked within the properties of the Local Disk C itself. Which you can see from picture 1 below.Anomaly in Disk C

You can see there is a gap of about 11 GB of data there. And then i tried scanning my Local Disk C using TreeSize and found out there is this one file with a size of 9 GB that i don't know the usage of it (Provided in picture 2). And can anyone explain to me what is this file and is this an important file? Thank you in advance!
Anomaly in Disk C part 2

Windows for home | Windows 11 | Files, folders, and storage
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Answer accepted by question author
DaveM121 932.3K Reputation points Independent Advisor
2026-09-14T06:42:42.73+00:00

File Explorer is not great at working out where data is used on your drive when showing all space used on the C drive, even with hidden files showing, it does not for example show the space used by the C:\Program Files\WindowsApps folder which contains all apps and games downloaded form the store or built-in Windows apps.

In your screenshot of TreeSize, the files in that section you have expanded, those are Windows system files used for virtual memory, Hibernation... etc. and those are all indicated as normal size, so is the Windows folder, there is no problems indicated.

The Users folder is the only folder that contains a lot of date, in TreeSize, expand out that Users folder and dog down to find where most of that 78.7GB of data is used, and please provide a screenshot of what you find in there.

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  1. AI answer

    2026-09-14T06:05:39.05+00:00

    The size difference is typically caused by hidden or system-protected files that normal File Explorer size checks do not report accurately. That matches what is shown in the screenshots.

    The 9 GB group in the root of C:\ appears to be mostly:

    • hiberfil.sys — about 4.8 GB
    • pagefile.sys — about 4.3 GB
    • swapfile.sys — a small amount

    These are system files.

    • hiberfil.sys is used by Windows power features.
    • pagefile.sys is used by virtual memory.
    • swapfile.sys is also a Windows system-managed file.

    These files are important for normal Windows operation or power-management features, so they should not be deleted manually.

    If the goal is to understand where the missing space is going, focus on hidden and system files, because Windows can show a gap between folder totals and drive usage when those files exist.

    To investigate large files on C:\, use a command that includes hidden and system files. For example:

    Get-ChildItem -Path "C:\" -Recurse -ErrorAction SilentlyContinue | Sort-Object Length -Descending | Select-Object FullName, Length -First 20

    Or from Command Prompt:

    dir C:\ /s /a /o-s

    If more space is needed, use Windows storage cleanup features instead of deleting unknown root files manually:

    1. Open Start > Settings > System > Storage.
    2. Turn on Storage Sense.
    3. Open Cleanup recommendations.
    4. Review suggested files and select Clean up.

    If the space usage keeps growing unexpectedly, the documented common cause is large temporary files created by applications in hidden or system-protected folders. In that case:

    1. Back up the system or affected folders first.
    2. Identify which application is creating the large temporary files.
    3. Remove only temporary files that are no longer needed.

    References:

    AI-generated content may be incorrect. Read our transparency notes for more information.

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