We Couldn’t Update the System Reserved Partition: How to Fix It

Applies to: Windows 11 and Windows 10 feature updates and upgrades that fail with “Windows couldn’t be installed. We couldn’t update the system reserved partition”, often together with error codes such as 0xc1900201 or 0x800f0922.

What the error means

Every Windows PC has a small hidden partition that holds the boot files. On PCs that start in UEFI mode with a GPT disk (nearly all PCs sold in the last decade) it’s the EFI System Partition, often only 100 MB. On older PCs that start in legacy BIOS mode with an MBR disk it’s the System Reserved partition.

A feature update has to write new boot files to that partition. If it’s nearly full, setup stops with this message. The space is usually taken by:

• Boot font files that Windows itself puts there.
• BIOS recovery images and tools that some PC makers store on the EFI partition.
• Leftover boot files from another operating system, such as an old Linux install.

Your files and apps aren’t at risk: Windows simply rolls back and keeps running the version you had. The fix is to free some space on that partition.

Before you start: you’ll be working on the partition your PC boots from. Delete only the files named below, and back up anything important first. If you’re not comfortable with command-line steps, the update can wait until someone can help.

Step 1: Check your partition style and size

1. Press Win + X and select Disk Management.
2. Right-click Disk 0 (the disk with your C: drive) on the left, select Properties, open the Volumes tab and look at Partition style: GPT or MBR.
3. In the main view, find the small partition labelled EFI System Partition (GPT) or System Reserved (MBR) and note its size.

With GPT, follow Step 2. With MBR, skip to the legacy BIOS/MBR section.

Step 2 (UEFI/GPT): Free space on the EFI partition

Open Command Prompt as administrator: press Win, type cmd, right-click Command Prompt and select Run as administrator. Use Command Prompt, not PowerShell, because del works differently there. Run the commands one at a time:

mountvol Y: /s
dir Y:\
del /q Y:\EFI\Microsoft\Boot\Fonts\*.ttf
dir Y:\

• mountvol Y: /s gives the EFI partition the drive letter Y:. If Y: is already used, pick another unused letter and change it in every command.
• The first dir Y:\ shows the free space at the bottom (“bytes free”).
• The del command removes the boot font files. Windows Boot Manager then falls back to its basic built-in font, which mainly affects how some non-Latin languages look on boot screens. A later update can restore the fonts.
• The second dir shows how much space you gained.

Aim for at least about 20 MB free. If you have that, go to Step 4.

Step 3: Find what else is filling the partition

If deleting the fonts wasn’t enough, list the ten largest files on the partition (still in the administrator Command Prompt):

powershell -command "Get-ChildItem Y:\ -File -Recurse | Sort-Object Length -Descending | Select-Object FullName, Length -First 10"

Look for folders that don’t belong to Microsoft, such as a folder named after your PC maker containing BIOS recovery files, or a folder left behind by Linux. Then:

• Never delete anything under Y:\EFI\Microsoft\Boot except the fonts, or Y:\EFI\Boot. Those are the files your PC needs to start.
• PC maker files: BIOS recovery images can be needed to recover from a failed BIOS update. Rather than deleting them, copy them to another drive first (for example copy Y:\EFI\Maker\Bios\Recovery\*.* C:\EFI-backup\, using the real folder name) and check your PC maker’s support site for guidance before removing them.
• Old Linux boot files: if you no longer have Linux installed, a folder such as Y:\EFI\ubuntu is no longer needed. Copy it somewhere safe before removing it.

Legacy BIOS/MBR PCs: Clean the System Reserved partition

On MBR disks the fonts live on the System Reserved partition, which mountvol /s doesn’t mount. Give it a temporary drive letter instead:

1. In Disk Management, right-click System Reserved, select Change Drive Letter and Paths, then Add and assign Y.
2. In an administrator Command Prompt, take ownership of the fonts folder and grant yourself access:

takeown /d y /r /f Y:\Boot\Fonts
icacls Y:\Boot\Fonts /grant administrators:F /t
del /q Y:\Boot\Fonts\*.ttf

Then check the free space in Disk Management. When you’re done, remove the drive letter again (Change Drive Letter and Paths, select Y:, Remove) so the partition stays hidden.

If the System Reserved partition is very small (100 MB or less), consider converting the disk to GPT and switching to UEFI as part of the Windows 11 upgrade. That’s a bigger change with its own requirements, so plan it with a full backup.

Step 4: Unmount and retry the update

On GPT PCs, remove the temporary drive letter (a restart also removes it):

mountvol Y: /d

Restart, then go to Settings > Windows Update and select Check for updates, or run the Installation Assistant or ISO setup again. If the update now fails with a different code, see error 0x8007001f for the general update checks, or Windows Update from the command line for resetting the update components.

Permanent fix: Make the EFI partition bigger

Clearing the fonts usually works, but a 100 MB EFI partition can fill up again with the next feature update. Microsoft’s current partition guidance calls for an EFI System Partition of at least 200 MB, or 300 MB on drives with 4K native sectors.

Windows’ own Disk Management can’t grow the EFI partition, because it sits before the C: partition. Doing it means shrinking C: and moving partitions with a third-party partition tool, or a clean install that recreates the partitions. Either way:

• Make a full system image or file backup first, and have a Windows USB installer ready.
• If BitLocker or device encryption is on, save the recovery key from your Microsoft account or suspend protection before changing partitions.
• Don’t interrupt the tool while it moves partitions; plug a laptop into power.

If the PC stops starting after partition work, the boot files may need repairing. Our guide to the “Windows RE image was not found” error covers the recovery partition, and black screen fixes covers startup problems.

Related guides

• Error 0x8007001f in Windows Update: 8 ways to fix it
• Windows Update from the command line
• “Windows RE image was not found”: how to fix it
• Windows Resource Protection could not perform the requested operation (SFC and DISM)

Official sources: for more detail, see Microsoft’s own documentation:

• Microsoft Learn: UEFI/GPT-based hard drive partitions (EFI partition sizes)
• Microsoft Learn: mountvol command reference
• Microsoft Q&A: How to fix “We couldn’t update the system reserved partition”

Frequently asked questions

Is it safe to delete the files in EFI\Microsoft\Boot\Fonts?

Yes, those are only display fonts for boot screens. Windows still starts without them. Don’t delete anything else in the Boot folder.

How much free space does the update need?

Microsoft doesn’t publish an exact number. In practice, around 15 to 20 MB free on the EFI partition is usually enough; more is better.

Can I skip this by using the Windows 11 ISO?

No. Every upgrade method writes new boot files to the same partition, so it needs the free space too.

The error came back after the next update. Why?

Updates can put fonts and other files back. Repeat Step 2, and consider the permanent fix of enlarging the EFI partition.