How to fix Windows 11 slow performance caused by a full system drive

Summary

This guide helps you troubleshoot and resolve: How to fix Windows 11 slow performance caused by a full system drive. Follow the steps below to fix the issue.

Common Causes

Windows 11 relies on free disk space for virtual memory, temporary files, and system updates. When the system drive (usually C:) drops below roughly 10–15% free capacity, performance can degrade noticeably — applications take longer to open, file operations stall, and the whole machine may feel sluggish. This guide walks you through identifying what is consuming space on your drive and safely removing unnecessary data to restore normal speed.

Quick Fix Steps

1. Open Settings > System > Storage and review what is using the most space.
2. Run Storage Sense to automatically clear temporary files and Recycle Bin contents.
3. Uninstall applications you no longer use.
4. Move large personal files (videos, photos, archives) to an external drive or cloud storage.
5. Delete old system restore points and shadow copies if they are consuming excessive space.

Detailed Instructions

Step 1: Check current disk usage

1. Press Windows key + E to open File Explorer.
2. Click This PC in the left sidebar.
3. Look at the C: drive. If the bar under the drive is red or nearly full, you are low on space.
4. Right-click the C: drive and select Properties to see used and free space in gigabytes.

Step 2: Run Storage Sense

1. Open Settings by pressing Windows key + I.
2. Go to System > Storage.
3. Toggle Storage Sense to On.
4. Click Storage Sense to configure it.
5. Under Cleanup of temporary files, tick Keep Windows running smoothly by automatically cleaning up temporary system and app files.
6. Under Configure cleanup schedules, set Run Storage Sense to Every week.
7. Set Delete files in my Recycle Bin if they have been there for over to 14 days.
8. Set Delete files in my Downloads folder if they haven’t been opened for more than to Never unless you are comfortable with automatic deletion.
9. Click Run Storage Sense now at the bottom of the page.

Step 3: Use the built-in Disk Cleanup tool

1. Press Windows key + S and type Disk Cleanup.
2. Select Disk Cleanup from the search results.
3. Choose the C: drive and click OK.
4. Wait while Windows calculates how much space you can reclaim.
5. Tick the following items:
   • Temporary Internet Files
   • Delivery Optimisation Files
   • Recycle Bin
   • Thumbnails
   • Windows Update Cleanup
   • Previous Windows installation(s) (if present and you are happy with the current Windows version)
6. Click OK, then click Delete Files to confirm.

Step 4: Uninstall unused applications

1. Open Settings > Apps > Installed apps.
2. Click the Sort by drop-down and select Size to see the largest applications first.
3. Review the list and identify programs you no longer use.
4. Click the three-dot menu next to an application and select Uninstall.
5. Follow the on-screen prompts to remove the application.
6. Repeat for any other unwanted programs.

Step 5: Find and move large files

1. Open File Explorer and navigate to C:\Users\YourUsername.
2. Use the search box in the top-right corner and type size:gigantic to find files larger than 128 MB.
3. Alternatively, type size:huge for files between 16 MB and 128 MB.
4. Review the results. Common culprits include video recordings, disk images, virtual machine files, and large archives.
5. Move files you want to keep to an external USB drive, network location, or cloud storage such as OneDrive.
6. Delete files you no longer need by right-clicking and selecting Delete.

Step 6: Reduce System Restore and shadow copy usage

1. Press Windows key + S and type Create a restore point.
2. Select Create a restore point from the results.
3. In the System Protection tab, select the C: drive and click Configure.
4. Drag the Max Usage slider to a lower value, such as 5% or 10% of the drive.
5. Click Delete to remove all existing restore points and shadow copies for that drive.
6. Click Apply, then OK.

Step 7: Clear browser caches and download folders

1. Open your web browser (Microsoft Edge, Google Chrome, or Mozilla Firefox).
2. Press Ctrl + Shift + Delete to open the clear browsing data dialogue.
3. Select Cached images and files and any other data you wish to remove.
4. Set the time range to All time.
5. Click Clear now or Clear data.
6. Open File Explorer and navigate to C:\Users\YourUsername\Downloads.
7. Sort by Size and review old installers, ZIP files, and other downloads you no longer need.
8. Delete unwanted files or move them to external storage.

Troubleshooting

Disk still full after following the steps above

If your drive remains critically low on space, consider the following:

• Check for hidden large folders using a tool such as WinDirStat or WizTree, which provide a visual breakdown of disk usage.
• Look for large pagefile.sys or hiberfil.sys files. You can disable hibernation by running powercfg /h off in an elevated Command Prompt, which removes hiberfil.sys.
• Check for Windows.old folders left over from a feature update. These can be removed using Disk Cleanup as described in Step 3.
• Review cloud storage sync folders such as OneDrive or Dropbox. Files marked as “online-only” do not use local space, but files set to “always available on this device” do.

Performance is still slow after freeing space

If you have freed up significant space but Windows 11 remains sluggish, the issue may not be disk-related. See our guide on Computer running slow for additional causes such as startup programs, malware, or insufficient RAM.

Applications continue to freeze or crash

If specific applications are unresponsive even after freeing disk space, refer to Applications freezing or crashing for further troubleshooting steps.

Browser performance issues persist

If web browsing remains slow after clearing caches, see Browser not loading pages for network and browser-specific guidance.

System instability or blue screens

If you experience blue screen errors during or after cleanup, review Blue screen of death (BSOD) – restart steps for recovery options.

Still Having Issues?