When you come across a folder named $Windows.~BT or simply ESD at the root of the C: drive, the first reaction is often to want to delete it to free up space. However, this ESD folder in Windows 10 stores upgrade and system repair files that the system uses in the background, sometimes without any visible notification.
ESD File and Compression: Why Windows 10 Doesn’t Keep a Simple WIM
The ESD (Electronic Software Download) format is a highly compressed variant of the WIM format historically used by Microsoft for installation images. The install.esd file can be found in the sources folder of recent installation media, replacing the old install.wim.
The main difference lies in the compression rate. An ESD file weighs significantly less than a WIM containing the same system image. For downloading via Windows Update, this reduces bandwidth and transfer time.
In return, ESD images are considered read-only for maintenance tools like DISM. If you want to modify an image (add a driver, remove a component), you must first export the ESD index to a WIM, make the modifications, and then possibly recompress it back to ESD.
This two-step workflow is documented in the Windows ISO customization guides published in 2026. To understand in detail the esd folder windows 10 on Journal du Webmaster, this distinction between read-only and editable is the starting point.
ESD Folder at the Root of C: What Windows Really Places There
The folder C:ESD does not appear on all machines. It is typically created during a major upgrade of Windows 10 (upgrading from one version to another) or after downloading a Feature Update via Windows Update.
Inside, you typically find temporary files related to the upgrade, sometimes a subfolder “Windows” or “Download.” Once the update has been successfully applied, this folder may remain in place but empty, or contain remnants that are no longer useful.
Can the ESD Folder Be Deleted Safely?
If the upgrade is complete and the system is functioning normally, the contents of C:ESD are no longer directly useful. You can delete it manually or use the built-in Disk Cleanup tool in Windows, which offers to remove temporary installation files.
One precaution is still useful: check that the folder is indeed empty or only contains outdated download files. If an install.esd file is still present and an upgrade is in progress or planned, its deletion may cause the process to fail. The error code 50030 during the deployment of Feature Packs is related, in some cases, to the absence or corruption of the install.esd file in the source ISO, as documented by ManageEngine in its support sheets.
DISM Command and ESD File: System Repair in Windows 10
The other context in which the ESD format is encountered concerns the repair of the Windows component store. The classic command used for troubleshooting is:
DISM /Online /Cleanup-Image /RestoreHealth
By default, this command looks for its source files on Windows Update. When the connection is limited or Windows Update is problematic, you can point DISM to a local ESD file as a repair source.
- Mount or extract the installation ISO of Windows 10 corresponding to the installed version
- Locate the install.esd (or install.wim) file in the
sourcesfolder - Identify the index corresponding to the installed edition (Home, Pro) with
DISM /Get-WimInfo - Run the command with the parameter
/Source:pathinstall.esd
The index and version must match exactly the installed edition. A mismatch between the source image and the installed system causes a silent failure of the repair, without an explicit error message in some cases. Feedback on this point varies depending on the builds.
Converting ESD to WIM or ISO
Converting an ESD file to WIM is done via DISM with the /Export-Image command. You can then rebuild a bootable ISO from the resulting WIM. Community scripts hosted on GitHub automate this process for those managing machine fleets.
This conversion is particularly useful when recovering an ESD file downloaded by Windows Update (stored in C:$Windows.~BTSources) and wanting to make it a standalone installation media.
Disk Space and ESD Files: What Deserves to Be Cleaned
The folder $Windows.~BT, which often contains upgrade ESD files, can take up several gigabytes. After a successful update, Windows keeps these files for a period (to allow for a potential rollback), then marks them as deletable.
To reclaim this space properly:
- Open Disk Cleanup, click on “Clean up system files”
- Check “Temporary Windows installation files” and “Previous Windows installation(s)”
- Confirm the deletion
Manually deleting these folders via Explorer also works, but some files may be locked by the system. The built-in tool handles these locks automatically.
The empty ESD folder at the root of C: can be deleted without consequence once the upgrade is complete. It will only be recreated during the next major upgrade.
The ESD format remains a discreet but central cog in the Windows 10 update mechanism. As long as you do not touch the files during an ongoing upgrade, the risk of breakage is almost nil. The only vigilance to maintain concerns the exact match between the installed version and the source image when using DISM for local repair.
