If you find that your hard drive space is low and you can’t figure out why, it might be the $Windows.~BT folder. This folder contains files related to upgrading your system to the latest version of Windows 10. They also take up a large amount of space; several gigabytes.
How do I delete the folders $Windows.~BT and $Windows.~WS
The $Windows.~BT folder is a hidden folder on the main drive where the Windows operating system is installed.
When you upgrade your older Windows system to Windows 10, or upgrade Windows 10 to a new build, all folders and files related to your previous Windows installation are stored in the $Windows.~BT folder. This folder also contains important log files that can help troubleshoot why the upgrade may not have been successful.
If you are running out of space on your hard drive, that is a good reason to delete the folder and all its contents.
