Quote:Microsoft revealed today that it plans to integrate a feature called reserved storage in Windows 10 version 1903, the next feature update of the operating system.

Windows 10 will set aside some available storage automatically so that it is  used exclusively by the operating system.

Quote:Through reserved storage, some disk space will be set aside to be used by updates, apps, temporary files, and system caches.

Microsoft wants to improve the reliability of "critical OS functions" that rely on disk space, e.g. updating or caching, by reserving disk space.

Existing devices won't have the reserved storage functionality enabled by default; new Windows 10 version 1903 installations and systems that come pre-installed with that particular version of Windows 10 -- and future versions -- will make use of reserved storage automatically.

Full reading: https://www.ghacks.net/2019/01/08/windows-10-reserved-storage-explained/