The latest Windows 10 Insider build, number 18312, presents a new feature wherein the operating system reserves a big old chunk of disk room, effectively expanding its on-disk footprint by another 7GB.
The storage reservation is to confirm that certain critical operations—most significantly, installing advertise updates—always have enough free space available. Windows desires substantial extra disk space both during the installation of each part update (as it unpacks all the files) and afterward (as the previous version of Windows is hided untouched, so that you can roll back if necessary). Lack of free period is one of the more common reasons for updates failing to install, so Microsoft is background space available on a long-term basis, allowing those periodic updates to be positive they have what they need.
The exact amount rigid will depend on the optional features and language packs installed, but apropos 7GB will be typical. The reserved space isn’t entirely lost during common usage, with certain temporary files having their disk management charged against reserved space rather than free lapse. Being temporary, such files can be safely discarded each regulate an update is available to reinstate the full reserved capacity.
The reservation itself is executed within the NTFS file system. Each file system can deliver a reservation set, and free disk space will drop by the size of the territory. Files created for Windows updates are marked specially, allowing their accommodation usage to be charged against the reservation rather than regular unshackled space. It isn’t yet clear if the ability to create reservations will be a general-purpose effortlessness. Advanced file systems on some other platforms (such as ZFS in Solaris) list a general reservation facility that operates in a similar way to this update-specific process, so it’s not impossible to imagine Microsoft generalizing the capability.