Future version of Windows 10 will reserve system space for updates
MANILA, Philippines – Microsoft announced earlier this week that a future version of the Windows 10 operating system will set aside some space on your system drive to ensure "critical OS functions always have access to disk space."
The blog post from January 7 explained, "With reserved storage, updates, apps, temporary files, and caches are less likely to take away from valuable free space and should continue to operate as expected."
Microsoft added initial allotment for reserved space would be around 7 gigabytes (GB), though the amount of reserved space will change depending on how you use your computer or adjustments made in future updates.
Windows Insiders can test the reserved storage system if they're running build 18298. – Rappler.com