Microsoft's latest Windows 10 19H1 Fast Ring test build is the first which allows users to see how Windows 10 will manage disk space, going forward. That coming storage-focused feature, known as Reserved Storage, will kick off in either today's Windows 10 build (No. 18312) or the next, depending on when testers complete a quest.
Those Windows Insider testers who run through this quest before installing today's build will see Reserved Storage kick off for this test build. Those who do the quest after installing Build 18312 should see that feature in the next Windows 10 19H1 test build, according to Microsoft's January 9 blog post about Build 18312.
Reserved Storage, as Microsoft officials detailed earlier this week, will retain about 7 GB of disk space (but possibly more) so that updates can be installed smoothly, even on storage-constrained PCs. Given that a number of Windows 10 users have encountered problems when attempting to install Microsoft's Windows 10 feature updates due to storage constraints, Reserved Storage is Microsoft's latest attempt at a solution. Officials said Reserved Storage will be introduced automatically on PCs that come with 19H1 preinstalled or on PCs where 19H1 was clean-installed.
There are some additional updates and tweaks in Build 18312, including some adjustments to the "Reset this PC" user interface. Microsoft also has added some new command-line options to the Windows Subsystem for Linux command-line tool in the name of improved WSL management.
There are quite a few known issues in today's test build, plus some other additional minor updates, which are listed in Microsoft's blog post about Build 18312.
Windows 10 19H1, which may be known as Windows 10 1903 once it's available, should begin rolling out to mainstream users around April 2019, if Microsoft sticks to its current feature-update timetable.