https://www.windowscentral.com/windows-core-os
One of the big things Microsoft has been working towards with Windows Core OS is an improved Windows Update system that installs updates in the background and requires less than a minute to restart once those updates are ready to do so.
How it works is very similar to how Android and Chrome OS do updates today. On those platforms, the OS runs in two separate mirrored partitions, and when an update is ready to install, the update is downloaded and installed to the offline partition that you're currently not using. When that's done, the OS will ask you to restart, and while it may look like you're just rebooting, what's actually happening is you're booting into the partition that just spent 25 minutes installing an update in the background.
Windows Core OS keeps system updates to under a minute.
It boots right up, as if there was never an update waiting to be installed, and that's because all the installing has already been done while you were busy using the other online partition. Now, you've booted into the partition where the update is installed, and the partition you were just in becomes the offline partition for newer updates to be installed to down the line.
This should solve one of the big issues Windows has when it comes to updates. Updates can usually take anywhere between 5 to 30 minutes to install, and even longer on older devices. Windows Core OS solves this problem by making it so the user isn't unable to use their PC for no longer than a minute. It simply restarts like normal, and you're back up and running again.