Starting with Windows 10 version 1903, there is a new feature called Reserved Storage. As the name suggests, Reserved Storage is nothing but a certain amount of disk space set aside by Windows 10 for Windows Updates, apps, temporary files, and system caches.
The idea behind Reserved Storage is to always have some disk space for Windows Update, temporary files, system caches, and apps. As you likely know, Windows operating system and other apps might not work as expected when the disk is full. By enabling the reserved storage, you can make sure that Windows 10 will always
The amount of storage reserved starts at about 7 GB and the same varies over time based on how you use your Windows 10 computer. As you can see in the picture below, on my PC, reserved storage is using just 2.5 GB of disk space.
Optional features and installed languages affect the reserved storage size. When it’s time to install an update, Windows 10 will automatically delete temporary files and other unwanted OS files in the Reserved Storage to give the full reserved storage for Windows Update. If an update requires more space available than in the reserved storage, it will automatically use the free space available outside the reserved storage. Once the update is installed, all temporary files and downloaded update files will be removed.
One can navigate to Settings app > System > Storage, click Show more categories link and then click on System & reserved to check the disk space set aside for the Reserved Storage feature.
If you would like to disable the Reserved Storage feature in Windows 10, you need to make a small change to Windows Registry. Currently, Windows 10 doesn’t offer an option in the Settings to turn on or off Reserved Storage.
Enable or disable Reserved Storage in Windows 10
Step 1: Open the Registry Editor by keying in Regedit in Start/taskbar search field and then hitting the Enter key.
Step 2: Navigate to the following registry key:
TIP: Simply copy and paste the above registry path in the Registry Editor’s address bar and then press the Enter key to quickly navigate to the key.
Step 3: On the right-side, look for ShippedWithReserves and double-click on it to open its properties.
Step 4: Set the value data to 0 to disable the Reserved Storage. Setting the value data to 1 will enable the Reserved Storage in Windows 10.
How to update Windows Update size in Windows 10 guide might also interest you.