Windows 10 deploys a compression algorithm that enables the operating system to reclaim 1.5GB of storage on 32-bit systems, and up to 2.6GB in 64-bit Windows. This system is called Compact OS, and depending on a number of variables, such as processor speed, available RAM, and disk type and size, Windows automatically enables compression of system files during the upgrade process. If Compact OS is enabled, Windows Universal Apps are compressed to save space.
To determine if Compact OS is enabled on your system, open a command prompt and type compact /CompactOS:query.
If you want to manually enable or disable Compact OS, open a command prompt with administrator privileges, and run compact /CompactOS:always or compact /CompactOS:never.