Starting from Windows 8.1, Microsoft began using a new file format called ESD for installation packages.
With the extensive online testing of the Windows 10 Technical Edition by over 1 million users, the software company made the switch to require pre-existing software testers with an earlier version of the Windows 10 Technical Edition installed to update online via the Update and Recovery menu system using an Electronic Software Download (ESD) file instead of the typical public ISO image file which could be burned to a DVD.
Microsoft have been making changes to how they plan to deliver software.