boot.sdi

System Deployment Image

An .sdi file is a System Deployment Image on Windows. The known file is boot.sdi, which carries a ram disk image for the boot process. Windows PE and the recovery environment start from such a ram disk. The boot configuration data points to the .sdi file. Deployment servers send it to clients during network boot.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.