Wubi (software)

Wubi ("Windows-based Ubuntu Installer") is a free software Ubuntu installer, that was the official Windows-based software, from 2008 until 2013, to install Ubuntu from within Windows, to a single file within an existing Windows partition.

After installation, it added a new "Ubuntu" option to the existing Windows boot menu which allowed the user to choose between running Linux or Windows, and avoided the need to re-partition the disk. Provided by Wikipedia