I am running Ubuntu 16.06 client virtually under Windows 7 Virtual Box. As normal to all user running another operating system virtually, I need to access the data on my Windows 7 from my Ubuntu.
[the version of Virtual Box that I am running now is 5.1.6, Ubuntu 16.04, and updated (Oct 2016) Windows 7 Pro SP1]
Under Virtual Box setting, you can easily share the folder on Windows 7 that you wish to access from Ubuntu. Simply go to Devices > Shared Folders > Shared Folders Settings...
From there you can choose the folder on Windows 7 that you wanted to shared to Ubuntu.
