(although I do not think that is relevant to this case.) The laptop used is a Lenovo L560 and the harddisk is an SSD with 750GB I have searched various forums for answer related to my question but since I already have installed the exact same settup two times I'd rather have the advice of someone experienced in these matters if possible :-) I have powered down Windows 10 turning of Fast Boot and Secure Boot is disabled via the BIOS settings. Please note that I have installed Windows 7 on a partition of 75GB and Windows 10 on a partition with 150GB, so I suppose the partition marked as 'unknown' should be the partition of Windows 10. Ubuntu installation screen when I select the 'Something Else' option: Ubuntu installation step where I stopped: Windows 10 dual boot (text is german - means: Select Operating System): I tried to install Ubuntu anyway before (same setup as described) but ended up loosing access to Windows 7. However: If I try to install Ubuntu 16.04 not both already installed Windows versions are recognized. I have a working dual boot system (Windows 7 Pro 64bit and Windows 10 Pro 64bit) and want to install Ubuntu 16.04 from a live USB stick in order to have a working triple boot system (please note that this settup is required and virtualization of Windows 7 is sadly not an option).

Windows 7 dual boot setup