Taken integrally from https://askubuntu.com/questions/219514/where-to-install-bootloader-when-installing-ubuntu-as-secondary-os
Here's an example that could help you out:
Under "Device for boot loader installation":
- if you choose dev/sda, it will use Grub (Ubuntu's boot loader) to load all systems on this hard drive.
- if you choose dev/sda1, Ubuntu need to be manually added to drive's boot loader after installation. (for example, you previously have Windows installed on another partition of this drive, you'll need manually add Ubuntu into mbr)
