Ubuntu can install along side of windows, so you can boot both windows and Ubuntu on the same machine.

By default, the grub boot loader (used by ubuntu) is loading Ubuntu by default, but you can easily change that.

You need to look at the boot menu to get the name of the OS entry in the grub boot loader:

1. You’ll need to look at the boot menu to get the full name of the OS entry in grub loader configuration.
   Open a terminal, type command:
   grep menuentry /boot/grub/grub.cfg
2. You’ll see a bunch of entries for grub boot loader menu, copy or note down the entry for windows, make sure you include the whole name, including the parenthesis with location path. For example: Windows Vista (loader) (on /dev/sdc1)
3. Edit the /etc/default/grub file. Use command:
   sudo nano -B /etc/default/grub
4. Change the line GRUB_DEFAULT. For example:
   GRUB_DEFAULT=”Windows Vista(loader)(on /dev/sdc1)
5. Save the file in nano.
6. In the terminal, update the grub by using command:
   sudo update-grub