If you run Ubuntu alongside Windows, I think they do all the partitioning for you. However, I had a devilish time installing Ubuntu to run alongside Windows 8 in UEFI mode.
I had to go through BIOS and install in Legacy ROM mode with boot to CD first in the lineup.
- When I wanted Windows, I would switch to UEFI.
- When I wanted Ubuntu, I would switch to Legacy ROM mode.
With that said, I shrunk my Windows OS partition to its bare minimum in Windows first -- all of your extra GB will automatically go into a different partition.
Next I installed Ubuntu in Legacy ROM mode -- it will not give you the option to run alongside Windows. It will give you two options: one to install Ubuntu and erase everything (don't do that) and another to just install and create your own partitions, (do that one). It will ask you to partition and it will show you your new partition with all your unused GB.
You will have to create 4 partitions, here are the steps:
- Click on the unused GB partition give it about 6GB mark it Linux swap.
- Click on the same unused partition and click on " / " give it about 100GB (or whatever you want).
- Click on the same unused partition click on " /home " give it about 100GB (or whatever you want).
- When you continue, it will tell you that you need one more partition with 1MB, then continue with the installation.
If you don't mind switching at startup in BIOS between UEFI (Windows) and Legacy ROM mode (Ubuntu), this may be a tolerable solution. When I got used to Ubuntu, I saved the Windows 8 program on a disk and completely got rid of it, reinstalled Ubuntu and all of the partition problems became resolved.
Keep in mind that if you figure out how to do it in UEFI, it still holds. Create your partitions when installing Ubuntu, choose "install and create your own partitions".