You might have more than one disk partition on your hard drive, and checking for disk partition on ubuntu is easy to do, you can do it from the command line, i'm going to show you right now.
There are some commands that you can use to check disk partition on ubuntu such as fdisk, cfdisk, parted, and lsblk, here's how to use them:
The 'cfdisk' is more advanced command, not only display the partition you can also do something else, like delete partition, set bootable partition and so on.
The 'parted' command only display info about disk partition on your computer.
Last but not least the 'lsblk' command, this one will only display minimum information about disk partition on your system, but this one you don't need to run with sudo.