The rest of the space should be unallocated data. Right Click on "Computer" in the Start menu and select "Manage". Double Click on Storage, and then double click on "Disk Management".
You should see your 100GB partition here marked as "Healthy - System, Boot, Active, etc". Then another entry will be for the unallocated space, which will be whatever is left of the drive.
You can divide this unallocated space up into more partitions or make it all a single, second partition. I believe you can do this within Windows but I am not completely sure. If not, you'll need a third party disk partitioning program.
You should see your 100GB partition here marked as "Healthy - System, Boot, Active, etc". Then another entry will be for the unallocated space, which will be whatever is left of the drive.
You can divide this unallocated space up into more partitions or make it all a single, second partition. I believe you can do this within Windows but I am not completely sure. If not, you'll need a third party disk partitioning program.
