I want to use a hard drive but it is 1TB and I also use it for file backups. Can I continue to keep my backups on it as well as using it for a portable OS? In other words, can I create the partitions without formatting the whole disk?
You can perform hard disk operations without formatting the drive. Simply install a partition manager solution on your PC and then you can use it to shrink one HDD without formatting it.
For this procedure, I recommend using MiniTool Partition Wizard. Download and install the application, then right click the partition you want to split and select Split.
This is how it looks:
yes you can,but I'll recommend to use windows in a free partition.
What I'd do just to be safe is back up your data, format your drive, install Windows, and then move your data back onto the drive