New
#101
Take a look in Disk Management after you restart with the Seagate connected.
It will probably be noted as a "primary" partition, but not much else.
Your boot drive will probably be listed as primary, boot, system, active, and maybe page file and crash dump.
If your boot drive is brand new, you might want to copy your personal files from the Seagate to the boot drive rather than move them. There is some chance your new drive will fail and they tend to fail early. If it makes it through the first few hundred hours, it has a good chance of lasting a long time---at which point you can delete the stuff from the Seagate.
I'd choose some type of backup software to copy your personal files periodically from the new drive to the Seagate.
You can also consider using images to back up Windows, but I wouldn't rely on images as a backup for my personal files.
I'd look at System Restore and set a limit on how much space you want it to take up. It can gobble up a lot of space if you don't set a limit.
Get a good antivirus going and make sure Windows is updated.