Heya,
If the HDD you're referring to is an external drive, taking it out of the enclosure and then plugging it internally into a computer, it will be recognized by your OS based on whether or not it is FAT, FAT32, or NTFS (or other options). If it's already formatted as NTFS and has been used as such, it will function as a physical drive and will be assigned a drive letter. It will not appear as a removable disk or anything. It will appear in My Computer (or non-windows equivalent to that) as a physical hard drive with a drive letter assigned.
Very best,