Before formatting an external hard drive on Windows, back up all the informational data like files, music and official data into safe place.
To format an external hard drive, plug in the device into system or a wall outlet.
After plug in hard drive into the system, you will get option to open Windows Explorer and by clicking on the computer section in the side bar, you will see your hard drive get attached to your system.
When you will do right click on the hard drive icon, you will get option to choose "Format"?.
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After that, you can opt any file system that you want to use for the operating systems.
Mention your hard drive with a name under Volume Label and check out the Quick Format box.
To initiate the formatting process, click on the start button and within a few seconds, you will get notification when the process get completed.
Open the hard drive in Windows Explorer and start dragging documents and files into it.
Follow the stepwise procedure to format an external hard drive and make sure it will not show similar free space as it displays on the box as the systems determine the space differently as it is marked on the box.