My External Hard Drive is half filled, but why is it 99%

[asem1123]

My external hard drive is 1TB and I've been doing almost everything on it because my laptop only has a 250GB SSD. I saw it's only 13GB free of 933GB, so I Ctrl + A right click properties to check the files but it only says 440GB used (including Windows backup, and I've already gained access to it), so what gives? Does anyone know what the extra 500GB is or is it a normal NTFS thing, or how can I get rid of it if it's useless?

https://imgur.com/a/YGOVCW3

 

[USAFRet]

Install either WinDirStat or WizTree
Run as Administrator, selecting only the drive in question.

Post a screencap here.

 

[asem1123]

Oh, I guess it's the WindowsImageBackup then.

https://imgur.com/a/WuTMBx1