I was now copying a folder which contains thousands of small files (about 3-4 KB each) from my laptop to my external hard disk. The whole folder should be around 40 MB. However, I noticed the process took quite long (about half an hour on USB 3.0).
So, I went to check the copied folder's size using Explorer (Windows 10 by the way), and to my surprise the folder properties shows "Size: 40 MB"; "Size on disk: 5 GB", as seen in the screenshot below.
Any explanation to why is this happening? Is this normal? By the way, my hard drive still has about 250 GB left, so it's not really running out of storage space, if this is of any relevance.
Edit: I do (kind of) know the difference between size and size on disk, just asking if it is normal for the difference between them to be this big (from 40 MB to 5 GB).