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- Size is the actual size of the file or the folder. So if you were to transfer the file or folder to another drive, CD, DVD or USB drive, this would be the actual size in bytes that is being copied.
Size on disk means the size that is being taken up on the disk (your hard drive).
Generally, Size on disk will be larger than Size.
- However, sometimes, due to built in compression, the file is actually smaller on the disk. A file can also appear to be smaller on disk if the file is a sparse file. In that scenario, file size refers to the logical size of the file, whereas size on disk refers to the physical size of the sparse file.
https://superuser.com/questions/518414/how-can-the-size-on-disk-be-smaller-than-size
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