This allows clients to resume an interrupted download (or download multiple parts simultaneously) without having to re-download the entire resource again. HTTP/1.1 allows for clients to request pieces of a file instead of the entire thing. Now multi-threaded download managers (like the Free Download Manager or FDM you used) that work with direct HTTP links can also resume downloads and download multiple parts of a file simultaneously, provided certain server conditions are met. those not downloaded so far) are zero bytes that are filled in gradually by the client as each piece completes. So even though you might have 75% of a file, that doesn't mean it's a contiguous 75% data block from the beginning of the file.
In simple words, the problem arises due to the fact that torrent clients simultaneously download various pieces of each file and 'stitch' them together in the proper order on disk.
Theoretically this should be possible, but in practice there seems to no easy way to accomplish it (at least none that I know of).
