I use Internet Download Manager (IDM) for downloading data, and I have noticed that in it's download progress window, it shows whether or not a download is pause-able (resume-able). Typically, file-sharing sites do not allow the transfer to be resumed if the connection is broken.
So the question is this: how does this work? Is it some config that's done on the sever? How does this differ from torrent downloads, where the download is always resume-able.