Terminology

• In the BitTorrent protocol, a file available for download is called a "torrent." A copy of that file available for download is called a "seed." While that copy is downloading, it is "seeding," and the file owner is "seeding" it. A computer that has a partial copy of a torrent available for copying is called a "peer." A person who downloads a file and then deletes it from his client so no one else can copy it, is called a "leech" or a "leecher."
  
  

Process

• A downloader finds details of a file to download and copies a torrent file that describes the file. Loading this into the Torrent client, cause that program to contact a tracker listed in the torrent file. The tracker contains a list of the IP addresses of the computers registered as holding copies of that file. The downloader then contacts those owners and requests a pert of the file. This process continues until the entire file is downloaded. Once the first block has downloaded, the client registers its address with the tracker as a source of part of the file. When the download completes, the client registers itself as a source for the entire file.
  
  

Seeder Benefits

• Seeding a file with BitTorrent rather than uploading it with any other file sharing system has distinct advantages. Each file is treated as though it were cut into segments and downloaders only request one segment at a time. This reduces the burden on the seeder who might have a large file available for other to download. That seeder does not have to wait until someone has downloaded the whole file, just a chunk. Once that downloaded has completed copying a block of the file, the downloader becomes an alternative source for that block, and so relieves the load on the one original source of the file. As more people download copies of the file, the requests from the original source reduce dramatically.
  
  

Downloader Benefits

• A downloader does not get locked into dependence on one source for a file. In the traditional file sharing model, once a file begins downloading, it could take weeks to complete if the uploader goes offline. Worse still, the uploader might delete the file before the download completes. Downloaders in BitTorrent systems can find segments of the same files in many locations and copy several blocks simultaneously, thus speeding up the download process.