BitTorrent in itself is only a file-downloading protocol. In BitTorrent, files are split up into chunks (on the order of a thousand per file), and the downloaders of a file barter for chunks of it by uploading and downloading them in a tit for tat like manner to prevent parasitic behavior. Each peer is responsible for maximizing its own download rate by contacting suitable peers, and peers with high upload rates will with high probability also be able to download with high speeds. When a peer has finished downloading a file, it may become a seed by staying online for a while and sharing the file for free, i.e., without bartering.