To download a specific piece of a file from a BitTorrent swarm, your client must interact with other peers through a series of structured messages. Core Download Process
: You can choose to download only specific files within a torrent by right-clicking them in your client and selecting "Don't Download" or "Skip" .
: Once all chunks for a piece are received, the client combines them and runs a SHA-1 hash check against the value provided in the .torrent file. If the hash matches, the piece is verified and saved to disk; if not, it is discarded. Technical Implementation & Optimization