Autosave: 2024-08-09 17:00:03

zk/Torrenting.md

@@ -17,4 +17,53 @@ to others.
 
 ## Procedure
 
-Large files are divided into small
+Large files are divided into small equal sized pieces and each piece is assigned
+a unique hash identifier. The `.torrent` file details the number of pieces,
+their sizes and hash values.
+
+Clients request different pieces from different peers simultaneously. As pieces
+are received, they are verified against their hash. Corrupted or incorrect
+pieces are discarded and re-downloaded.
+
+The client software reassembles the pieces in the correct order and the final
+file will be identical to the original which can be verified by comparing
+hashes.
+
+## Key terms
+
+- _tracker_
+  - a server that coordinates communication between peers (so there is a server
+    but its role is more lightweight than client-server, coordinating the peers
+    rather than hosting or distributing file content)
+- _swarm_
+  - a group of peers sharing the same file
+- _seeding_
+  - uploading file pieces to other peers
+- _leeching_
+  - downloading file pieces from other peers
+
+> An alternative to a tracker server is to use trackerless methods such as
+> distributed hash tables
+
+## Terminological clarification
+
+- _BitTorrent_ is the communications [protocols](Network_protocols.md) for P2P
+  file sharing. It was also a client software developed by the company
+  BitTorrent Inc.
+
+- _torrenting_ is the general terms for that act of sharing files using the
+  BitTorrent protocol
+
+## Napster
+
+Napster pre-dated the emergence of the BitTorrent protocol. It did not segment
+files and files were downloaded directly from peers. It was a centralised P2P
+network because there was a central server that indexed all available files
+which kept a database of all connected users and their files.
+
+When you searched Napster you would be querying this DB on the server. The
+server would facilitate a direct connection between the consumer and provider
+peer for the data exchange.
+
+When users share with BitTorrent the `.torrent` file is the source of truth and
+a swarm is created around the users who have possess the file.