How BitTorent works

The usual method of transferring files on the internet is the "client-server" model where a central server sends the entire file to the computers that request it.

BitTorrent is also a method for transferring files although it uses peer-to-peer technology to transfer large files more quickly.




I am now going to show you how it works in an extremely simplistic manner. For this example imagine the file is broken into 3 blocks, A, B and C

- The torrent maker starts with the whole file.
- Person 2 connects and downloads block A from the torrent maker
- person 3 connects and downloads block B from the torrent maker
- Person 2 sends block A to person 3 while person 3 sends block B to person 2 and The torrent maker is sending block C to both.

You can see that the torrent maker only sent out the whole file once. After this when more people start to download the file they download pieces not only from the torrent maker but also from each other.

Now for some commonly used terms (these definitions are taken from bittorrent.com:

client the BitTorrent software used to download and upload files. The BitTorrent client can be downloaded here.
block A block is a piece of a file. When a file is distributed via BitTorrent, it is broken into smaller pieces, or blocks. Typically the block is 250kb in size, but it can vary with the size of the file being distributed. Breaking the file into pieces allows it to be distributed as efficiently as possible. Users get their files faster using less bandwidth.
seeder/seeding a peer that is done downloading a file and is now just making it available to others.
leech or leecher usually refers to a peer that is downloading while uploading very little, or nothing at all. Sometimes this is unintentional and due to firewall issues. The term leech is also sometimes used to simply refer to a peer that is not seeding yet.

I personally use Utorrent which is a full featured yet light weight client. Download it here