The testnet is an alternative Bitcoin block chain, to be used for testing. This allows application developers or bitcoin testers to experiment, without having to use real bitcoins or worrying about breaking the main bitcoin chain.
- Instead of ports 8333 (listen) and 8332 (JSON-RPC), ports 18333 and 18332 are used.
- Bootstrapping IRC channel is #bitcoinTEST instead of #bitcoin (both on irc.lfnet.org). The built-in node list is disabled.
- A different value of ADDRESSVERSION field ensures no testnet BitCoin addresses will work on the production network. (0x6F rather than 0x00)
- The protocol message header bytes are shifted up (0xFABFB5DA instead of 0xF9BEB4D9)
- Minimum difficulty of 1.0 on testnet is equal to difficulty of 0.5 on mainnet. This means that the mainnet-equivalent of any testnet difficulty is half the testnet difficulty.
- A new genesis block
Testnet uses a different genesis block to the main network. You can find it at http://blockexplorer.com/testnet/rawblock/0000000224b1593e3ff16a0e3b61285bbc393a39f78c8aa48c456142671f7110