The Bitcoin Network

One of the core components of the Bitcoin system is the peer-to-peer network that it runs on. While peer-to-peer, or P2P, networks existed before Bitcoin, understanding what is happening on the Bitcoin P2P network is fundamental to understanding Bitcoin. 

To grasp what is happening on the Bitcoin network, read this chapter that discusses what the computers, or nodes, on the Bitcoin network are doing. It covers node functions such as running a wallet, mining, maintaining a copy of the blockchain, and routing. We'll get more in-depth on wallets and mining in later sections. Here you'll want to focus on the last two functions mentioned, maintaining a record of all transactions made on the network by keeping copies of all blocks in the blockchain and validating and propagating transaction data.

Full Nodes

Full nodes are nodes that maintain a full blockchain with all transactions. More accurately, they probably should be called "full blockchain nodes". In the early years of bitcoin, all nodes were full nodes and currently the Bitcoin Core client is a full blockchain node. In the past two years, however, new forms of bitcoin clients have been introduced that do not maintain a full blockchain but run as lightweight clients. We’ll examine these in more detail in the next section.

Full blockchain nodes maintain a complete and up-to-date copy of the bitcoin blockchain with all the transactions, which they independently build and verify, starting with the very first block (genesis block) and building up to the latest known block in the network. A full blockchain node can independently and authoritatively verify any transaction without recourse or reliance on any other node or source of information. The full blockchain node relies on the network to receive updates about new blocks of transactions, which it then verifies and incorporates into its local copy of the blockchain.

Running a full blockchain node gives you the pure bitcoin experience: independent verification of all transactions without the need to rely on, or trust, any other systems. It’s easy to tell if you’re running a full node because it requires more than one hundred gigabytes of persistent storage (disk space) to store the full blockchain. If you need a lot of disk and it takes two to three days to sync to the network, you are running a full node. That is the price of complete independence and freedom from central authority.

There are a few alternative implementations of full blockchain bitcoin clients, built using different programming languages and software architectures. However, the most common implementation is the reference client Bitcoin Core, also known as the Satoshi client. More than 75% of the nodes on the bitcoin network run various versions of Bitcoin Core. It is identified as "Satoshi" in the sub-version string sent in the version message and shown by the command getpeerinfo as we saw earlier; for example, /Satoshi:0.8.6/ .