Nodes & software

A full node is what makes bitcoin's rules real. Every node independently verifies every block and every transaction against the consensus rules and rejects whatever fails, which is why nobody can spend coins they do not have even when a miner would happily help them.

Running one changes your relationship with the network. A wallet that queries somebody else's server trusts that server to tell the truth about your balance, and to not keep a log of which addresses you asked about. A wallet backed by your own node does neither. That is the practical reason nodes keep coming up in privacy discussions that look at first like they are about something else.

The section covers the software itself. Bitcoin Core is the dominant implementation and the de facto specification. Alternative implementations exist and matter, and the entries here are honest about the risk of running one. Pruning lets a node validate everything and then discard old blocks, which is what makes a full node practical on a laptop. Initial block download is the wait before any of it works.

RPC, the peer to peer message types that tie nodes to each other, and the sync strategies they use to catch up are here too, for the point where curiosity turns into a config file.