Network Architecture: Nodes, Clients, and Sync

When people say "blockchain is decentralized," what they mean concretely is that the network is composed of many independent computers, called nodes, each running the same software and maintaining the same shared state. The properties of decentralization, censorship resistance, and trust-minimization come from the fact that no single party operates these nodes. They are run by individuals, companies, miners, exchanges, governments, and many others, distributed worldwide. A "node" in blockchain context is simply a computer running the network's software (like Bitcoin Core for Bitcoin, or Geth/Nethermind/Erigon for Ethereum). The node maintains a copy of the blockchain, validates new blocks and transactions according to the protocol rules, and relays them to other nodes. There are different types of nodes with different responsibilities: • **Full nodes** validate every block and every transaction independently, maintaining a complete copy of the blockchain. They are the backbone of decentralization. • **Mining/staking nodes** are full nodes that also participate in block production. They earn rewards. • **Archive nodes** are full nodes that additionally retain all historical state at every block height (rather than just the current state). Used for analytics and historical queries. • **Light clients (SPV nodes)** store only block headers and rely on full nodes for verification via Merkle proofs. Mobile wallets are typically light clients. • **Pruned nodes** validate everything but only retain recent blocks, deleting old data to save disk space. Modern Bitcoin Core can run as a pruned node with as little as 5 GB of disk. As of May 2026, Bitcoin has approximately 18,000 to 22,000 reachable full nodes worldwide (Bitnodes data), plus many more unreachable ones (behind firewalls, NATs, or Tor). The U.S. hosts about 10 percent of reachable nodes; Germany, France, Netherlands, Russia, and Canada round out the top of the list. Ethereum has approximately 13,900 unique node IPs, primarily running Geth, Nethermind, Reth, Besu, and Erigon clients. The number of nodes matters because more nodes means more independent verification, harder censorship, and more places where an honest copy of the chain exists. A blockchain run by ten cooperating nodes would be technically a blockchain but functionally a permissioned database. A blockchain with twenty thousand independent operators is much harder to compromise.