A Bitcoin node is a computer that runs Bitcoin software and participates in the network by verifying and relaying data. Not every node mines, but every node that follows the rules helps keep the system honest.
Here is what nodes do:
- Maintain a copy of the blockchain
Nodes download and store the current blockchain or at least the parts they need. This lets them independently verify transactions and blocks. - Validate transactions
When nodes receive a transaction, they check:
- Are the inputs valid unspent outputs?
- Are the signatures correct?
- Do the amounts add up?
If a transaction breaks the rules, they reject it and do not relay it further.
- Are the inputs valid unspent outputs?
- Validate blocks
When a miner broadcasts a block, nodes verify the proof of work and every transaction inside. Only if the block is valid do they attach it to their chain and pass it on. - Relay data
Nodes relay valid transactions and blocks to their peers. This helps the network stay connected and up to date.
There are different types of nodes:
- Full nodes: Store and validate the whole chain.
- Pruned or simplified nodes: Store only part of the data, or use proofs from full nodes, to reduce storage needs.
- Mining nodes: Full nodes that also construct blocks and compete in proof of work.
Running a node gives you direct insight into the network and lets you verify that the rules are being followed, rather than trusting someone else’s copy of Bitcoin.