What is a node in blockchain?

A node is essentially a program running on a single computer that allows you to connect with the rest of the blockchain network. It connects with other nodes to send information back and forth, checks that transactions sent between people are valid, and stores important information about the state of the blockchain.

In particular, one of the peculiarities of a blockchain network is that the network is essentially composed of only nodes: that is, the physical hardware running a blockchain such as Ethereum or Bitcoin is just the collection of all the nodes around the world being run by individual people. There's no master server or single source of truth - that's why it's decentralized!

There's typically two main categories of nodes - light nodes and full nodes. Light nodes sync just the block headers and request from full nodes for many queries, while full nodes keep the entire state of a blockchain - every transaction that's ever been created. Most queries work with light nodes, but full nodes are the backbone of the blockchain - they’re necessary to serve most information.

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