Crypto glossary
Archive node
An archive node is a blockchain node that keeps every historical state of the ledger, not only the latest one, so any past balance can be queried directly.
A standard full node validates the entire history but discards old intermediate states once they are no longer needed, keeping only recent data. An archive node keeps all of it: the balance of every account, contract storage and other state at every block height since genesis. That lets it answer questions such as what a wallet held at block 15,000,000 without replaying the chain.
Block explorers, indexers, analytics firms, tax tools and auditors depend on archive nodes, as do developers who need to trace old transactions. Most people never run one themselves; they reach archive data through RPC providers that charge for heavy historical queries.
Archive nodes need far more disk space than full nodes, several terabytes on Ethereum depending on the client, and take longer to sync. Newer clients such as Erigon and Reth store history more efficiently, but the cost means only a small number of operators run them, which concentrates access to historical data.
Example
A tax app needs a user's token balances on 31 December of past years, so it queries an archive node for the state at the last block of each of those days.