A shared, append-only ledger
A blockchain is a database that many independent computers keep a copy of. New data arrives in batches called blocks. Every block stores the hash of the previous block, so the blocks form a chain in a fixed order.
- •Append-only: you add blocks, you never edit old ones.
- •Replicated: thousands of nodes hold the same history.
- •Verifiable: anyone can re-check every block from genesis.
Hashes are the glue
A cryptographic hash turns any input into a fixed-length fingerprint. Change one character and the fingerprint changes completely. Because each block header commits to the previous hash, editing an old transaction would invalidate every block after it.
Nodes, clients and explorers
A node validates and stores the chain. A wallet or dApp usually talks to a node through an RPC endpoint instead of running one. Block explorers are just friendly front-ends over the same public data.
- •Full node: validates everything, stores state.
- •RPC provider: hosted node your wallet calls.
- •Explorer: read-only UI (Etherscan, Solscan, mempool.space).