Explainer

Building blocks of a blockchain

Updated 2026-02-10

A blockchain is literally a chain of blocks. Each block is a bundle of records — transactions, ownership changes, messages — plus a short fingerprint of the previous block. That simple idea is what makes the ledger so hard to rewrite.

What is inside a block

a list of transactions;
a timestamp;
the hash of the previous block;
data required by the consensus mechanism (for example, a nonce in proof of work).

Hashes as fingerprints

A hash function turns any data into a fixed-length string. Change one comma in the input and the hash changes completely. Because each block contains the previous block's hash, editing an old record would break every block after it — and the network would reject the forged chain.

Distributed ledger

The same copy of the ledger is stored by thousands of independent computers. To change history, an attacker would need to control most of them at once. This is why blockchains are attractive for records that many parties must trust: payments, supply chains and, increasingly, property titles.

Limits

A blockchain guarantees that a record has not been altered — not that it was correct in the first place. If wrong data is written, it stays wrong. That is why links between on-chain records and the real world, such as a land registry, matter so much.