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What is blockchain?

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Quick answer

A blockchain is a shared digital ledger that records transactions across many computers so the record can't be changed retroactively. Each 'block' of data is cryptographically linked to the one before it, forming a tamper-evident chain. It's decentralized: copies live on many computers (nodes), so there's no single point of control or failure.

Key things to understand

  1. It's decentralized: copies live on many computers (nodes), so there's no single point of control or failure.
  2. Each block contains data, a timestamp, and a cryptographic fingerprint (hash) of the previous block.
  3. Changing one block would break every block after it, which is what makes tampering obvious.
  4. It underpins cryptocurrencies like Bitcoin, but also supply-chain tracking, digital identity, and smart contracts.

People also ask

Is blockchain the same as Bitcoin?
No. Bitcoin is one application of blockchain. The blockchain is the underlying technology that many other systems also use.
Why is blockchain considered secure?
Because records are distributed across many nodes and cryptographically chained, altering history would require controlling most of the network simultaneously.
What is a smart contract?
Code stored on a blockchain that runs automatically when conditions are met — for example, releasing a payment once a delivery is confirmed.