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How does a blockchain work?

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Quick answer

A blockchain works as a shared digital ledger duplicated across many computers, where records are grouped into 'blocks' chained together cryptographically. Because everyone holds a copy and each block locks in the previous one, the record is extremely hard to tamper with.

Step by step

Transactions are grouped into blocks and added in order.
Each block is cryptographically linked to the one before it.
Copies of the ledger are stored across many computers (decentralized).
Changing an old record would break the chain and be rejected.
It enables trust without a central authority.

People also ask

What makes a blockchain secure?

Each block is cryptographically tied to the previous one and copied across many computers, so altering a record breaks the chain and is rejected by the network.

Why is a blockchain called 'decentralized'?

No single party holds the master copy — the ledger is duplicated across many independent computers that must agree on it.

What is a blockchain used for?

Cryptocurrencies, but also supply-chain tracking, digital contracts, and records where tamper resistance and shared trust matter.

Why can't blockchain records be changed?

Changing one block alters its hash, which breaks every block after it — and a majority of the distributed network would have to accept the change.

What is a hash?

A fixed-length fingerprint of data; any change to the data produces a completely different hash.

What is consensus?

The process by which the network's computers agree on which new block is valid before adding it to the chain.