Blockchain

A blockchain is a distributed, append-only ledger: data — most often transactions — is grouped into blocks, and every block stores a cryptographic hash of its predecessor. Altering any historical entry would change its hash and break the link to every later block, so tampering is immediately detectable. Because the ledger is replicated across many independent nodes rather than kept on one server, no single participant can rewrite history on their own.

How a blockchain works

Participants run nodes that hold a copy of the chain and exchange new transactions peer-to-peer. Pending transactions are gathered into a candidate block, which the network accepts through a consensus mechanism:

• Proof of Work — miners compete to solve a computational puzzle; forging history would require outcomputing the honest majority,
• Proof of Stake — validators lock up capital and are penalized for dishonesty, cutting energy use by orders of magnitude,
• permissioned consensus — in consortium networks (e.g. Hyperledger Fabric), a known set of organizations signs blocks, trading openness for throughput.

Unlike a conventional database, where an administrator can update or delete rows, a blockchain only ever grows. Replication happens without any primary server, and smart-contract platforms such as Ethereum extend the ledger with code that executes deterministically on every node.

Practical use

Cryptocurrencies remain the flagship application, but the same properties — shared state, tamper evidence, no central operator — are used for supply-chain provenance, document timestamping, digital identity, asset tokenization and settlement between institutions that do not fully trust one another. Enterprises typically choose permissioned chains, where regulators or auditors can be given read access to a single authoritative record.

It is worth being sober about the trade-offs: blockchains are slower and more expensive to run than ordinary databases, and most projects labeled "blockchain" would work better without one. Operating a full node of a public network is itself an infrastructure task — chains grow into terabytes, so nodes need fast NVMe storage, ample bandwidth and reliable uptime, which is why they are commonly hosted on dedicated servers or a capable VPS.