Blockchain is a cryptographically secured, distributed ledger linked in a chain of blocks. Each block contains: the previous block's hash, transactions, a timestamp, and a nonce. The SHA-256 hash function means changing one character changes the entire hash. This guarantees immutability.
Consensus mechanisms: Proof of Work (Bitcoin — energy-intensive computation race), Proof of Stake (Ethereum 2.0 — staking assets, saving energy). Smart contracts are automatically executing conditions written as code. Real applications: supply chain tracking, certificates, voting systems. Cryptocurrency is one application of blockchain, not the technology itself.
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