Blockchain Basics: Blocks, Nodes, and Consensus

A blockchain is a replicated state machine: many participants (nodes) hold a copy of the ledger and run the same rules to validate new updates. Transactions are grouped into blocks; each block references the previous block with a hash, producing a tamper-evident chain.

Consensus mechanisms

Consensus determines which chain is considered canonical. Widely used mechanisms include:

• Proof of Work (PoW) — miners expend computational effort to propose blocks (Bitcoin uses this).
• Proof of Stake (PoS) — validators lock tokens and are selected to propose/attest; misbehavior can be penalized by slashing.

Different designs trade off decentralization, security, and scalability. Layer 2 solutions (rollups, channels) move many operations off the base layer to increase throughput while settling security to the base chain.