A block is a container that holds data. Each block gets a unique hash — like a fingerprint — that identifies it.
Each new block stores the previous block's hash. This creates a link — like pieces clicking together. Block 2 references Block 1's hash (A1B2), connecting them.
If Block 1 changes, its hash changes, breaking the link. This is how blockchains detect tampering.
Add more blocks, each referencing the one before it. This creates a chain. The word "blockchain" describes this structure: a chain of blocks linked by cryptographic hashes.
Every block depends on all blocks before it. Change one block, and every block after it breaks.
Instead of one central computer holding the blockchain, many computers (nodes) each keep a complete copy. When a new block is added, all nodes receive it and update their copy.
This distribution makes the blockchain resilient — no single point of failure.
When people make transactions (sending money, recording data), these transactions go into a waiting pool. Miners collect pending transactions and pack them into a new block.
The block's data field holds these transactions, creating a permanent record.
Mining is solving a puzzle: find a nonce (random number) that makes the block's hash start with zeros. Miners try thousands of nonces per second.
First miner to find a valid hash wins the right to add the block to the chain. This work secures the network.
Sometimes two miners create blocks at the same time, creating competing chains. Nodes follow the longest valid chain — the one with the most work.
This consensus mechanism ensures all nodes agree on a single version of truth, even without a central authority.
Try to change data in an old block, and its hash changes. This breaks the link to the next block, which breaks the next, and so on — the entire chain after the change becomes invalid.
To fake a change, you'd need to re-mine every block after it faster than the network adds new blocks. Practically impossible.
Anyone can verify a blockchain's integrity by checking each block's hash and confirming it matches the "previous hash" in the next block. Follow the chain from start to end.
Every node continuously verifies new blocks before accepting them. Invalid blocks are rejected by the network.
Distributed: Many nodes hold identical copies
Linked: Blocks reference previous hashes, creating an unbreakable chain
Verified: Nodes check every new block's validity
Immutable: Past records cannot be changed without detection
Trustless: The system works without needing to trust any single party
This is how blockchains create tamper-proof, distributed records — no central authority required.