What Is Blockchain?
Blockchain is a distributed database that stores records in cryptographically linked blocks forming a chain. Unlike a traditional database managed by one entity, blockchain is replicated across thousands of computers (nodes) simultaneously.
Simple analogy: Imagine a ledger whose copies are held by 10,000 people. To alter one record, you would have to change it in more than half the copies simultaneously — a practically impossible task.
## Three Core Components
1. Block — Contains a set of transactions, a timestamp, and the 'hash' of the previous block. A hash is a digital fingerprint: the smallest data change produces a completely different hash.
2. Chain — Each block references the hash of the previous block. If someone alters Block #500, its hash changes, invalidating Block #501, and so on to the end of the chain.
3. Consensus — The mechanism enabling thousands of mutually untrusting nodes to agree on the same version of history.
- Proof of Work (PoW): nodes compete to solve math puzzles. Used by Bitcoin.
- Proof of Stake (PoS): nodes selected based on staked crypto. Used by Ethereum since 2022.
## Real Example
Walmart uses blockchain to trace food products from farm to store shelf. When a contamination outbreak occurs, the source can be found in 2 seconds — a process that previously took 7 days.
Key applications: financial records, supply chains, medical records, voting, academic certificates, and smart contracts.