Detailed answer
A blockchain is a shared database across many computers where records are linked in a chain — making history tamper-evident. No single party controls it. Once recorded, data cannot be altered without network consensus. Blockchain is slower and more expensive than a regular database, but provides multi-party trust that a single database cannot.
Q1: What is a blockchain?
A database that is shared across many computers (nodes), where each record is linked to the previous one in a chain — making the history tamper-evident. No single party controls it. Once a record is added, it cannot be altered without every node in the network detecting the change.
Q2: How is blockchain different from a regular database?
A regular database is controlled by one entity — who can modify any record. A blockchain is controlled by a distributed network — no single entity can modify a committed record without consensus from the rest. The trade-off: blockchain is slower and more expensive; the gain is multi-party trust.
Q3: What is a node?
A computer that participates in a blockchain network — storing a copy of the ledger and validating transactions. Public blockchains (Ethereum, Bitcoin) have tens of thousands of nodes. Private enterprise blockchains have a defined set of nodes, one per participating organization.
Q4: What is a block?
A batch of transactions grouped together and added to the blockchain. Each block contains: a list of transactions, the hash of the previous block (the 'chain' link), a timestamp, and a nonce (proof of work) or validator signature (proof of stake).
Q5: What is a hash?
A fixed-length string produced by running data through a cryptographic function (SHA-256 for Bitcoin, Keccak-256 for Ethereum). The same input always produces the same output. Any change to the input produces a completely different output. This property makes hashes useful for detecting tampering: if a record changes, its hash changes, breaking the chain link to the next block.