What Is a Blockchain?
Reviewed and updated September 14, 2026 by the SmartCryptoEarnings editorial team · editorial policy
A blockchain is a shared database that many independent computers maintain together. Transactions are grouped into blocks, each block references the one before it, and the resulting chain is extremely difficult to rewrite because doing so would mean redoing all the work that followed.
Understanding blocks and confirmations is the fastest way to make sense of pending transfers, fee spikes and the word 'finality'.
Blocks, chains and why rewriting is hard
Each block contains a batch of transactions plus a cryptographic fingerprint of the previous block. Change any earlier transaction and every fingerprint after it breaks, so an attacker would have to out-produce the rest of the network to make a competing history stick.
This is why a transaction becomes safer the more blocks are built on top of it. Those additional blocks are what wallets and exchanges call confirmations.
Consensus: who gets to add the next block
Networks need a rule for choosing who writes the next block. Proof of work asks participants to spend computing power; proof of stake asks them to lock up the network's own asset and penalizes misbehavior. Both aim at the same goal, which is making dishonest history expensive.
- Bitcoin uses proof of work.
- Ethereum moved from proof of work to proof of stake in 2022.
- Different consensus designs produce different block times, fee behavior and finality guarantees.
What decentralization actually buys you
Decentralization means no single operator can quietly change balances, censor a payment or switch the system off. The cost is that there is no administrator to appeal to, throughput is limited compared with a centralized database, and upgrades require broad agreement.
Public, permissioned and 'blockchain' in name only
Public blockchains let anyone read the ledger and submit transactions. Permissioned ledgers restrict who can participate and are closer to a shared corporate database. When a product markets itself as blockchain-based, the useful question is whether anyone outside the company can independently verify the records.
Practical limits worth knowing
- Block space is finite, so fees rise when demand exceeds capacity.
- Confirmation times vary by network and by the fee you attach.
- Data written to a public chain is visible to everyone, permanently.
- Nothing on-chain verifies claims about the real world; that still depends on trusted parties.
Frequently Asked Questions
How many confirmations are enough?
It depends on the network and the amount at stake. Exchanges publish their own requirements, and larger transfers conventionally wait for more confirmations than small ones.
Can a blockchain be hacked?
Rewriting a large public chain's history is extraordinarily costly, but applications built on top of a chain, bridges and individual wallets are regularly compromised. Most losses happen at those layers, not in the base ledger.
Sources
Spotted something out of date? See our corrections policy and fact-checking policy.
Continue reading
Educational information only. Nothing here is financial, legal or tax advice.