Blockchain
A blockchain is a decentralised ledger where transactions are stored in chronological, cryptographically linked blocks — the underlying structure of Bitcoin.
Blockchain is the invention that made Bitcoin possible: a distributed database without central administrator, where each new block is cryptographically linked to the prior one. Altering an old transaction would invalidate all subsequent blocks — practically impossible with thousands of nodes. The term is now broadly applied to non-Bitcoin systems, often without the same decentralisation principles.
Example
To forge transaction X in block 800,000 you'd need to recompute all ~40,000 subsequent blocks — beyond the full current Bitcoin network's compute. Historical transactions are practically immutable.
Frequently asked questions
How big is the Bitcoin blockchain?
In 2026 around 600-650 GB, growing ~80-100 GB per year. Pruned nodes can run on ~10 GB by trimming old block data.
Related terms
Further reading
- → Our service: Bitcoin sector
- → Blog: Bitcoin & YMYL: how Google judges crypto sites
- → Blog: Fintech: highest AI Overview exposure of all sectors
- → Blog: GEO for Bitcoin & fintech: why you need it