A blockchain is a digital ledger, or record book, that is shared across many computers instead of being stored in one central location. Every new set of transactions is grouped into a block, and each block is linked to the one before it, forming a chain that stretches back to the very first transaction ever recorded.
What makes blockchains unusual is how they handle trust. Rather than relying on a single company or government to keep an accurate record, thousands of independent computers, called nodes, each keep their own copy and agree on which transactions are valid. To change old records, an attacker would need to alter the majority of these copies simultaneously, which becomes extremely difficult as the network grows.
This design is what allows cryptocurrencies to function without a central bank. Bitcoin's blockchain, for example, simply records who sent how many coins to whom, and that record is visible to anyone who wants to check it.
Frequently Asked Questions
Is blockchain the same thing as Bitcoin?
No. Bitcoin is one application built on top of a blockchain. Blockchain itself is the underlying technology, and it has since been used for many other cryptocurrencies and applications beyond just payments.
Can blockchain records be deleted?
In practice, no, once a transaction has enough confirmations behind it. The further back a transaction is in the chain, the more computing power it would take to rewrite history, which makes older records effectively permanent.
