What Is a Blockchain, and How Does It Work in Bitcoin?
A blockchain is a type of distributed database that stores information in a sequence of blocks. In the context of Bitcoin, the blockchain is a public record of confirmed transactions that is maintained and independently verified by network participants.
Each block contains a group of valid Bitcoin transactions, along with other data required to connect that block to the existing chain.
The term blockchain comes from this structure: information is stored in individual blocks, and each new block is cryptographically linked to the previous one.
How are blocks connected?
Every Bitcoin block contains a reference to the previous block through its block header.
This reference is based on a cryptographic hash. A hash is a fixed-length output generated from data. If the underlying data changes, the resulting hash also changes.
Because each block refers to the previous block, changing historical data would break the links between blocks.
For example:
Block A → Block B → Block C
Block B contains information derived from Block A, and Block C contains information derived from Block B. This creates an ordered chain of historical records.
Who maintains the blockchain?
The Bitcoin blockchain is not stored on a single central server.
Instead, many independent nodes maintain copies of the blockchain and verify new transactions and blocks according to the same protocol rules.
When a new block is received, a node independently checks whether it follows Bitcoin’s consensus rules. A block that violates those rules is rejected, regardless of who created it.
This means that the validity of Bitcoin’s blockchain does not depend on trusting a single company, government, or database administrator.
How is new information added?
Bitcoin users create transactions that spend existing transaction outputs.
Before a transaction can become part of the blockchain, it must satisfy the network’s validation rules.
Valid transactions can be collected into a candidate block. Through Bitcoin’s Proof of Work process, blocks compete to become the next accepted block in the chain.
Once a valid block is accepted and additional blocks are built on top of it, reversing its transactions becomes increasingly difficult.
Why is the Bitcoin blockchain difficult to change?
The blockchain is often described as immutable, but this should not be understood as meaning that changing history is mathematically impossible.
Rather, changing confirmed historical data would require overcoming several mechanisms simultaneously:
The cryptographic links between blocks
The Proof of Work required to produce blocks
Independent validation by nodes
Competition from the rest of the network
An alternative version of the blockchain must still follow Bitcoin’s consensus rules. Nodes do not accept changes simply because a participant has modified a local copy of the blockchain.
A simple way to understand it
A traditional database is usually controlled and updated by a central administrator.
Bitcoin’s blockchain is different because multiple independent participants maintain and verify the same transaction history according to shared rules.
In simplified form:
Transactions → Validation → Block → Cryptographic link to previous block → Distributed verification
The result is a shared transaction history that can be independently verified without requiring participants to trust a central record keeper.
In Bitcoin, the blockchain is therefore best understood not simply as a chain of data blocks, but as part of a broader system combining cryptography, distributed validation, consensus rules, and Proof of Work.
