Blockchain
A blockchain is a shared record of cryptocurrency transactions that miners secure by adding verified blocks.
Definition
A blockchain is a public record of transactions grouped into blocks and linked together in order. In cryptocurrency mining, miners compete to add the next valid block to this record, and each block points back to the block before it.
How It Works
When users send cryptocurrency transactions, those transactions wait to be confirmed by the network. Miners collect valid transactions from the mempool and assemble them into a candidate block.
The miner then builds a block header. The header includes a reference to the previous block, a summary of the new transactions, the current difficulty target, and a nonce that miners can change.
In proof-of-work systems such as Bitcoin, mining means hashing the block header over and over. A valid block must produce a hash below the network’s target, which is controlled by mining difficulty. Because hash results are unpredictable, miners use hash rate to make many attempts quickly.
When a miner finds a valid block, it broadcasts it to the network. Other nodes check the transactions, verify the proof of work, and confirm that the block correctly links to the chain.
If accepted, the block becomes part of the blockchain. The successful miner earns the block reward, which can include new coins and transaction fees.
Why It Matters
The blockchain is the shared history that lets a cryptocurrency operate without a central bookkeeper. Everyone can verify the same record, but no single miner can simply edit it.
For miners, the blockchain defines what they are competing to extend. A miner is trying to produce the next block that the network will accept.
The chain structure also protects older transactions. Since each new block depends on the previous block’s hash, changing an old block would also change every block after it. An attacker would need to redo the proof of work and catch up with the honest network.
This is why confirmations matter. A transaction buried under several later blocks is much harder to reverse.