Block

In short, a block is a computer file that stores transaction data. These blocks are arranged in a linear sequence that forms a continuous chain of blocks, which is where the term blockchain comes from.

Each new block is connected to the previous one through cryptography. The chain of linked blocks stores all the transaction data generated since the launch of a particular blockchain, so the records go all the way back to the first block, known as block zero or the genesis block. The number of confirmed blocks since the genesis block is called the block height.

Taking the Bitcoin blockchain as an example, each block is made up of several elements. A Bitcoin block typically contains a list of recent transactions, a timestamp, and a reference to the block that came right before it. This reference is a cryptographic hash of the previous block’s data. Because each new block includes the hash of the one before it, the blocks become cryptographically linked. This structure helps create a secure database that is highly resistant to tampering.

The block hash acts like an identifier. It is unique to each block and is produced through a process called mining. The block hash is the solution to a complex mathematical problem, and the miner that finds a valid solution for the next block is granted the right to validate that block and the transactions within it. Since mining requires a significant amount of computational resources, successfully mined blocks can produce new bitcoins as a way to reward miners for their work.

Sometimes two or more miners may find a valid block hash at almost the same time, so two different blocks are broadcast to the network. This can lead to two competing chains. To resolve this, the participants of the network, known as nodes, tend to follow the chain that eventually becomes the longest, meaning the one with more accumulated work. The other chain is then discarded, and its blocks become stale blocks.

Although blocks are usually discussed in the context of cryptocurrency transactions, they may also store other types of digital data on a blockchain technology system.

Learn more: What Is Blockchain and How Does It Work?