Block Definition in Crypto

A block is a file of data that records a batch of transactions on a blockchain. Blocks are arranged in order, with each new one attached to the one before it, which is why the whole system is called a blockchain. 

Purpose in a blockchain

Blocks keep the ledger organized and make the history of activity easy to verify. By chaining blocks together, the network preserves a complete record from the very first block, called the genesis block. The count of blocks since that first one is known as block height. 

What a block contains

Most block designs split data into two parts: a header and a body. The header stores metadata such as a timestamp, a unique identifier, and a reference to the previous block. The body lists the verified transactions bundled into that block. Exact layouts differ across chains. 

How blocks link together

Each block carries a cryptographic hash. That hash serves like a fingerprint for the block’s contents and also points back to the hash of the previous block. If someone tried to change data, the hash would change and the chain would no longer line up, which makes tampering obvious. 

How a new block gets added

After transactions are checked, a node proposes a block and broadcasts it. Other nodes verify it, and once accepted, the block is added to the chain with its hash linking back to the prior block. This process creates the linear, append-only history that blockchains are known for. 

Consensus and who adds blocks

Blockchains rely on a consensus mechanism to decide which proposed block becomes the next official one. In proof of work, miners compete to find a valid hash that satisfies network rules, and the winner earns the right to add the block and take the reward. In proof of stake, validators are chosen based on stake and follow protocol rules to finalize blocks. Both models aim to keep the ledger consistent across the network.

Block size and limits

Block size varies by chain. For example, the Bitcoin network uses an effective limit equal to 4 MB of block weight, while other networks choose different limits to handle more data per block. The chosen limit affects throughput and how quickly blocks propagate.

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