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block in a blockchain

What is a block in blockchain? 📖

A block is a data structure in the blockchain database where records of transactions in a cryptocurrency are stored permanently.

The concept of these blocks was presented by an anonymous person, Satoshi Nakamoto, in 2008. It is important to note that Satoshi is also the creator and founder of Bitcoin. His idea was that each block in the chain must contain the address of other blocks and they are chained with each other thus forming a blockchain.

How do individual blocks of information form a chain?

A block is a permanent, immutable record of a transaction that can never be changed or removed once a transaction is added.

A new block is created when a new transaction is entered and validated on the chain. Once the transaction is validated, it gets closed and then only a new one is created for a transaction.

The first block in a chain is the genesis block which happens to be the only one that doesn’t contain data of the previous hash because it’s the first in the chain.

Moreover, it can be identified by its cryptographic hash, which is a digital fingerprint made by hashing the block header twice in the Secure Hash Algorithm (SHA-256). The resulting 32 byte hash is called a hash.

The hash of the first Bitcoin block ever created looks like this 👇🏼


Blocks store a lot of pieces of information which include 👇🏼

  • A list of transactions that have been recorded
  • The number of transactions
  • The size so that only a specific amount of information is stored
  • A number that contains values and can be used to identify the block as a part of a cryptocurrency’s network

Blocks ensure that attacking a blockchain becomes virtually impossible because there is no central ledger to hack. Thus their function and presence makes a blockchain very secure.