What is a block in blockchain

What is a Block in Blockchain? A Quick Guide!

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What is a block in blockchain? Blocks make up the transactions in a blockchain. Transactions that have been added to the block cannot be reversed. Furthermore, once a block has been added to the chain, it cannot be changed. All information stored in blocks will remain there indefinitely as long as the blockchain exists. Blocks are stacked one on top of the other in a straight line. They form a chain, one by one, containing the entire history of network transactions.

This article will explain what is a block blockchain, what is stored in a blockchain block, and much more!

What is a block in blockchain?

In short, a “block” is a computer file that stores transaction data. These blocks are arranged in a linear sequence, resulting in an infinite chain of blocks, hence the term “blockchain.”

As a result, all information about blockchain transactions is gathered and recorded within these blocks, and each newly generated block is linked to the previous one using cryptographic techniques.

As a result, the records go all the way back to the first block, known as block zero or the “genesis block.”

LEARN MORE: What is a Genesis Block in Blockchain

What is stored in a blockchain block?

The chain of linked blocks contains all of the transaction data generated since the inception of a specific blockchain. One of the blockchain’s top priorities is to keep these records safe. A block, however, requires a few additional elements in order to function in a blockchain. But, before we get to that, let’s take a look at what’s stored in a blockchain block.

Cryptocurrencies got their name from the fact that they rely heavily on cryptography. The cryptographic principle used in the case of blocks is known as the hash function. A hashing algorithm determines a string of symbols known as a hash. Consider bitcoin, which employs the SHA-256 algorithm (but not all cryptocurrencies use the same algorithm). This algorithm transforms all of the data in a block into a unique string of symbols that serves as the block’s ID.

The block hash (the block header) is composed of the six elements that comprise a block:

  • The version number of the block,
  • The hash of the previous block in the chain,
  • A code generated from transaction data,
  • A timestamp of when the block was created,
  • The difficulty target that adjusts the difficulty of mining,
  • And a random string of characters called the nonce.

Except for the last of these, all of these elements are known in advance before a block is added to the chain. The nonce, on the other hand, remains a mystery. The goal of crypto mining is to determine the nonce. The miner who finds the nonce that meets the current difficulty requirement first adds the block to the chain, sealing it into the transaction history.

LEARN MORE: What is a Crypto Mining Pool? Is it Profitable

How Block is Created in Blockchain

In short, blocks are created when miners or validators successfully validate the encrypted information in the block header, causing a new block to be created.

LEARN MORE: Block Header in Blockchain Explained! How it Works

The hash of the previous block is always included in the generation of a new block, which is how the blocks are cryptographically linked. Such a structure enables the creation of a secure database that is highly resistant to tampering and attacks. The block hash functions as an identifier. It is unique to each block and is created through a process known as mining.

LEARN MORE: What is Bitcoin Mining? All You Need to Know

The block hash is essentially the solution to a complex mathematical problem, and the miner who finds a valid solution for the next block is granted the right to validate that block (and the transactions therein). Because mining requires a significant amount of computational resources, successfully mined blocks generate new cryptos to compensate miners for their efforts.

However, two or more miners may find a valid block hash at the same time, resulting in two distinct blocks being broadcast to the network. As a result, two competing chains are formed. To address this issue, network participants (nodes) will select the chain that eventually becomes the longest (with the most “accumulated work”). The other chain is then removed, and its blocks become obsolete.

How is a block validated in blockchain?

Each node in the network performs a series of tests to validate a newly solved block before propagating it to its peers. This ensures that the network only propagates valid blocks. The independent validation also ensures that honest miners have their blocks included in the blockchain and thus earn the reward.

Those miners who act dishonestly have their blocks rejected, resulting in the loss of not only the reward but also the effort expended to find a proof-of-work solution, as well as the cost of electricity without compensation.

When a node receives a new block, it validates it by comparing it to a long list of criteria that must all be met; otherwise, the block is rejected. These criteria are visible in the Bitcoin Core client in the functions CheckBlock and CheckBlockHeader, and include:

  • The block data structure is syntactically correct.
  • The block header hash is equal to or less than the target (enforces the Proof-of-Work)
  • The block timestamp is less than two hours in the future (allowing for time errors)
  • The block size is within acceptable limits.
  • The first transaction (and only the first) is a coinbase transaction.
  • Using the transaction checklist described in Independent Verification of Transactions, all transactions within the block are valid.

Bottom line

Although blocks are typically discussed in the context of cryptocurrency transactions, they may also be related to other types of digital data stored on a blockchain system.


The Genesis Block, also referred to as Block 0, is the first block in a blockchain, and it is where all subsequent blocks are added.
A block consists of transaction data, a timestamp, and block height, amongst many other things.
Blocks in Bitcoin are 1MB in size and have a 10-minute block time. Over the course of bitcoin's history, a number of increases to this limit as well as proposals to do away with it entirely have been made.
You create a block on the blockchain by starting a transaction.
Transaction hash, which includes information about recent transactions, including the sender and recipient's addresses, the amount sent, the timestamp, and the previous block's hash.
In a signed block, a user in the blockchain verifies a transaction using their private key, and the corresponding public key will help to authenticate the sender.
The distributed ledger is a decentralized database that stores data about transactions between different parties. The distributed ledger is filled with transactions in the correct order, which are then organized into blocks.

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