What Is A Block In Blockchain?


Heard people talking about a ‘block’ in a blockchain but not sure what it is? In this blog we will simply define and explain it.

A Simple Explanation Of A Block In Blockchain

A blockchain is basically a database. A block in a blockchain is the name given to a batch of information recording some or all of a network’s most recent transactions. When the blocks are validated, they are closed or locked and a new block created. Each block is cryptographically linked to the one before it, ensuring its information cannot be altered or deleted without detection.

The Building Blocks Of Blockchain

As it sounds, a block is the building block of a blockchain. Each block is like an individual page in a ledger. They store and encrypt a lot of different information while only occupying a small amount of storage space. The blocks are joined together in sequential fashion to form a long chain.

How Blocks Make A Blockchain Secure

Blocks are identified by long strings of letters and numbers called hashes that encrypt new information as well as information from previous blocks. That is what links the blocks in the chain and makes the blockchain immutable. Immutable means no blocks or information can be altered or deleted in the blockchain. If someone tampers with a block, it causes its hash to change which unlinks it with the previous block, making all the blocks in the chain invalid and causing the chain to break.

Verifying a Block

Bitcoin blocks are verified by miners who use the proof of work consensus mechanism. Each block takes about 10 minutes to verify. To successfully conceal manipulation, every block in the chain would need its hash to be recalculated and changed which could potentially take years. Validating blocks on the Ethereum blockchain using the proof of stake mechanism is usually quicker but can still range from anywhere between 15 seconds to five minutes. Blockchain’s distributed ledger adds another layer of security. When a new block is added to the chain, it is sent to everyone in the network and has to be verified by each node before being added.

The Anatomy of a Block

Most blocks contain the following elements:

Magic number – a number with specific values that identifies which cryptocurrency network the block belongs to.

Block size – dictates the limit on the size of the block and how much information it can store.

Block header – contains information about the block, divided into six specific parts.

Transaction counter – records how many transactions have been stored in the block.

Transactions – this is the largest element of the block and lists all the transactions within it.

The Block Header

After the transaction data, the block header uses the most amount of storage. Everything else is stored in the body of the block. The block header has the following elements:

Version – the version of the cryptocurrency or software being used.

Previous block hash – a hash or encrypted number of the previous block’s header that forever ties it to that block, to make altering or deleting data impossible without detection.

Hash Merkle root – a hash of transactions in the Merkle tree of the block. (A hash tree or Merkle tree encodes blockchain data more securely).

Timestamp – the time in seconds since 1/1/1970, T00:00 UTC.

Bits – the difficulty rating or “target difficulty” of the block which determines how hard the target hash will be to find for miners or validators.

Nonce – a 32-bit number that a miner or validator must alter to solve the computational puzzle for the block and close it.

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