A block is a file where data (pertaining to a specific cryptocurrency network) are permanently recorded. A block records the most recent digital coin transactions that have not yet been recorded to any prior blocks.
You can imagine that a block is like a page of a huge ledger or record book which is called “blockchain”. Each time a block is fulfilled , it is like we go to the next block like by turning the page to the next empty one and so on.
So , a blockchain is a time-stamped series record of data which is immutable and is managed by a group of computers.
An open blockchain network is the very definition of a democratized system as it has no central authority.
Since blockchain is a shared ledger, the information in it is accessible and open for everyone to see.
The three pillars of the blockchain technology are: Decentralization , Transparency, Immutability.
Initially, the blockchain technology was used for Bitcoin and other cryptocurrencies , but blockchain has now found use cases in several industries like financial, health and others.
More information about blocks and mining
For the mineable coins , like Bitcoin, BitcoinZ , Digibyte etc , blocks are formed by miners.
The information of the ongoing transactions ,made with a digital coin like these, isn’t added to the blockchain straight away. Instead, it is held in a transaction pool or memory pool.
If you are a miner, your job is to gather transactions from the transaction pool in to a “candidate” block, and try to add this candidate block to the blockchain.
Each candidate block gets a block header, which is basically a bunch of metadata about the block and miners use this metadata when trying to add the block to the blockchain.
The information of this metadata includes
a) the version , describing the structure of the data inside the block so that computers are able to read the contents of each block correctly.
b) last block‘s identification number. It is the same type of number that miners are trying to get for the current candidate block.
c) the merkle root which contrains all of the transactions inside the block hashed together in order to form a single line of text. All of the fields are unique and it is considered as the most significant part of the block header.
d) the current time.
e) the target which is a value set by the digital coin network and that miners work with, in order to try and add a candidate block to the blockchain.
The target is calculated from the difficulty which is a value set by the bitcoin network to regulate how difficult it is to add a block of transactions to the blockchain.
To add a candidate block to the blockchain, the miners hash an extra arbitrary number (called “nonce” or “mining field” ) in the the data in the block header and hope that the result is below a certain target value.
If the first nonce doesn’t work (starting at 0), the miners keep incrementing it and hashing the block header. Eventually they will find a nonce that returns a block hash that is less than the target value.
Once someone has found nonce that works, the candidate block is “solved” and all of the transactions in this block are added to the blockchain.