When discussing bitcoin mining, the term “blocks” often comes up in conversation. In today’s article, we’ll take a moment to explain what a bitcoin block actually is.
What is a block?
A block is where transaction data files are permanently stored. Blocks are structured in a linear structure over time, which is known as a blockchain.
New transactions are continually integrated into new blocks, which are placed at the end of the chain. The more blocks that are added to the blockchain, the harder it is to alter or remove older ones, making Bitcoin transactions irreversible and immutable. A Bitcoin block typically has on average over 500 transactions. For example, Bitcoin Cash (a hard fork of Bitcoin) has a block size of up to 8 MB, which allows more transactions to be processed per second.
Each block consists of a record of recent transactions, a reference to its previous block, and the solution to a complex algorithm that is unique to each block. New blocks cannot be added to the network without the correct solution. The act of “mining” involves finding the answer that will solve the current block.
Mathematical puzzles have a high degree of difficulty, but once the correct solution is identified, the rest of the network can easily confirm the validity of the solution. There are multiple solutions that can be considered valid for each block, but only one of them needs to be found for the block to be added to the chain.
Since a reward of newly minted bitcoins is given upon solving each block, each block records which bitcoin addresses or scripts should receive the rewards. This record is called a generation transaction or coinbase transaction; it will always be the first transaction to appear in the block. Bitcoins were initially generated 50 per block completion, and this number continues to increase every 210,000 blocks (about four years). This means that at block 210,000, the block creation rate has been reduced to 25 BTC, and 12.5 BTC will be produced at block 420,000, leading to 0 satoshis at the completion of block 6,930,000.
Bitcoin transactions are sent to the network and all of the sender's peers who want to solve blocks collect the transaction records and add them to the block they are trying to solve. Miners are motivated to put transactions into their blocks due to afferent transaction fees.
Block difficulty is automatically adjusted by the network so that on average a target of 6 blocks is solved every hour. Every 2016 blocks (solved in approximately 2 weeks), all Bitcoin clients compare the number generated to adjust the target by the percentage that has changed. A consensus is reached by the network and the block difficulty is automatically increased or decreased.
If two different valid solutions are found simultaneously for the same block, the network will accept the 'longer' blockchain as valid. The 'length' represents the chain with the most combined difficulty, not the one with the most blocks. This is done to avoid forking the chain and generating multiple low-difficulty blocks.
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Block structure
A block consists of a header and a long array of transactions.
Block header
The header consists of block metadata. In a header, there are three types of metadata:
THE hash of previous block. In a blockchain, each block inherits from the previous block because the hash of the previous block is needed to generate the hash of the new block. Thus, every block N receives the hash of block N-1.
Mining competition . In order for a block to be added to a blockchain, it needs to receive a valid hash. This consists of a timestamp and a difficulty.
A root of the merkle tree. This data structure summarizes all transactions in a block.
Block identifiers
To identify the block, you need to have a hash, considered a digital signature. This is generated by hashing the block header twice using the implementation of a SHA256 algorithm.
As we mentioned above, each block uses the hash of the previous block to create its own hash. The block hash represents a unique identifier. This means that no two blocks have the same hash.
Another way to identify a specific block is by its block height. This represents the position of the blocks in the blockchain. Unlike a hash, a block height is not unique. More blocks may compete for the same position if there is a fork in the blockchain.
Merkle Trees
A merkle tree or binary hash tree is a structure in which all transactions in a block are recorded.
A Merkle tree consists of a function that recursively hashes pairs of nodes (in our case, transactions), until only one hash remains, called the root or Merkle root. In the Bitcoin world, the cryptographic hashing algorithm used for hashing is SHA256, and this is applied twice each time.
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Conclusion
We hope our article has answered some of your questions about Bitcoin blocks. Of course, there is still a lot to explain about this system, but now you have a broader idea of what is happening in the mining process and what a block actually represents in the blockchain structure.