A blockchain is exactly what it sounds like it is: a chain consisting of blocks of information. These blocks are containers holding a record transactions on the blockchain. In the case of Bitcoin, the transactions are primarily transfers of bitcoins. On some blockchains, they can also contain a variety of other information, even code of computer programs.
What are the blocks in blockchain?

Once transactions are added to the block, they cannot be reversed. And when a block is added to the chain, it cannot be changed. All information held in blocks is going to stay there as long as the blockchain exists. Blocks are added on top of one another in a linear way. One by one, they form a chain holding the entire history of transactions on the network.

The exact structure of blocks can differ from blockchain to blockchain. This article will focus on explaining the structure of a Bitcoin block. After all, that is the basis on which most other blockchains were modelled.


  • Blocks are the basic containers of information in a blockchain.
  • They contain transaction data.
  • Once added to the blockchain, a block cannot be changed.
  • Blocks are secured with cryptographic methods.

The parts of a block

The body of a block contains transaction records. Storing these records safely is one of the priorities of the blockchain. But to be able to function in a blockchain, a block also needs a few other elements. But before we find out what they are, let’s first see how data is stored in blocks.

Cryptocurrencies earned their name because they rely heavily on cryptography. In the case of blocks, the cryptographic principle used is called the hash function. A string of symbols, called a hash, is determined through a hashing algorithm. Bitcoin uses SHA-256, but not all cryptocurrencies use the same algorithm. This algorithm takes all the data in a block and turns it into a unique string of symbols that serve as the block’s ID.

The hash of the block (the block header) is formed from the six elements that make up a block:

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

All except the last of these elements are known in advance before a block is added to the chain. The nonce, however, remains a mystery. The purpose of crypto mining is to figure out the nonce. The miner who first finds the nonce that satisfies the current difficulty requirement adds the block to the chain, sealing it into the history of transactions. See our article on mining to find more about how this is done.

Understand what you trade

There are many misconceptions about cryptocurrencies, and understandably people may be wary of using something that is all-too-often over-hyped, while under-explained. Wrapping your head around blockchains and cryptocurrencies does not require specialist knowledge and programming experience, and the wise user will get to know this ground-breaking world as best they can, before deciding whether, and how, to invest in it. We are here to help.

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