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How Blockchain Is Formed and What a Block Contains?

General Structure of Blockchain​

Blockchain is a sequential chain of blocks where each block contains a set of data and is linked to the previous block using cryptographic mechanisms. This structure ensures data integrity and consistency throughout the system.

New blocks are added strictly sequentially, allowing for an unambiguous ordering of all records in the ledger.

What Is a Block​

A block is the basic structural unit of a blockchain. It serves as a container for storing data and includes both user information and service elements necessary for network operation.

Each block is formed according to specific rules that depend on the particular blockchain system.

Main Elements of a Block​

A typical blockchain block includes the following components:

  • Data (payload)
    Usually transactions or other records that need to be recorded in the ledger.

  • Hash of the previous block
    A cryptographic value that uniquely identifies the previous block in the chain.

  • Block's own hash
    The result of applying a hash function to the entire block content.

  • Service information
    Includes timestamp, consensus parameters, and other technical data.

Linking blocks through hashes creates a chain where each block depends on the previous one.

Block Linking and the Role of Hash Functions​

A hash function transforms input data of arbitrary size into a fixed-length string. Even a minor change in the original data results in a completely different hash output.

In blockchain, this property is used to ensure integrity: if data in one block is changed, its hash changes, causing a mismatch with the next block and breaking the entire chain.

Merkle Tree​

For efficient storage and verification of a large number of transactions in a block, a data structure known as a Merkle tree is used.

Transactions are paired and hashed, then the resulting hashes are paired and hashed again until a single root hash is obtained. This root hash is included in the block and allows quick verification of all transaction integrity without needing to store them in full. When the number of transactions is odd, the unpaired transaction is combined with itself.

Block Size Limitations and Throughput​

In some blockchain systems, block size is limited. This limitation affects the number of transactions that can be included in a block and, consequently, the network's throughput.

For example, in early implementations of the Bitcoin blockchain, block size was limited, resulting in a limited number of transactions per second and stimulating the development of second-layer solutions.

Brief Summary​

Blockchain is formed as a sequential chain of blocks where:

  • each block contains data and a reference to the previous block,
  • hashing ensures integrity and protection against tampering,
  • additional data structures such as Merkle trees improve network efficiency.

Understanding block structure and block linking principles is essential for further study of consensus mechanisms and blockchain system security.