What Is Blockchain? A Simple Guide to Distributed Databases, Mining, and Forks

What Is Blockchain?

Blockchain is a special type of distributed database . It stores information in a way that any participant can read or write, and every node holds a full copy of the database.

Key Characteristics of Blockchain

Unlike traditional databases, blockchain has no central administrator . All nodes are equal, and the network achieves consistency by synchronizing every block across all nodes.

Because there is no manager, the system must ensure data integrity through cryptographic hashes.

Blocks

A blockchain consists of a series of blocks , each similar to a database record. Every time data is written, a new block is created.

Each block has two parts:

Block Header (Head) : records the block's characteristic values.

Block Body (Body) : contains the actual data.

The block header includes several fields, such as:

Generation time

Hash of the block body

Hash of the previous block

…

Understanding hashes is essential. A hash is a fixed‑length fingerprint computed from any input. Blockchain uses a 256‑bit SHA‑256 hash; different inputs always produce different hashes. Hash = SHA256( 区块头 ) Because the hash of a block depends only on its header, any change to the block body or previous block hash will alter the current block's hash.

Mining

To add a new block, miners must find a nonce that makes the block header's hash lower than a target value determined by the difficulty parameter. This requires exhaustive trial‑and‑error computation, and the average time to find a valid nonce is about ten minutes per block.

The difficulty is adjusted every 2016 blocks (roughly two weeks) to keep the average block time close to ten minutes. If blocks are found faster, difficulty increases; if slower, it decreases.

Difficulty Adjustment

The difficulty coefficient determines how hard it is to find a valid hash. A higher difficulty means a smaller target value, making valid hashes rarer and mining slower.

Blockchain Forks

When two blocks are created simultaneously, a fork occurs. The network resolves forks by adopting the longest chain, i.e., the branch that first reaches six additional blocks after the fork point ("six confirmations"). The branch with the most cumulative computational power becomes the canonical chain.

Conclusion

Since its launch in 2009, blockchain has operated for many years without major issues, proving its feasibility as an unmanaged distributed database. However, it has trade‑offs: low transaction throughput, high energy consumption, and limited suitable use cases. Currently, the most prominent application is cryptocurrency, exemplified by Bitcoin.