What Is Blockchain? A Simple Guide to Its Core Concepts and Mining

After the recent Programmer's Day, blockchain's hype rose again.

Blockchain is a hot topic, widely reported as the technology that will shape the future, yet simple introductory articles are scarce.

This article aims to provide an easy‑to‑understand tutorial, covering the core concepts, mining, and why mining becomes increasingly difficult.

The Essence of Blockchain

In one sentence, a blockchain is a special distributed database.

Its main function is to store information; any data can be written to and read from the blockchain, making it a database.

Anyone can run a server, join the network as a node, and because there is no central node, each node holds a full copy of the database and synchronizes with others.

The Biggest Feature of Blockchain

Unlike traditional databases that have administrators, a blockchain is completely decentralized with no central authority.

This lack of control makes the system resistant to manipulation, but raises the question of how data integrity is ensured.

Blocks

A blockchain consists of a series of blocks, similar to records in a database.

Each block has two parts:

Block header (Head): records metadata of the current block. Block body (Body): the actual data.

The block header contains multiple pieces of metadata, including generation time, the hash of the block body, and the hash of the previous block.

Understanding the concept of a hash is essential.

A hash is a fixed‑length fingerprint computed from any content. Blockchain uses a 256‑bit SHA‑256 hash, ensuring that different inputs produce different hashes.

Example: the string 123 has the hash a8fdc205a9f19cc1c7507a60c4f01b13d11d7fd0 (hexadecimal). Only the exact string 123 yields this hash.

Inference 1: Each block’s hash is unique and can identify the block. Inference 2: Changing a block’s content changes its hash.

Hash Immutability

The hash of a block is calculated from its header:

Hash = SHA256(Block Header)

If the block body or the previous block’s hash changes, the current block’s hash also changes, making tampering evident.

Because each block links to the previous one, altering a block would require recomputing the hashes of all subsequent blocks, which is computationally infeasible without controlling the majority of the network’s hash power.

Mining

To keep the network synchronized, new blocks are added at a limited rate. Satoshi Nakamoto designed the system so that, on average, one block is generated every ten minutes.

Mining involves performing massive computations to find a hash that satisfies a difficulty target. The machines that perform this work are called miners, and their operators are miners.

Difficulty Coefficient

Not every hash qualifies; only those below a target value are accepted, making most attempts unsuccessful.

The block header includes a difficulty value that determines how hard it is to find a valid hash. For example, block 100,000 has a difficulty of 14484.16236122.

The protocol defines a target as a constant divided by the difficulty; higher difficulty yields a smaller target.

The nonce field records how many hash attempts have been made. For block 100,000, the nonce is 274148111, meaning 274 million attempts were needed.

274148111

Dynamic Adjustment of Difficulty

Because mining speed varies, the protocol adjusts the difficulty every two weeks (2016 blocks) to keep the average block time around ten minutes.

If the average time is faster, difficulty increases; if slower, it decreases, making mining progressively harder as computational power grows.

Blockchain Forks

If 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 confirmations (approximately one hour).

The branch with the majority of hash power becomes the canonical chain.

Conclusion

Blockchain, as an administrator‑free distributed database, has operated reliably for eight years since 2009.

However, it incurs costs: low throughput (transactions require at least ten minutes to be confirmed) and high energy consumption due to intensive mining.

Consequently, its practical applications are limited, with cryptocurrency being the primary use case.

References

How does blockchain really work?, by Sean Han

Bitcoin mining the hard way: the algorithms, protocols, and bytes, by Ken Shirriff