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

1. The Essence of Blockchain

Blockchain is essentially a special kind of distributed database. Its primary role is to store information, allowing any data to be written to or read from the chain, making it a database.

Anyone can run a server, join the network as a node, and because there is no central node, every node holds a full copy of the database. All nodes synchronize, ensuring consistency.

2. The Biggest Feature of Blockchain

While distributed databases are not new, blockchain introduces a revolutionary characteristic: it has no administrator and is completely decentralized.

Because there is no central authority, the system cannot be controlled or censored, which also raises the question of how trust is maintained without a manager.

3. Blocks

A blockchain consists of a series of blocks, similar to records in a database. Each block has two parts: a block header (metadata) and a block body (actual data).

Block header contains items such as generation time, the hash of the block body, the hash of the previous block, and other metadata.

Generation time

Hash of the block body

Hash of the previous block

…

The hash is a fixed‑length fingerprint of any content; for example, the string "123" hashes to a8fdc205a9f19cc1c7507a60c4f01b13d11d7fd0 (hexadecimal, 256‑bit binary).

Inference 1: Each block’s hash is unique and can identify the block.

Inference 2: Changing a block’s content changes its hash.

4. Immutability of the Hash

Hash = SHA256(Block Header)

The hash is calculated solely from the block header, using the SHA‑256 algorithm. If either the block body’s hash or the previous block’s hash changes, the current block’s hash also changes, breaking the chain unless all subsequent blocks are recomputed—a practically impossible task without controlling >51% of the network’s computing power.

5. Mining

To keep the network synchronized, new blocks are added slowly—approximately one every ten minutes. This deliberate difficulty, designed by Bitcoin’s creator Satoshi Nakamoto, ensures that the whole network must perform massive computation to find a valid hash, a process called mining.

6. Difficulty Factor

The block header also contains a difficulty value that determines how hard it is to find a hash below a target threshold. Higher difficulty means a smaller target, making valid hashes extremely rare.

The header stores a nonce counting how many hash attempts have been made; for block #100000 the nonce was 274148111, meaning 274 million attempts were needed.

7. Dynamic Adjustment of Difficulty

To keep the average block time close to ten minutes, the difficulty is adjusted every two weeks (2016 blocks). If the average time is faster, difficulty rises; if slower, it falls, ensuring a steady block production rate.

8. Blockchain Forks

If two blocks are created at the same time, the chain temporarily forks. The rule is that the longest chain (the one that first reaches six confirmations after the fork) is considered the valid one, reflecting the branch with the most computing power.

9. Summary

Since its launch in 2009, blockchain—a decentralized distributed database—has operated for over eight years without major issues, proving its feasibility. However, it incurs costs: low transaction throughput (minimum ten‑minute latency) and high energy consumption due to mining.

Consequently, blockchain’s practical applications are limited to scenarios where participants do not trust a central authority, data does not need real‑time use, and mining rewards offset costs; otherwise, traditional databases are preferable.

10. References

How does blockchain really work?, by Sean Han – https://medium.freecodecamp.org/how-does-blockchain-really-work-i-built-an-app-to-show-you-6b70cd4caf7d

Bitcoin mining the hard way: the algorithms, protocols, and bytes, by Ken Shirriff – http://www.righto.com/2014/02/bitcoin-mining-hard-way-algorithms.html