What Is Blockchain? A Simple Guide to Blocks, Hashes, Mining, and Forks

1. Essence of Blockchain

Blockchain is a special type of distributed database. Its primary purpose is to store information that can be written to and read from any node, with every node keeping a full copy of the database and synchronizing automatically.

2. Key Feature: No Administrator

Unlike traditional databases, blockchain has no central administrator. All nodes are equal, and because there is no authority that can modify the ledger, the system is resistant to control or censorship.

3. Blocks

Each block is similar to a database record and consists of two parts:

Block Header (Head): records metadata such as timestamp, hash of the block body, and hash of the previous block. Block Body (Body): contains the actual data.

The header also stores the hash of the body and the previous block’s hash, creating a chain of blocks.

A hash is a fixed‑length fingerprint computed from any content. For example, the string 123 hashes to a8fdc205a9f19cc1c7507a60c4f01b13d11d7fd0 (hexadecimal, 256‑bit binary). Only the original content produces that exact hash.

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

4. Immutability of Hash

The hash of a block is calculated as SHA256(Block Header). Because the header includes the previous block’s hash, any alteration to a block forces the recomputation of all subsequent blocks. Without controlling more than 51% of the network’s computing power, this is practically impossible.

5. Mining

New blocks are added roughly every ten minutes. Miners compete to find a hash that satisfies a difficulty target; the first to succeed appends the block to the chain. This process is called mining, and the machines performing it are called mining rigs, operated by miners.

6. Difficulty

Only hashes lower than a target value are accepted. The target is derived by dividing a constant by the difficulty coefficient. Higher difficulty yields a smaller target, making valid hashes rarer. For example, block 100 000 has a difficulty of 14484.16236122 and a nonce of 274148111, meaning 274 million hash attempts were needed to find a valid hash.

7. Dynamic Difficulty Adjustment

To keep the average block time near ten minutes, the protocol adjusts difficulty every 2016 blocks (about two weeks). If the average time is shorter than ten minutes, difficulty increases; if longer, it decreases.

8. Forks

If two blocks are created simultaneously, a fork occurs. Nodes resolve forks by adopting the longest chain, or the chain that first reaches six confirmations (six subsequent blocks), which typically corresponds to the branch with the most cumulative computing power.

9. Summary

Blockchain operates as an administrator‑free distributed ledger that guarantees data immutability, but it incurs high latency (minimum ten‑minute confirmation) and significant energy consumption. Consequently, its practical applications are limited to scenarios where trustless, infrequent writes are essential, such as cryptocurrencies.

No universally trusted authority. Data does not require real‑time access. Mining rewards must offset operational costs.

10. References

Further reading includes articles like “How does blockchain really work?” on Medium and “Bitcoin mining the hard way” by Ken Shirriff.