How a Block Works in a Blockchain
Today we’ll talk about how a block in a blockchain is structured. This is the foundation of the technology behind cryptocurrencies and many modern digital solutions. We’ll break down what a block is, how it works, and why blockchain is considered a reliable data storage system.
1. What is a Blockchain?
A blockchain is a sequential chain of blocks, where each block contains information about transactions. You can imagine it as a digital record book: each new page (block) is added only after the previous one is written and verified.
Blocks are linked one after another — each new block contains a reference to the previous one.
Changing data is practically impossible — if someone tries to alter the information in one block, the entire chain becomes invalid.
The data is publicly accessible — information in the blockchain is transparent and can be verified.
You can read more about blockchain in the previous article.
2. How is a Block Structured?
A block in a blockchain can be thought of as a digital container that holds data. It consists of two key parts:
Header — contains important technical information:
Timestamp — when the block was created.
Hash of the block — a unique code generated from the block's data.
Hash of the previous block — a reference to the previous block, which ensures the continuity of the chain.
List of transactions — the main content of the block, storing all recorded operations. These transactions may include:
Financial transfers (such as cryptocurrency payments).
Smart contract execution data.
Other types of information, such as property records or healthcare data.
Thanks to this structure, blocks are securely linked into a chain. This makes it possible to trace the entire history of data from the very first block and prevents tampering. If someone attempts to change the data in a single block, it changes the hashes of all subsequent blocks, and the system immediately detects the modification.
3. What is a Hash?
A hash is a unique digital code generated using a special algorithm called a hash function. Think of it like a fingerprint for data: every unique dataset produces its own distinct hash.
Here’s how it works:
If you take a text like “Hello, world!” and run it through a hash function, you get a string of characters (the hash).
If you change even one character in the text, the hash will change completely.
Hashes are one-way — you can’t reverse them back into the original data.
Hashes are important in blockchain for several reasons:
Tamper protection — if someone changes the data in a block, its hash changes, making the tampering immediately obvious.
Efficient verification — instead of comparing full data sets, systems can compare just the hashes.
Chaining blocks — each block contains the hash of the previous block, creating a strong and secure chain.
Hashing is what makes blockchains secure and immutable, ensuring the integrity of stored information.
4. How Are New Blocks Added?
Think of a blockchain as a long chain of locks, where each new lock (block) is securely attached to the previous one. If someone tries to tamper with one lock, the whole chain becomes invalid.
Here’s how a new block is added:
Data gathering — transaction data is collected for the new block.
Hash generation — the block’s data is transformed into a unique hash.
Linking — the new block includes the hash of the previous block, creating a secure connection.
Validation and addition — once verified, the block is officially added to the chain.
If someone tries to alter a block (for example, block #233), its hash will change. The next block (block #234) won’t recognize the new hash, breaking the chain. This is why any tampering with blockchain data is quickly detected and rejected by the network.
5. Who Verifies the Blocks?
Before a new block is added to the chain, it must be validated. This is done by miners — special network participants who ensure the proper functioning of the blockchain. You can think of miners as inspectors making sure everything is accurate and fair.
Miners perform three key tasks:
Hash calculation — they search for a correct value that will allow the block to be added.
Block confirmation — once the correct value is found, the block is validated and added to the blockchain.
Data integrity check — if someone tries to modify a past block, the system will reject it.
To add a block, the miner must solve a complex mathematical puzzle. In Bitcoin, for example, this puzzle is designed to take about 10 minutes to solve. This timing ensures that blocks are added at a predictable pace.
Miner Rewards
The first miner to solve the puzzle gets to add the block to the chain and receives a reward — newly minted coins (like Bitcoin) and transaction fees.
This reward system motivates miners to keep the network secure and functioning.
6. How Do Miners Add Blocks?
Mining is like a game of “guess the number.” Miners compete to find a number (called a nonce) that, when combined with the block’s data, produces a valid hash.
Here’s the step-by-step mining process:
Transaction collection — the block is filled with new transactions.
Nonce selection — the miner repeatedly changes a random number (nonce).
Hash calculation — the block’s data and the nonce are hashed together.
Hash verification — the resulting hash must meet strict criteria (such as starting with a specific number of zeros).
Trial and error — if the hash is invalid, the miner tries a new nonce. This may happen millions of times.
Success and reward — the first miner to find a valid hash gets to add the block and claim the reward.
Why is mining difficult?
It requires huge computing power due to the complexity of finding a valid hash.
Miners use powerful computers and specialized devices (ASICs) to perform millions of calculations per second.
The faster the hardware, the better the miner’s chances of winning.
Mining Rewards The successful miner receives:
Newly generated coins.
Transaction fees included in the block.
Mining is a key part of how blockchain networks function and stay secure.
Conclusion
Blockchain is a secure system that stores data in a series of linked blocks. Each block is connected to the previous one, and altering the data breaks the chain. Miners verify and add new blocks by solving complex puzzles, helping maintain trust and transparency in the system.
This technology is used not only in cryptocurrencies but also in finance, logistics, healthcare, and many other areas where reliable and transparent data handling is essential.
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