A blockchain is a digital record that stores transaction information in linked blocks, with each block connected to the one before it

Think of a blockchain as a chain of digital containers, each holding a list of transactions. When a new transaction happens—say, someone sends Bitcoin to someone else—that transaction gets bundled with others into a "block." Once a block fills up, it gets sealed with a unique code (called a hash) and linked to the previous block. This creates an unbreakable chain going back to the very first block ever made.

The key difference from a regular database is that no single person or company controls it. Instead, thousands of computers (called nodes) each keep a complete copy of the entire blockchain. When someone tries to add a new block, the network checks it against all those copies to make sure it's legitimate. If the copies don't match, the block gets rejected. This makes it extremely hard for anyone to cheat or change past transactions.

Key Takeaways

  • A blockchain stores transactions in blocks that are linked together in chronological order, with each block containing a unique code that connects it to the previous one.
  • Thousands of computers maintain identical copies of the blockchain, so no single entity can control or alter the record without detection.
  • Before a new block is added, the network must verify the transactions inside it using a process like proof of work or proof of stake.
  • Once a block is added to the chain, changing it would require redoing all the blocks that came after it, which becomes mathematically impossible as the chain grows.
  • Different cryptocurrencies use different blockchains—Bitcoin has its own, Ethereum has its own, and they don't share transaction records.

How blocks get added to the chain

When you send cryptocurrency, your transaction enters a waiting area called the mempool. Miners or validators (depending on the network) collect pending transactions and bundle them into a new block. Before that block can join the chain, the network has to verify it's real—that you actually own the coins you're sending and that you haven't already spent them elsewhere.

Bitcoin uses a process called proof of work, where miners solve complex math puzzles to earn the right to add the next block. This takes computational power and electricity, which is why Bitcoin mining is resource-intensive. Ethereum switched to proof of stake, where validators are chosen based on how much cryptocurrency they've locked up as collateral. Both methods make it expensive or risky to cheat, because the cost of trying to fake a transaction exceeds any gain.

Once a block is verified and added, it gets a timestamp and a unique fingerprint (hash). The next block includes that fingerprint in its own code, creating the "chain." Change even one character in an old block, and its hash changes, which breaks the link to every block after it. The network would immediately spot the tampering.

Why the chain can't be reversed or faked

Imagine someone wanted to go back and change a transaction from six months ago. They would have to redo that block, which changes its hash. Then they'd have to redo every single block that came after it, because each one depends on the hash of the one before. Meanwhile, the rest of the network keeps adding new blocks to the real chain. The attacker would have to work faster than the entire network combined—and do it on thousands of computers simultaneously, since each node has a copy.

This is why older transactions are considered more secure. A transaction from yesterday is easier to attack than one from a year ago, simply because there are more blocks stacked on top of it. Most exchanges and services wait for a certain number of new blocks to be added (usually 6 to 12) before treating a transaction as final and irreversible.

Different cryptocurrencies have different blockchains

Bitcoin runs on the Bitcoin blockchain. Ethereum runs on the Ethereum blockchain. They are separate networks that don't talk to each other. If you send Bitcoin, it only moves along the Bitcoin blockchain. If you send Ethereum, it only moves along the Ethereum blockchain. Each blockchain has its own set of nodes, its own transaction history, and its own rules for how blocks are created and verified.

This is why you can't send Bitcoin directly to an Ethereum address—they're on different systems. Some newer projects called "bridges" try to connect blockchains so you can move value between them, but these bridges are still experimental and carry their own risks.

What information gets stored in each block

Each block typically contains a list of transactions (the "payload"), a timestamp showing when the block was created, the hash of the previous block (the link in the chain), and a nonce—a number used only once that helps miners or validators prove they did the work. The exact contents vary by cryptocurrency, but the core idea is the same: record who sent what to whom, and when.

The blockchain itself is public. Anyone can download it and see every transaction ever made on that network. You can't see names attached to addresses (Bitcoin addresses are long strings of characters), but you can see the flow of money. This transparency is intentional—it's what makes the system trustworthy. If the ledger were hidden, you'd have to trust someone else to keep it honestly.

Mining and validation: who maintains the blockchain

On Bitcoin, miners compete to solve puzzles and earn the right to add blocks. The winner gets newly created Bitcoin plus transaction fees. This incentive keeps miners running expensive equipment and securing the network. On Ethereum and similar networks, validators stake their own cryptocurrency as collateral. If they try to cheat, they lose their stake. If they behave honestly, they earn rewards.

Both systems are designed so that honest behavior is more profitable than dishonest behavior. A miner who spends electricity trying to fake a transaction would lose money. A validator who lies would lose their collateral. This economic design is what makes blockchains work without a central authority.

Frequently Asked Questions

Can the government shut down a blockchain?

No single government can shut down a decentralized blockchain because it runs on thousands of computers in different countries. A government could ban its citizens from using it or make it illegal to trade, but the blockchain itself would keep running. Bitcoin has survived for over 15 years despite regulatory pressure in many countries.

Is blockchain the same thing as cryptocurrency?

No. Blockchain is the technology—the record-keeping system. Cryptocurrency is what gets recorded and transferred. Bitcoin is a cryptocurrency that uses blockchain technology. You could use blockchain for other things, like tracking supply chains or storing medical records, without any cryptocurrency involved.

How long does it take to add a new block?

Bitcoin adds a new block roughly every 10 minutes on average. Ethereum adds one roughly every 12 seconds. The network adjusts the difficulty of the puzzle or the number of validators to keep the timing consistent, even as more miners or validators join.

What happens if two blocks are created at the same time?

Occasionally the network splits temporarily into two versions, each following a different block. The network resolves this by following whichever chain becomes longer first. Miners and validators then abandon the shorter chain and sync to the longer one. This is called a "fork" and usually resolves within minutes.

Can I lose my cryptocurrency if the blockchain fails?

A blockchain cannot fail in the way a company can. As long as even one node keeps running, the blockchain exists. Your coins are safe as long as you control your private key—the password that proves you own them. Losing your private key is the real risk, not the blockchain itself.