If you’ve ever looked at a blockchain explorer and wondered what on earth you were looking at, you’re not alone.
You might see hundreds of transactions, long strings of letters and numbers, blocks, timestamps and something called a transaction hash. It can look complicated enough to make you close the page immediately.
But the basic idea behind a blockchain is surprisingly simple.
A blockchain is a shared digital record that is maintained by a network of computers rather than one central authority.
That’s the starting point. Everything else builds on it.
Let’s forget crypto for a moment
Imagine that ten people in a room keep copies of the same notebook.
Whenever someone makes a transaction, everyone updates their copy.
If Chinedu sends 2 units to Ada, the group records it.
If Ada tries to send those same 2 units to someone else before actually receiving them, the group can check the previous records and reject the transaction.
Nobody has to trust one person’s notebook because everyone has a copy.
A real blockchain is obviously much more sophisticated than this example, but the underlying idea is similar.
Instead of one organization maintaining the database, multiple computers on a network participate in maintaining and verifying it.
That’s where the word distributed comes in.
What exactly is stored on a blockchain?
The answer depends on the blockchain.
At a basic level, blockchains record transactions and other pieces of data required by their particular protocol.
On Bitcoin, for example, transactions record transfers of Bitcoin between addresses.
On Ethereum, the blockchain records transactions and changes to the state of the network. Ethereum can also execute smart contracts, which are programs stored and run on the blockchain. (ethereum.org)
So a blockchain isn’t necessarily just a giant list of payments.
It can also serve as the foundation for applications.
That’s one of the reasons blockchain technology became much bigger than Bitcoin.
Why is it called a blockchain?
This part is actually pretty straightforward.
Transactions are grouped together into blocks.
Those blocks are then connected to one another, forming a chain.
Hence:
Block + Chain = Blockchain
A block generally contains information about the transactions it includes, along with other information needed by the network.
One particularly important piece of information is a cryptographic reference to the previous block.
That connection is one of the reasons changing old blockchain records is so difficult.
If someone attempted to alter information in an earlier block, the cryptographic relationships between the blocks would no longer line up.
They would effectively be trying to rewrite part of the chain and convince the rest of the network to accept their version.
That’s not an easy thing to accomplish on a large, properly functioning blockchain.
What is a block?
Think of a block as a container.
Transactions are waiting to be included in the blockchain.
The network processes them according to its rules, and a group of transactions is eventually included in a block.
Once that block is accepted by the network, it becomes part of the blockchain.
More blocks follow it.
You can therefore imagine the blockchain roughly like this:
Block 1 → Block 2 → Block 3 → Block 4 → Block 5
Block 5 points back to Block 4.
Block 4 points back to Block 3.
And so on.
This creates a historical record of the chain’s activity.
Who keeps the blockchain?
This is where blockchain technology becomes more interesting.
The blockchain is maintained by computers participating in the network. These computers are commonly referred to as nodes.
A node can maintain and verify blockchain data according to the rules of the particular network.
Bitcoin’s network, for example, is made up of computers communicating with one another using the Bitcoin protocol. Bitcoin’s documentation describes the network as a peer-to-peer system where participants can verify transactions and maintain the shared ledger without a central authority. (bitcoin.org)
You can think of nodes as the people in our imaginary room who each keep a copy of the notebook.
The difference is that we’re now talking about computers spread across the world.
What happens when you send cryptocurrency?
Let’s say you want to send some Bitcoin to a friend.
You open your wallet and enter their Bitcoin address.
Your wallet creates a transaction and uses your private key to authorize it.
The transaction is then broadcast to the Bitcoin network.
Nodes receive the transaction and check whether it follows the network’s rules.
For example, they can verify whether the transaction is properly authorized and whether the inputs being spent are valid.
If the transaction passes the necessary checks, it can eventually be included in a block.
Once that block is accepted by the network, the transaction becomes part of the blockchain.
Your friend can then see that the transaction has been recorded and, depending on the network and number of confirmations, treat the funds as available.
There’s quite a lot happening behind that simple “Send” button.
What are nodes?
A node is essentially a computer participating in a blockchain network.
But not every node necessarily performs exactly the same job.
Some nodes maintain copies of blockchain data and verify that transactions and blocks follow the rules.
Other specialized participants may be responsible for proposing or producing blocks, depending on the blockchain’s consensus mechanism.
This distinction matters because people sometimes imagine that “the blockchain” is one giant computer.
It isn’t.
It’s a network of computers communicating and agreeing on the state of a shared system.
How does the network agree on what’s valid?
Now we reach one of the most important concepts in blockchain:
consensus.
Imagine thousands of computers are maintaining the same ledger.
What happens if some of them disagree?
Which transaction should be accepted?
Which block comes next?
Which version of the blockchain should everyone follow?
A blockchain needs a way for participants to reach agreement about the state of the network.
That’s what consensus mechanisms are designed to do.
Different blockchains use different approaches.
Bitcoin uses Proof of Work.
Ethereum uses Proof of Stake. Ethereum moved from Proof of Work to Proof of Stake in September 2022 in an upgrade commonly known as The Merge. (ethereum.org)
The two systems work very differently.
How does Bitcoin’s Proof of Work work?
Bitcoin’s approach involves miners.
Miners use computing power to compete in solving a computational puzzle associated with creating a new block.
The process requires substantial computational work.
When a miner successfully produces a valid block, the network can verify the result relatively easily.
This is where the term mining comes from.
It isn’t because computers are literally digging Bitcoin out of the ground.
Mining is the process through which participants use computational work to help secure the Bitcoin network and add new blocks.
Bitcoin’s protocol also rewards successful miners according to its rules, including newly issued Bitcoin and transaction fees. (bitcoin.org)
What about Proof of Stake?
Proof of Stake takes a different approach.
Instead of relying on miners competing with computing power, networks using Proof of Stake use validators who commit cryptocurrency to participate in the network.
Ethereum’s documentation explains that validators stake ETH and can be selected to propose and attest to blocks. (ethereum.org)
There are penalties for validators who violate the network’s rules.
The important thing to remember is that Proof of Work and Proof of Stake are different methods of achieving consensus.
Neither should simply be treated as a different name for the same process.
Why can’t someone just change a blockchain?
This is probably one of the first questions that comes to mind.
If blockchain data is stored digitally, what’s stopping someone from opening the database and changing a transaction?
Several things.
First, blockchains use cryptographic techniques to link and verify data.
Second, copies of the blockchain are maintained across a distributed network.
Third, participants follow a set of consensus and validation rules.
So changing a record isn’t as simple as editing a row in a normal database.
An attacker would have to overcome the mechanisms used by that particular blockchain to accept an altered history.
Exactly how difficult that is depends on the blockchain and its security model.
This is also why saying “blockchain data can never be changed” is a little too simplistic.
A better way to think about it is:
Blockchain systems are designed to make unauthorized changes extremely difficult, especially once data has been deeply confirmed by a secure network.
What is a transaction hash?
You’ve probably seen something that looks like this when exploring crypto transactions:
0x7f3...a92
It might look like complete nonsense at first.
That’s usually a hash or part of a transaction identifier.
A cryptographic hash takes data and produces a fixed-length output.
Even a small change to the original information can produce a completely different hash.
This makes hashes useful for identifying data and detecting changes.
For example, if a blockchain block contains a particular set of transactions, cryptographic information associated with that block helps connect it to the chain.
You don’t need to understand the mathematics behind cryptographic hashing to start using crypto.
But understanding the basic purpose helps:
Hashes help blockchains identify, link and verify information.
Is blockchain the same thing as Bitcoin?
No.
This is another distinction beginners should learn early.
Bitcoin is a cryptocurrency and a blockchain network.
Blockchain is the underlying type of technology used by Bitcoin and many other networks.
A simple comparison would be the relationship between email and the internet.
Email uses the internet, but the internet isn’t email.
Similarly, Bitcoin uses blockchain technology, but blockchain technology isn’t Bitcoin.
Ethereum, Solana and many other blockchain networks have their own designs, rules and purposes.
Why did Ethereum change what blockchains could do?
Bitcoin demonstrated that blockchain technology could support decentralized digital money.
Ethereum took the concept further.
Instead of designing a blockchain primarily around transferring one currency, Ethereum was designed to support programmable smart contracts.
A smart contract is a program deployed on a blockchain that executes according to its programmed rules. Ethereum describes smart contracts as programs that run on the Ethereum blockchain. (ethereum.org)
That opened the door to things such as decentralized applications, decentralized finance and tokenized assets.
We’ll get into Ethereum properly in another LearnTheCrypt guide.
For now, just remember that a blockchain can be more than a payment ledger.
Why does blockchain matter?
Blockchain technology isn’t useful simply because it is new or because cryptocurrency prices go up.
Its more interesting idea is that it provides a way for people and computers that don’t necessarily trust one another to coordinate around a shared record.
That’s a powerful concept.
It can be used for digital money.
It can support programmable applications.
It can create systems where ownership and transactions can be publicly verified.
But blockchain isn’t automatically the best solution for every problem.
A normal centralized database can often be faster, cheaper and much simpler when there is no reason to decentralize the system.
Understanding that distinction is important.
The simplest way to remember how blockchain works
If you’ve forgotten everything else in this article, remember this:
A blockchain is a distributed digital ledger.
Transactions are recorded.
Transactions are grouped into blocks.
Blocks are linked together.
Network participants verify the data.
A consensus mechanism helps the network agree on which blocks and transactions are valid.
And cryptography helps protect the integrity of the system.
That’s the foundation.
Once you understand that, terms like Bitcoin, Ethereum, wallets, mining, validators, smart contracts and Web3 stop sounding like completely unrelated pieces of technology.
They start fitting together.
And that’s exactly where we go next.
In the next LearnTheCrypt guide, we’ll look at Bitcoin itself—why it was created, how transactions work, where new Bitcoin comes from, what mining actually does, and why there will only ever be 21 million Bitcoin.
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