What Is Blockchain?
Imagine a giant ledger where every transaction gets recorded, but with one particularity: no one can erase or modify what's already written, and thousands of people hold an identical copy of this ledger.
That, in essence, is a blockchain.
The ledger analogy
At a traditional bank:
- The bank holds a single copy of the transaction record
- You trust that the bank won't alter your data
- If the bank disappears, you lose access to your money
On a blockchain:
- Thousands of computers (called nodes) hold a copy of the record
- Transactions are verified mathematically, not by trust
- There's no single point of failure
Why is it called "blockchain"?
Transactions are grouped into blocks. Each block is linked to the previous one through cryptography, forming a chain of blocks (block + chain).
If someone tries to modify Block 2, the cryptographic link to Block 3 breaks. Every node on the network would immediately detect that something is wrong.
Distributed vs. Decentralized
Block Explorers: watching the transactions
One of blockchain's most powerful features is its transparency. Anyone can see any transaction that has ever happened.
Block explorers are websites that let you explore the blockchain:
| Blockchain | Block Explorer |
|---|---|
| Bitcoin | mempool.space |
| Ethereum | etherscan.io |
| Solana | solscan.io |
What can you see in a block explorer?
- Transactions: Who sent how much to whom, and when
- Addresses: A wallet's balance and its entire history
- Blocks: All the transactions included in each block
- Contracts: Smart contract code (on blockchains like Ethereum)
Try it yourself
Look up this address on Solana: D8Lu3ntZPAjtyzSgZvF95G48oaEhUxJCfArdrGy2KD23. You'll see its balance and its whole transaction history. Anyone can see this — it's public.
Gas: the cost of transactions
Every transaction costs a fee, called gas, which goes to whoever processes and verifies the network. It's always paid in that blockchain's native currency: ETH on Ethereum, SOL on Solana, even when what you're moving is USDC.
How much it costs depends on the blockchain: some prioritise security (Bitcoin) and others speed and low cost (Solana), and that shows up in both the per- transaction cost and the confirmation time.
→ Gas: why every move costs something
Different blockchains
There's no single blockchain. There are many, each with very different characteristics:
| Blockchain | Native currency | What it's used for | Cost per transaction | Confirmation |
|---|---|---|---|---|
| Bitcoin | BTC | Store of value, large payments | dollars, rises with congestion | 10 – 60 min |
| Ethereum | ETH | Smart contracts, DeFi | dollars; tens during peaks | ~15 sec |
| Arbitrum | ETH | Cheaper Ethereum | cents | 1 – 2 sec |
| Base | ETH | Cheaper Ethereum | cents | 1 – 2 sec |
| Polygon | POL | Payments, stablecoins | cents | ~2 sec |
| Solana | SOL | High speed, apps, memecoins | fractions of a cent | ~1 sec |
| Hyperliquid | HYPE | Derivatives trading | fractions of a cent | under 1 sec |
Orders of magnitude, not prices
This table deliberately avoids exact figures: costs change with each network's congestion, and any concrete number goes stale within weeks.
The practical rule: if you're moving less than $50, don't use Ethereum mainnet. Use an L2 (Arbitrum, Base, Polygon) or Solana.
Watch out for "TPS"
You'll see the figure transactions per second a lot in comparisons between blockchains. It's almost always the theoretical lab maximum, not what the network does in practice, and it's a number projects use as a sales pitch. For what you're going to do, what matters is what's in the table: how much it costs and how long it takes.
Summary
- A blockchain is a distributed, immutable record of transactions
- Data is grouped into blocks linked cryptographically
- Every transaction requires paying gas in the native currency
- Costs and speeds vary a lot between blockchains
- You can verify any transaction using a block explorer
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