Topic
What is blockchain?
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- Quick fact 1
A blockchain is a shared record copied across many computers.
- Quick fact 2
New entries are added in groups called blocks, and each block links to the one before it.
- Quick fact 3
Changing an old entry would mean redoing the work on most of the network, which makes it very hard to cheat.
The short lesson
Think of a notebook that thousands of people keep at the same time. Every time someone writes a new line, everyone adds the same line to their copy. If one person tries to erase a page in their notebook, it won't match everyone else's, so the change gets rejected. That's the basic idea of a blockchain.
On a blockchain, entries are grouped into blocks. Each block carries a code made from the block before it. If anyone changes an old block, its code changes, and every block after it breaks. To fake the record, a cheater would need to control most of the network at once. That's why blockchains are very hard to change.
Blockchains are best known for cryptocurrency, like Bitcoin. The record shows which wallet sent value to which wallet. But the same idea can track other things, too, like who owns a digital item.
Three things beginners often mix up:
- The blockchain is the record. It's the shared notebook.
- A coin or token is what moves on it. Bitcoin is a coin on the Bitcoin blockchain.
- Apps and exchanges are built on top. They can be hacked or fail even when the blockchain itself keeps working.
A blockchain makes the record hard to change. It doesn't make every project on it honest.
Related terms
Go deeper in Lesson 4: The shared list everyone can check
Common questions
Is blockchain the same as Bitcoin?
No. Bitcoin uses a blockchain, but a blockchain is the record-keeping method. Many other networks use their own blockchains.
Can a blockchain be hacked?
Large blockchains are very hard to change. Most losses happen around them, through hacked apps, exchanges, or stolen keys.
Who runs a blockchain?
On public blockchains, the record is run by many computers following shared rules. Private blockchains are run by one company or group.
Why do people say blockchain is secure?
Each block is linked to the one before it, and many computers hold copies. Changing the past would mean changing most of those copies at once.