What is a blockchain?

01

A shared record book

A bank keeps the record of who owns what on its own computers. A blockchain keeps that record on thousands of computers around the world at the same time, all holding the same copy, with no single company in charge.

New entries are added in batches called blocks. Each block is tied to the one before it, which is where the name comes from: a chain of blocks.

02

Why it can't be quietly changed

Because every block is tied to the previous one, changing an old entry would mean redoing everything after it, on most of those computers at once. In practice, what is written stays written.

That is why a transaction on a blockchain is final. There is no office that can reverse it.

03

Who keeps it running

The computers that check transactions and add blocks are called validators (on Bitcoin, miners). They are paid for the work with a small fee on each transaction. That is the network fee you see on every trade and send.

04

Public by design

Anyone can look up any address and any transaction on a public website called a block explorer. An address is a string of characters, not a name, but everything it has ever held or sent is visible to everyone.

05

There are many of them

Bitcoin was the first. Ethereum added programs that run on the blockchain itself, called smart contracts. Solana is another network of that kind, and networks such as Base are built on top of Ethereum. Viru works on six: Base, Arbitrum, Optimism, Polygon and BNB Chain, and Solana.