The Blockchain

A blockchain is a shared digital ledger that records transactions or data in a way that is difficult to alter once recorded.

Think of it like a public notebook copied across many computers:

• Every time new information is added, it’s grouped into a block

• Each block is linked to the previous one using cryptography, forming a chain

• Copies of the chain are stored across many computers (“nodes”)

• Changes usually require agreement from the network, making tampering very hard

Core idea

Traditional databases are usually controlled by one organization:

• A bank controls its banking database

• A company controls its internal records

A blockchain distributes that control across many participants.

How it works

1. Someone requests a transaction
   Example: sending cryptocurrency

2. The transaction is broadcast to the network

3. Network participants validate it
   Depending on the blockchain, this may use systems like:

   • Proof of Work

   • Proof of Stake

4. Valid transactions are bundled into a block

5. The block is added to the chain permanently

6. Everyone’s copy of the ledger updates

Key features

Decentralization

No single authority fully controls the system.

Transparency

Many blockchains allow anyone to view transaction history.

Immutability

Once data is added, changing it is extremely difficult because every linked block would also need modification.

Security

Cryptography helps protect the records and verify ownership.

Common uses

Cryptocurrencies

The best-known example is Bitcoin. Others include Ethereum.

Smart contracts

Programs that automatically execute when conditions are met, commonly associated with Ethereum.

Supply chains

Tracking products from manufacturing to delivery.

Digital identity

Verifying identity without relying on a central database.

NFTs

Unique digital ownership records for art, collectibles, and media.

Simple analogy

Imagine a Google Doc shared with thousands of people:

• Everyone can see updates

• Nobody can secretly rewrite history

• Every change is tracked

• Copies exist everywhere

Blockchain applies a similar idea to transactions and digital ownership, but with cryptographic security and consensus rules.

Important limitations

Blockchain is not automatically:

• Fast

• Cheap

• Private

• Energy-efficient

Some blockchain systems can be slow or expensive, and not every problem benefits from decentralization.

Difference between blockchain and Bitcoin

• Blockchain = the underlying technology

• Bitcoin = one application built using blockchain technology

A useful comparison:

• Blockchain is like the internet

• Bitcoin is like one website running on it