Level 1 · Module 1.1

Anatomy of a Blockchain

Imagine a shared notebook where every page is sealed and linked to the one before it. Change one word and the entire book falls apart. That's the core idea behind blockchain — and it changes everything about trust.

⏱ 8 min read 🟢 Beginner 📖 4 sections

01 What is a Block?

A blockchain is made of blocks — and a block is exactly what it sounds like: a container of data. Every block holds three fundamental elements that work together to make the system tamper-proof.

DATA

The transactions recorded in that block. Example: "Alice sent 0.5 BTC to Bob". A single block can contain hundreds or thousands of transactions.

HASH

A unique fingerprint generated from the block's data. It's always 64 characters long. Change even one letter in the data and the hash becomes completely different.

PREV HASH

The hash of the block that came before it. This is what links all the blocks into a chain — and what makes the whole structure tamper-evident.

Analogy — The Security Chain

Think of a row of numbered safes, each holding its combination and the number of the previous safe. If you crack open safe #5 and change something, every combination from #6 onwards becomes wrong — and everyone notices immediately. Recalculating all subsequent safes is computationally impossible.

02 The Distributed Ledger

Here's where blockchain becomes truly revolutionary. A regular database lives on servers owned by a single company — a bank, a government, a corporation. They can edit it, freeze it, or shut it down. Blockchain is different.

Thousands of computers worldwide — called nodes — each hold an identical copy of the entire blockchain. To alter any record, you would need to simultaneously modify the majority of all nodes on Earth. That's why blockchain is described as:

DECENTRALISED

No single entity owns or controls it. There's no CEO who can reverse a transaction or freeze your account.

TRANSPARENT

On public blockchains, anyone can read every transaction ever made — from the very first block to the one created a second ago.

IMMUTABLE

What has been written cannot be changed or deleted. The history is permanent.

03 The Three Types of Nodes

A node is simply a computer participating in the network. Not all nodes are equal — they play different roles:

FULL NODE

Holds a complete copy of the blockchain from block #1 to today. Independently verifies every transaction. The backbone of the network's security.

LIGHT NODE

Holds only a summary of the blockchain. Lighter and faster, but relies on full nodes for deep verification. Used in most mobile wallets.

VALIDATOR

Proposes new blocks and adds them to the chain. They earn fees for this work, and risk losing their stake if they misbehave (more on this in Module 1.2).

04 Why This Matters

Before blockchain, if two people who don't know each other wanted to transact, they needed a trusted middleman — a bank, a notary, PayPal. That middleman charges fees, can refuse service, can freeze funds, and can fail.

Blockchain replaces the middleman with mathematics. The rules are written in code, enforced automatically, and visible to everyone. You don't trust the other person — you trust the protocol.

The true innovation of blockchain is not technical: it's the ability to create trust between strangers without needing any intermediary — no bank, government, or notary required.

1.2 Consensus Mechanisms →