Introduction

Chapter 1: Introduction to Blockchain Technology

Overview

Blockchain technology is a decentralized, distributed ledger system that records transactions across multiple computers in a way that makes them resistant to modification. Understanding blockchain fundamentals is essential for anyone working with blockchain nodes, as nodes are the infrastructure that powers these decentralized networks.

1.1 What is Blockchain?

A blockchain is a distributed database that is shared among the nodes of a computer network. It stores information electronically in digital format. Blockchains are best known for their crucial role in cryptocurrency systems, such as Bitcoin and Ethereum, for maintaining a secure and decentralized record of transactions.

Key Characteristics

Characteristic	Description
Decentralization	No single entity controls the network
Transparency	Transactions are visible to all participants
Immutability	Once recorded, data cannot be easily altered
Security	Cryptographic hashing ensures data integrity
Consensus	Network participants agree on the valid state

1.2 How Blockchain Works

The Block Structure

Each block in a blockchain contains:

┌─────────────────────────────────────────┐
│              BLOCK HEADER                │
├─────────────────────────────────────────┤
│  Version      │ 4 bytes                  │
│  Previous    │ 32 bytes (hash)         │
│  Hash        │                          │
│  Merkle      │ 32 bytes (hash)          │
│  Root        │                          │
│  Timestamp   │ 4 bytes                  │
│  Difficulty  │ 4 bytes                  │
│  Nonce       │ 4 bytes                  │
├─────────────────────────────────────────┤
│           TRANSACTION DATA               │
│  (Variable size, typically 1MB limit)  │
└─────────────────────────────────────────┘

The Chain

Blocks are linked together through cryptographic hashes:

┌──────────┐    ┌──────────┐    ┌──────────┐    ┌──────────┐
│ Block 1  │───▶│ Block 2  │───▶│ Block 3  │───▶│ Block 4  │
│ Prev: 0  │    │ Prev: H1 │    │ Prev: H2 │    │ Prev: H3 │
│ Hash: H1 │    │ Hash: H2 │    │ Hash: H3 │    │ Hash: H4 │
└──────────┘    └──────────┘    └──────────┘    └──────────┘

1.3 Consensus Mechanisms

Consensus mechanisms are protocols that ensure all nodes in a blockchain network agree on a single version of truth. Here are the main types:

Proof of Work (PoW)

Miners compete to solve complex mathematical puzzles. The first to solve it gets to add the next block.

Examples: Bitcoin, Ethereum (legacy)
Pros: Highly secure, battle-tested
Cons: Energy-intensive, slower throughput

Proof of Stake (PoS)

Validators stake their cryptocurrency as collateral to propose and validate blocks.

Examples: Ethereum (after The Merge), Cardano, Solana
Pros: Energy-efficient, faster finality
Cons: Security concerns about centralization

Delegated Proof of Stake (DPoS)

Token holders vote for a small number of delegates who validate transactions on their behalf.

Examples: EOS, Tron, Cosmos
Pros: High throughput, efficient
Cons: More centralized

Practical Byzantine Fault Tolerance (PBFT)

A consensus algorithm where a leader proposes blocks and validators vote on them.

Examples: Hyperledger Fabric, Cosmos (Tendermint)
Pros: Fast finality, Byzantine fault tolerance
Cons: Limited scalability

1.4 Blockchain Layers

Layer 1 (L1)

The base blockchain protocol - the fundamental infrastructure.

Examples: Bitcoin, Ethereum, Cosmos
Characteristics: Full node validation, consensus participation

Layer 2 (L2)

Scaling solutions built on top of Layer 1.

Examples: Lightning Network (Bitcoin), Optimism, Arbitrum (Ethereum)
Characteristics: Off-chain transaction processing, rollups

Layer 0

Infrastructure layer that supports L1 blockchains.

Examples: Polkadot, Cosmos SDK
Characteristics: Cross-chain interoperability

1.5 Key Blockchain Concepts

Smart Contracts

Self-executing contracts with terms directly written into code. They automatically enforce and execute when predetermined conditions are met.

// Example: Simple Smart Contract
contract SimpleStorage {
    uint256 private value;

    function set(uint256 _value) public {
        value = _value;
    }

    function get() public view returns (uint256) {
        return value;
    }
}

Gas

A measurement of computational work required to execute operations on the network.

Ethereum: Gas limits, gas prices (Gwei)
Solana: Compute units
Cosmos: Gas fees

Tokens

Digital assets created on existing blockchains:

Fungible Tokens: Interchangeable (like currency)
Non-Fungible Tokens (NFTs): Unique, indivisible

Wallets

Software that allows users to interact with blockchain networks:

Hot Wallets: Connected to the internet
Cold Wallets: Offline storage (hardware wallets)

1.6 Major Blockchain Ecosystems

Ethereum

The most popular smart contract platform with the largest ecosystem of dApps (decentralized applications).

Consensus: Proof of Stake (Beacon Chain)
Token: ETH
EVM: Ethereum Virtual Machine compatible

Cosmos

An ecosystem of interconnected, sovereign blockchains using the Cosmos SDK.

Consensus: Tendermint BFT
Token: ATOM
IBC: Inter-Blockchain Communication protocol

Solana

High-performance blockchain known for fast transaction processing.

Consensus: Proof of History + Proof of Stake
Token: SOL
Speed: 65,000 TPS theoretically

Bitcoin

The first and largest cryptocurrency by market cap.

Consensus: Proof of Work
Token: BTC
Use Case: Digital gold, payments

1.7 Understanding Blockchains Visually

┌─────────────────────────────────────────────────────────────────────┐
│                    BLOCKCHAIN NETWORK OVERVIEW                     │
├─────────────────────────────────────────────────────────────────────┤
│                                                                     │
│    ┌─────────┐     ┌─────────┐     ┌─────────┐     ┌─────────┐     │
│    │  Node A │     │  Node B │     │  Node C │     │  Node D │     │
│    │ (Miner) │     │(Validator)    │(Full Node)    │(Light)  │     │
│    └────┬────┘     └────┬────┘     └────┬────┘     └────┬────┘     │
│         │              │              │              │           │
│         └──────────────┴──────────────┴──────────────┘           │
│                              │                                     │
│                     ┌────────▼────────┐                           │
│                     │   P2P NETWORK   │                           │
│                     │  (libp2p/discover)                          │
│                     └────────┬────────┘                           │
│                              │                                     │
│         ┌────────────────────┼────────────────────┐               │
│         │                    │                    │               │
│    ┌────▼────┐         ┌─────▼─────┐        ┌─────▼─────┐         │
│    │ BLOCK 1 │         │  BLOCK 2  │        │  BLOCK 3  │         │
│    │ Hash:H1 │────────▶│ Hash:H2   │───────▶│ Hash:H3   │         │
│    └─────────┘         └───────────┘        └───────────┘         │
│                                                                     │
└─────────────────────────────────────────────────────────────────────┘

1.8 Why Blockchain Nodes Matter

Blockchain nodes are the backbone of any blockchain network. They:

Validate Transactions: Ensure all transactions follow network rules
Maintain Consensus: Help the network agree on the state of the blockchain
Store Blockchain Data: Keep a complete copy of the blockchain
Broadcast Information: Propagate transactions and blocks to other nodes
Enable Decentralization: Make the network resistant to censorship

1.9 Interview Quick Facts

Question	Answer
What is a blockchain?	A distributed, immutable ledger that records transactions across multiple computers
What makes blockchain secure?	Cryptographic hashing, consensus mechanisms, and decentralization
Difference between L1 and L2?	L1 is the base layer; L2 builds on top for scalability
What is consensus?	The process by which nodes agree on the valid state of the blockchain
Why is decentralization important?	It ensures no single point of failure and resistance to censorship

Summary

Blockchain is a decentralized, distributed ledger technology
Blocks are cryptographically linked together
Various consensus mechanisms (PoW, PoS, DPoS, PBFT) secure the network
Major ecosystems include Ethereum, Cosmos, Solana, and Bitcoin
Understanding blockchain fundamentals is crucial for node operations

Next Chapter

In Chapter 2: What is a Blockchain Node?, we’ll dive deep into understanding what blockchain nodes are, their role in the network, and how they communicate.

Last Updated: 2026-02-20