Ethereum Architecture: EVM, Gas, Accounts & Merge

Section 01

Ethereum — The World Computer

📖 Real World Analogy

From A Calculator To A Global Computer

Imagine Bitcoin as a worldwide calculator — brilliant at one thing: tracking who owns how much money. Now imagine someone asks, "What if this shared machine could run any program, not just move coins?" That question, asked by a 19-year-old named Vitalik Buterin in 2013, gave birth to Ethereum.

Ethereum is not just digital money — it is a global, shared computer that no one owns and no one can shut down. Thousands of machines around the planet run the same programs, called smart contracts, and all agree on the results. Where Bitcoin stores value, Ethereum stores value and logic. It turned the blockchain from a ledger into a programmable platform — the foundation for DeFi, NFTs, DAOs, and thousands of applications.

Launched in 2015, Ethereum introduced a revolutionary idea: a blockchain with a built-in virtual machine that can execute code. This tutorial dissects its full architecture — the EVM, accounts, gas, Ether, transactions, blocks, nodes, the historic Merge to Proof of Stake, and the vast ecosystem it powers.

Diagram — Bitcoin vs Ethereum At A Glance

Bitcoin is a purpose-built ledger for money. Ethereum is a general-purpose computer that also happens to have money built in.

Section 02

The Ethereum Virtual Machine (EVM)

At the heart of Ethereum sits the Ethereum Virtual Machine (EVM) — a single, global, sandboxed computer replicated across every node. When you run a smart contract, every node executes the exact same instructions on its own copy of the EVM and arrives at the exact same result. This is what makes the outcome trustless: no one has to trust the result because everyone independently computes it.

Animated Diagram — Every Node Runs The Same EVM

The EVM is deterministic: the same input always produces the same output on every node. That's why thousands of machines can agree on the result without a central authority.

🌐

Global & Singular

one shared machine

There is conceptually just one EVM, whose state is mirrored on every node. Its "memory" is the shared world state of all accounts and contracts.

🔒

Sandboxed

isolated & safe

Contract code runs in a walled-off environment. It cannot touch the network, filesystem, or other processes — only the blockchain state.

🔢

Deterministic

same in, same out

No randomness, no clocks, no external calls that could differ. Given identical input, every EVM everywhere computes an identical result.

🏗️

Turing-Complete — With A Safety Valve

Unlike Bitcoin Script, the EVM is Turing-complete — it can run loops and arbitrary logic. But that raises a danger: an infinite loop could freeze every node forever. The solution is gas (next section): every operation costs gas, and when the gas runs out, execution halts. Turing-completeness with a built-in circuit breaker.

Section 03

Accounts — Two Kinds Of Actors

Ethereum tracks accounts, not UTXOs like Bitcoin. Your balance is a single number that goes up and down, just like a bank account. There are two distinct account types, and knowing the difference is essential.

👤 Externally Owned Account (EOA)

Controlled by a private key

Owned by a human / wallet

Can start transactions

Has a balance, no code

Example: your MetaMask

🤖 Contract Account

Controlled by its own code

Deployed to the blockchain

Only reacts, never self-starts

Has a balance AND code + storage

Example: a Uniswap contract

Animated Diagram — EOA Triggers A Contract

Every transaction begins with a human-controlled EOA. Contracts are passive — they only run when called, but once triggered they can call each other in complex chains.

📋 What Every Account Stores

Nonce

A counter of how many transactions this account has sent (EOAs) or contracts it has created. Prevents replay and enforces order.

Balance

The amount of Ether the account holds, measured in wei (1 ETH = 10¹⁸ wei).

Code Hash

For contracts: a hash of the account's EVM bytecode. For EOAs: empty.

Storage Root

For contracts: the root hash of the account's persistent key-value storage. For EOAs: empty.

Section 04

Ether (ETH) — The Fuel And The Money

Ether (ETH) is Ethereum's native cryptocurrency. It plays two roles: it is money you can send and hold, and it is the fuel that pays for computation on the network. Every action — a transfer, a swap, minting an NFT — is paid for in ETH.

Diagram — Denominations Of Ether

Like dollars and cents, Ether has sub-units. Gwei (a billionth of an ETH) is the unit you'll see when paying gas fees.

⛽

ETH As "Fuel" — The Core Metaphor

Think of the EVM as an engine and ETH as its fuel. Just as a car can't move without petrol, no computation happens on Ethereum without ETH to pay for it. This isn't a bug — it's the mechanism that stops spam, rewards validators, and forces users to value the network's limited computing resources. Every keystroke of computation has a price.

Section 05

Gas — Paying For Computation

Gas is the unit that measures how much computational work a transaction requires. Every EVM operation has a fixed gas cost — a simple transfer costs 21,000 gas; a complex smart contract call costs far more. You pay for gas in ETH. Gas is what makes the "world computer" economically sustainable and spam-resistant.

Animated Diagram — How A Gas Fee Is Calculated

Fee = gas used × gas price. Since EIP-1559 (2021), the "base fee" portion is permanently burned (destroyed), while the "tip" rewards the validator who includes your transaction.

⛽ Key Gas Terms

Gas Limit

The maximum gas you're willing to spend. A simple transfer needs 21,000; set too low and the tx fails (but you still pay for work done).

Base Fee

A network-set minimum price per gas that rises when the network is busy. Since EIP-1559 it is burned, reducing ETH supply.

Priority Fee (Tip)

An extra amount you add to incentivize validators to include your tx faster during congestion.

Max Fee

The absolute most you'll pay per gas. Any difference between max fee and (base + tip) is refunded to you.

🔥

EIP-1559 — Why Ethereum Burns ETH

In August 2021, the London upgrade introduced EIP-1559, which burns the base fee of every transaction. During busy periods, more ETH can be burned than is created, making Ether deflationary. This "ultrasound money" mechanism ties the value of ETH directly to network usage — the more Ethereum is used, the more ETH disappears forever.

Section 06

Transactions — Instructions To The World Computer

An Ethereum transaction is a signed instruction from an EOA. It can be a simple ETH transfer, a call to a smart contract, or the deployment of a new contract. Every transaction changes the global state and must be paid for in gas.

💸

Transfer

move ETH

Send ETH from one account to another. The simplest transaction, always costing exactly 21,000 gas.

📱

Contract Call

run a function

Invoke a function on an existing contract — swap tokens, vote in a DAO, mint an NFT. Gas cost depends on the work done.

🔧

Deployment

create a contract

Upload new bytecode to the blockchain, creating a contract account. The most expensive type, since code is stored forever.

📜 Fields Inside A Transaction

nonce

The sender's transaction count — ensures order and prevents replay.

The recipient address (an EOA, a contract, or empty for deployment).

value

How much ETH (in wei) to send along with the transaction.

data

Optional payload — the encoded function call and its arguments for contracts.

gas fields

Gas limit, max fee, and priority fee that define what you'll pay.

signature

The ECDSA signature (v, r, s) proving the sender authorized this transaction.

Section 07

Blocks — Bundles Of State Changes

Ethereum groups transactions into blocks, produced roughly every 12 seconds (much faster than Bitcoin's 10 minutes). Each block links to the previous one and commits to the new world state — the up-to-date balances and storage of every account after the block's transactions run.

Animated Diagram — Transactions Update The World State

Think of Ethereum as a state machine. Each block takes the current world state, applies its transactions through the EVM, and produces the next world state.

Property	Bitcoin	Ethereum
Block time	~10 minutes	~12 seconds
Accounting	UTXO model	Account/balance model
Block contains	Transactions	Transactions + world state root
Programmability	Limited Script	Full smart contracts
Consensus	Proof of Work	Proof of Stake (since 2022)

Section 08

Nodes — The Machines That Run Ethereum

Ethereum runs on tens of thousands of nodes worldwide. Since the Merge, each full node actually runs two pieces of software working together: an execution client (which runs the EVM and processes transactions) and a consensus client (which handles Proof of Stake and block agreement).

Diagram — The Two Halves Of A Modern Ethereum Node

Since the Merge, a full node pairs an execution client (the EVM engine) with a consensus client (Proof of Stake), talking over the Engine API.

🖥️

Full Node

verifies everything

Stores recent state and validates every block and transaction independently. The backbone of the network's honesty.

📦

Archive Node

full history

A full node that also keeps every historical state — terabytes of data. Used by explorers and analytics services.

🧠

Validator Node

stakes 32 ETH

A full node running a consensus client with 32 ETH staked, actively proposing and attesting to blocks to earn rewards.

Section 09

The Ethereum Merge — Switching The Engine Mid-Flight

📖 A Historic Moment

Changing A Plane's Engine While It Flies

On 15 September 2022, Ethereum did something never done before: it swapped its entire consensus mechanism from Proof of Work to Proof of Stake — live, without stopping, on a network securing hundreds of billions of dollars. Engineers compared it to changing a jet engine mid-flight without the passengers noticing.

The result was staggering. Ethereum's energy consumption dropped by roughly 99.95% overnight — the equivalent of a small country's electricity use simply vanishing. Miners were replaced by validators, and the network became vastly greener while staying fully operational. It remains the largest consensus migration in blockchain history.

Animated Diagram — Before And After The Merge

The Merge replaced energy-hungry mining with efficient staking, cutting Ethereum's power use by ~99.95% while the network kept running without interruption.

🌱

What The Merge Did — And Didn't — Change

It changed: the consensus mechanism (PoW → PoS), energy use (down 99.95%), and new issuance (far less ETH created). It did NOT change: gas fees, transaction speed, or capacity — those are tackled by later upgrades and Layer-2 rollups. A common myth is that the Merge made Ethereum cheaper or faster; it didn't. It made it sustainable.

Section 10

The Ethereum Ecosystem — What It Powers

Because Ethereum can run any program, an entire universe of applications has grown on top of it. These decentralized applications (dApps) use smart contracts to recreate — and reinvent — finance, art, ownership, and organizations without middlemen.

🏦

DeFi

Decentralized Finance — lending, borrowing, and trading without banks. Uniswap, Aave, and MakerDAO let anyone access financial services with just a wallet.

Uniswap, Aave, Compound

🎨

NFTs

Non-Fungible Tokens prove unique digital ownership — art, collectibles, music, game items. The ERC-721 standard made verifiable digital scarcity possible.

OpenSea, ERC-721

🤝

DAOs

Decentralized Autonomous Organizations — internet-native communities that govern shared funds and rules by on-chain voting instead of a boardroom.

on-chain governance

🪙

Stablecoins

Tokens pegged to real currencies like the US dollar. USDC and DAI bring price stability to crypto and power most on-chain trading and payments.

USDC, DAI, USDT

📡

Layer-2 Rollups

Scaling networks that batch thousands of transactions off-chain and settle on Ethereum. Arbitrum, Optimism, and Base slash fees while inheriting Ethereum's security.

Arbitrum, Optimism, Base

🧩

Token Standards

Shared blueprints like ERC-20 (fungible tokens) let any developer create interoperable assets that work in every wallet and exchange instantly.

ERC-20, ERC-1155

🧩

"Money Legos" — Why Composability Matters

Ethereum apps are often called money legos because they snap together. A single transaction can borrow from Aave, swap on Uniswap, and deposit into a yield vault — all composed like building blocks, because every contract can call every other contract. This permissionless composability is Ethereum's superpower and the reason its ecosystem compounds so quickly.

Section 11

Golden Rules — Ethereum Architecture

♦ Non-Negotiable Truths

Ethereum is a world computer, not just money. The EVM lets it run arbitrary programs, turning the blockchain from a ledger into a programmable platform.

The EVM is deterministic and replicated. Every node runs the same code and gets the same result — that's how thousands of machines reach consensus on computation.

There are two account types. EOAs (controlled by keys, can start transactions) and contract accounts (controlled by code, only react). Only EOAs initiate.

Gas is the circuit breaker. Every operation costs gas paid in ETH; when gas runs out, execution stops. This is what makes Turing-completeness safe.

EIP-1559 burns the base fee. Heavy network use can destroy more ETH than is created, making Ether potentially deflationary.

A block is a state transition. Old world state + transactions, run through the EVM, equals the new world state — a giant shared state machine.

Modern nodes have two halves. An execution client (EVM) and a consensus client (Proof of Stake), working together since the Merge.

The Merge made Ethereum sustainable, not cheaper. It cut energy ~99.95% by switching to PoS, but fees and speed are addressed by Layer-2 rollups instead.