At the heart of Ethereum is the Ethereum Virtual Machine, or EVM. Think of it as a single, global computer that runs on thousands of machines (nodes) around the world. Every full node on the network runs the EVM to maintain consensus across the blockchain. Its job is to process the state changes that happen on the network.

When developers write smart contracts, they typically use a high-level language like Solidity. This code is then compiled down into something called bytecode, which is the machine language the EVM can understand and execute.

The EVM is completely isolated from the main network, meaning code running inside it has no access to your computer's file system or network. This creates a secure sandbox for running untrusted code from anyone in the world.

Every single operation that runs on the EVM has a cost. This cost is measured in "gas." Simple operations, like adding two numbers, cost very little gas. More complex ones, like storing data on the blockchain, cost significantly more. Users pay for this gas with ETH, which prevents the network from being clogged with spammy or infinite loops and compensates the people running the nodes.

The Ethereum network is made up of thousands of computers called nodes. Each node runs client software that verifies all transactions and blocks, ensuring they follow the network's rules. This distributed network is what makes Ethereum decentralized and censorship-resistant. Without nodes, there is no blockchain.

There are a few different types of nodes, each with a distinct role. The main difference between them is how much blockchain data they download and store.

Full nodes are the backbone of the network. They download and validate every block and transaction, enforcing the consensus rules. Light nodes offer a lower-resource alternative by only downloading block headers and requesting other information from full nodes as needed. Archive nodes are a type of full node that builds an archive of all historical states of the blockchain, which is useful for services that need to query past data, like Etherscan.

For a decentralized network to function, all participants must agree on the current state of the blockchain. This agreement is achieved through a consensus mechanism. It's the set of rules that determines who gets to add the next block of transactions to the chain.

Historically, Ethereum used a system called Proof of Work (PoW), the same mechanism that powers Bitcoin. In PoW, powerful computers known as miners compete to solve a complex mathematical puzzle. The first one to find the solution gets to create the next block and is rewarded with new ETH.

In 2022, Ethereum underwent a major upgrade known as "The Merge," transitioning its consensus mechanism to Proof of Stake (PoS). Under PoS, the concept of miners is replaced with validators. Instead of running powerful hardware, validators stake a significant amount of ETH as collateral to get the chance to create a new block. If they act honestly and validate transactions correctly, they receive a reward. If they act maliciously, they risk losing their staked ETH.

This change drastically reduced Ethereum's energy consumption by over 99% and altered the economic incentives for securing the network.

Now that you understand the core architecture of Ethereum, let's review the key terms.

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Understanding these architectural components—the EVM as the computation engine, nodes as the keepers of the network, and the consensus mechanism as the rulebook—is the foundation for building on Ethereum.