> For the complete documentation index, see [llms.txt](/llms.txt).

This module explains how transactions flow through the network, what gas is, and how the Ethereum Virtual Machine (EVM) executes smart contracts.

## Gas, Transactions, and Blocks

Every transaction must pay **gas** to compensate miners/validators.\
For EVM chains like Rootstock, gas is paid in rBTC.

A transaction flows through three steps:

1. Submitted to the network
2. Picked up by miners
3. Included in a block

### Transaction Components

| Field      | Description                        |
| ---------- | ---------------------------------- |
| `from`     | Sender address                     |
| `to`       | Recipient address (or contract)    |
| `value`    | Amount of rBTC to send             |
| `data`     | Contract call data (if applicable) |
| `gasLimit` | Maximum gas units to spend         |
| `gasPrice` | Price per gas unit                 |

### Gas Calculation

```
Transaction Cost = Gas Used × Gas Price
```

If a transaction runs out of gas, it reverts but you still pay for the gas consumed.

## EVM Overview

The **Ethereum Virtual Machine (EVM)** is a runtime environment for executing smart contracts.

Key concepts:

- **Bytecode execution** — Contracts compile to bytecode
- **Storage, memory, stack** — Different data locations
- **Opcodes** — Low-level instructions
- **Contract ABI** — Application Binary Interface for function calls

Rootstock is fully EVM-compatible, so Ethereum tools work with minimal or zero modification.

## Bitcoin vs EVM Smart Contracts

Rootstock merges Bitcoin's security guarantees with Ethereum-compatible smart contracts.

| Feature         | Bitcoin                  | EVM-Compatible Chains |
| --------------- | ------------------------ | --------------------- |
| Smart Contracts | Limited (Bitcoin Script) | Full Solidity support |
| Token Standard  | None                     | ERC-20, ERC-721, etc. |
| VM              | Bitcoin Script           | EVM                   |
| Strength        | Security, finality       | Programmability       |

Rootstock sits at the intersection: **Bitcoin-backed security + EVM programmability.**

:::tip[Understanding Gas Differences]

Read more about [Gas differences on Rootstock](/developers/blockchain-essentials/overview/#gas-differences).

:::

## Summary

Before moving forward, ensure you understand:

- How blockchains maintain shared state
- How keys, wallets, and addresses work
- What gas is and why it's required
- How the EVM executes smart contracts

**Next:** [Rootstock Architecture](/developers/blockchain-essentials/rootstock-essentials/rootstock-architecture/)