Bytecode

What is Bytecode?

Bytecode is the low-level, hexadecimal machine code that a smart contract is compiled into before being deployed. It is the only language that a blockchain's virtual machine (like the EVM) can actually read and execute.

How does Bytecode work?

1. A developer writes a smart contract in a high-level language like Solidity.
2. A compiler (e.g., solc) translates this source code into bytecode.
3. The bytecode is sent to the blockchain as part of a "contract creation" transaction.
4. The blockchain stores this bytecode at a specific address on the ledger.
5. When a user calls a function, the EVM executes the bytecode line-by-line to perform the logic.

Why does Bytecode matter?

Bytecode is the source of truth for a smart contract's behavior. While human-readable source code can be verified on sites like Etherscan, the bytecode is what actually manages the funds and logic on-chain.

Key features of Bytecode

• Hexadecimal format (e.g., 0x60806040...)
• Machine-readable only
• Permanent and immutable once deployed
• Deterministic output from source code
• Executed by the Ethereum Virtual Machine (EVM)

Examples of Bytecode

• A "Contract Creation" transaction containing the initialization bytecode.
• The "Runtime Bytecode" that remains on-chain after a contract is deployed.
• Opcodes like PUSH1, SSTORE, and REVERT, which are the human-readable labels for bytecode instructions.