Opcode

At its lowest level, the EVM runs a sequence of opcodes — single-byte instructions that each do one thing.

Understanding opcodes reveals what your Solidity actually does and where gas goes.

An opcode (operation code) is a one-byte command the EVM executes. Examples include ADD, MUL, PUSH1, SLOAD, and JUMP.

Each opcode has a name, a numeric value, and a fixed gas cost.

Opcodes like PUSH, POP, DUP, and SWAP manage the stack.

PUSH adds a value, POP removes one, DUP duplicates an item, and SWAP exchanges two stack positions.

Arithmetic opcodes pop operands and push results: ADD, SUB, MUL, DIV, and MOD.

All math is done on 256-bit unsigned integers (with signed variants available).

Opcodes like LT, GT, EQ, AND, OR, and ISZERO handle comparisons and bitwise logic.

They push 1 for true and 0 for false, which control flow then uses.

Data movement opcodes touch the costly locations:

• MLOAD / MSTORE — read/write memory
• SLOAD / SSTORE — read/write storage

SSTORE is one of the most expensive opcodes.

JUMP and JUMPI (conditional jump) move execution to a JUMPDEST marker.

This is how the EVM implements loops and if-statements at the bytecode level.

Opcodes like CALLER, CALLVALUE, ADDRESS, and TIMESTAMP expose context.

For example, CALLER pushes the address that initiated the call (this is what msg.sender compiles to).

Every opcode has a defined gas cost. Cheap ones like ADD cost 3 gas; expensive ones like SSTORE cost up to 20000.

The total gas of a transaction is the sum of all opcodes it executes.

The Solidity compiler turns each high-level statement into many opcodes.

A single uint x = a + b; becomes PUSH, PUSH, ADD, and an MSTORE or SSTORE depending on where x lives.

Opcodes are the EVM's atomic instructions for stack, arithmetic, logic, memory, storage, control flow, and environment.

Each carries a gas cost, and your Solidity ultimately becomes a stream of them.

Test your opcode knowledge.

You learned that:

• Opcodes are one-byte EVM instructions
• They cover the stack, arithmetic, logic, memory, storage, control flow, and environment
• SSTORE is among the most expensive
• Solidity compiles into many opcodes

Next: accounts and state.