📌 Storage

• Storage is the permanent place on the blockchain.
• It is tied to the contract’s state variables.
• Changes here persist between transactions.
• Storage writes are expensive in gas because data is written to the blockchain forever.
• Reading storage is cheaper than writing, but still costs more than reading from memory or calldata.

Example:

uint public x; // this variable is in storage

function update() public {
    x = 5; // writes to storage (permanent)
}

✅ Think of storage as the hard disk of the contract.

📌 Memory

• Memory is a temporary read–write area
• It only exists while a function is executing
• Once the function ends, the memory data is wiped
• It is cheaper than storage, but more expensive than calldata
• You can modify memory variables freely

Example:

function copy(uint[] memory arr) public pure returns (uint) {
    arr[0] = 10; // OK, can modify
    return arr[0];
}

✅ Think of memory as RAM in your function.