Storage vs Memory vs Calldata

Data location matters in Solidity: Storage is persistent (on-chain), like a hard drive — writes cost significant gas. Memory is temporary, exists only during function execution — like RAM. Calldata is read-only, used for function parameters in external calls — cheapest option. Reference types (arrays, structs, mappings) must specify their data location. Using `calldata` for read-only function parameters saves gas compared to `memory` because no copy is made.