STARTGAS and GASPRICE are crucial for Ethereum's anti-denial of service model. In order to prevent accidental or hostile infinite loops or other computational wastage in code, each transaction is required to set a limit to how many computational steps of code execution it can use. The fundamental unit of computation is "gas"; usually, a computational step costs 1 gas, although some operations cost higher amounts of gas because they are more computationally complex, or increase the amount of data that must be stored as part of the state.