Drive by wire means that you are asking a controller's permission to go faster when you step on it. You still have a cable but that cable does not go to a traditional carb. Back in the old days the only thing the throttle did was open up the butterfly so that more air could go in the air pump (engine) taking more fuel with it. Now a days the fuel is injected under force by an electronically controled injector. A sensor monitors throttle position and gives the car more gas when you step on it. The carb is replaced with a throttle body that supplies the air to the engine.