Throttle-body injection systems were some of the first to be used as the carburetor disappeared from the assembly line. This system easily fit into the previous carburetor system and was relatively inexpensive. Throttle body injection disappeared in the early nineties in favor of better systems, such as the central port injection system, which feed fuel to the system at the same time at each cylinder. In time these have since been replaced by multi-port fuel injection, which provides injection at each cylinder according to its individual fuel needs. Direct injection is yet another variation that is commonly found in diesel engines.