The idea of rapid shifting by clutch alone has also been developed as the dual-clutch transmission, in recent high-performance cars. This combines the simplicity of a shifting gearbox with the rapid shifts of a clutch-based design. There are effectively two separate gearboxes, each offering alternate ratios from the overall set, and the two clutches select which gearbox is in effect. Changes within the gearbox are done automatically, to predict which ratio the driver will require next. Provided that the next ratio has been selected correctly (i.e. the computer guessed correctly as to an up-shift vs. a down-shift) the shift itself is merely a rapid movement of the clutch. Unexpected shifts may confuse the system though and it must first select the correct ratio before engaging the clutch, giving a far slower shift.