In case of sliding mesh gearbox, the output shaft gears continually rotate While using the output shaft while in other gearbox, the output shaft gears are mounted with bearings hence these gears rotates independently. Twin-clutch automatic gearboxes started to appear in street autos in 2003, notably while in the Audi https://damienitfmr.dailyhitblog.com/39212889/a-review-of-gearbox-auto