Then, if a car Has both AT and MT, then how does the change of gears affect the movement of the clutch disc? Someone told me that in an example of the BMW 545, how does one, go about moving from one transmssion to another? (l hope l am clear)

l guess you are talking about the maula overide in auto mode, this is just down to some very clever electronics in a tiptronic box

very seamless process. just move the shifter into drive for auto, or over to manual, for up/down shifts.

There is only 1 transmission in the car,you are simply shifting tha auto trans manually insted of letting it shift automatically.It has a shifter with a dual gate pattern, the auto shift is when in drive and then in other gate you shift it up and down without any pedals just like downshifting or upshifting any auto trans.

l dont think they made a dual transmission for an automotbile in the US yet. The only ones l have seen is overseas. IF u r referring to like manual-shift like they have in some cars like Audi, BMW & some American cars, they r an automatic transmission because if there is one side of the shifter that has like a H or L or + or -, then l know what u r talking about. This makes the car either go into a higher or lower gear when u r cruising on the freeway, put it on + it will shift into a higher gear or - to go into a lower gear, but if u put into D ''drive gear'' it will shift automatically. But this option is on luxury model & sports cars. It is a nice way to intigrate a manual-like feeling when u r in a automatic car.