was connected to a vacuum-operated automatic clutch system. The top of the gear stick was designed to easily depress and activate an electric switch, i.e. when touched by the driver's hand. When pressed, the switch operated a 12-volt solenoid, which in turn operated the vacuum clutch actuator, thus disengaging the clutch and allowing shifting between gears. With the driver's hand removed from the gearshift, the clutch would re-engage automatically. The transmission was also equipped with a torque converter, allowing the car to idle in gear like with an automatic, as well as stop and start from a standstill in any gear. Automated manual transmissions Starting in the late 1990s, automotive manufacturers introduced what is now called an automated manual transmission (AMT), which is mechanically similar to, and has its roots in, earlier clutchless manual transmission systems. An AMT functions in the same way as older semi-automatic and clutchless manual transmissions, but with two exceptions; it is able to both operate the clutch and shift automatically, and does not use a torque converter. Shifting is done either automatically from a transmission control unit (TCU), or manually from either the shift knob or shift paddles mounted behind the steering wheel. AMTs combine the fuel efficiency of manual transmissions with the shifting ease of automatic transmissions. Their biggest disadvantage is poor shifting comfort due to the mechanical clutch being disengaged by the TCU, which is easily noticeable as "jolting". Some transmission makers have tried solving this issue by using oversized synchronizer rings and not fully opening the clutch during shifting—which works in theory, but as of 2007, there have not been any series production cars with such functions. In passenger cars, modern AMTs generally have six speeds (though some have seven) and a rather long gearing. In combination with a smart-shifting program, this can significantly reduce fuel consumption. In general, there are two types of AMTs: integrated AMTs and add-on AMTs. Integrated AMTs were designed to be dedicated AMTs, whereas add-on AMTs are conversions of standard manual transmissions into AMTs. An automated manual transmission may include a fully automatic mode where the driver does not need to change gears at all. These transmissions can be described as a standard manual transmission with an automated clutch and automated gear shift control, allowing them to operate in the same manner as traditional automatic transmissions. The TCU automatically shifts gears if, for example, the engine is