The VAG Direct Shift Gearbox - sometimes called the S-Tronic in the Audi range - is the world's first production dual clutch semi automatic gearbox. The system was developed for Audi by BorgWarner for use in the companies Audi TT 3.2V6, and was so well received it is now used in much of the Volkswagen Audi Group range.
The DSG is often compared to F1 style automated or robotic manual gearboxes, but differs in some very important ways.
The DSG gearbox is, however, not a new invention. The system was first designed by Andolphe Kégresse just before the second world war but because of the lack of technology, not to mention the war, he never produced a working version of the Dual Clutch Gearbox (DCG). The system was used by another German car company in the 80's though: Porsche used the PDK (Porsche Doppelkupplungs) system in their 956 and 962 Le Mans race cars, and Audi used the same system in the Sport Quatro S1. Porsche and Audi have a long history of technology sharing.
Both of these uses eventually faded, primarily because the computing technology that allows the system to work so effectively did not prove to be reliable enough in the tough and demanding world of the race car.
To understand how revolutionary the DSG gearbox is, first I will explain the F1 style systems. These differ in name depending on the manufacturer; Ferrari call theirs the F1 system, and BMW call theirs the SMG system.
These gearboxes all have one thing in common: they are just manual gearboxes, with a manual clutch that is operated by pneumatics. This method has many of the benefits the DSG box does. The gearbox itself weighs less: as the gear change is accurate, and no human mistakes can be made, the materials can be less hardy. They are also far more performant than the manual equivalent, both the BMW SMG II and the Ferrari F1 systems change cogs in around 80 milliseconds. This means that, while the gear is being shifted, all the power from the engine is waisted and a feeling of on-off-on is felt in the car as the pneumatics shift from in gear, to clutched, and then back into gear. The smoothness of this in the car depends on the software controlling it: for the fastest changes it can feel quite 'bumpy', similar to a bad gear change in a manual car. The only way of releaving this issue in the past was to fit a torque converter, this is the way that a standard auto box does it, and why it feels far smoother than any of the manual gearboxes produced. A torque converter, however, is very wasteful in terms of power, and usually very heavy.