quattro

A spreadsheet program marketed by Borland International in the late 1980s and early 1990s. Interest in Quattro plummeted after Lotus Development Corporation won its lawsuit against Borland for Quattro's violating Lotus 1-2-3's Look and Feel with its interface emulation and macro translation feature.

Borland sold Quattro, now called Quattro Pro to Novell in 1994. Novell put out a version of Quattro Pro for MS-DOS as late as 1995. Novell's website now states that Quattro Pro is "no longer supported by Novell".

Audi quattro (they insist on small letters) is a four-wheel drive technology that was created for rally conditions, nowadays applied in their flagship products with great success, most notably the TT quattro and S quattro cars.

Whereas most on-road cars are only driven by either their front wheels (almost all smallish cars) or their rear wheels (all "sporty" cars, bigger cars, e.g. most BMWs and Mercedes-Benz cars), Audi's premium cars have a drive system that takes the engine power to all four wheels, contributing towards better stability and traction on the road.

The first ever Audi quattro car took the world rally scene by storm in the 80s and is today considered to be one of crown jewels in Audi's Vorsprung Durch Technik philosophy.

At the heart of quattro ia s "torsen" (torque-sensing) intelligent differential that splits torque between the front and rear wheels based on the driving conditon. For example, if your front wheels were over snow, then quattro would send more power to the rear wheels to elliminate slip and improve traction.

It is also interesting to know that Audi's philosophy says that rear wheel drive is inherently unsafe and they only manufacture front-wheel drive and quattro cars. Audi also has a unique, enhanced front-wheel drive setup called FronTrack.

The secret to quattro lies in the center differential as pcholakov details above. These days it is implemented in one of two ways depending on engine configuration. Those cars which have a longitudinal engine configuration use a Torsen differential. Those with a transverse engine configuration use a Haldex clutch.

quattro systems with the Torsen differential have two EDL (electric differential lock) open differentials, one at the front and rear, and are known as quattro IV. quattro systems with the Haldex clutch have two EDL open differentials, however the default duty of the Haldex clutch is to provide no power to the rear wheels. When the front wheels begin to slip, the Haldex clutch will engage the rear wheels to compensate.

The Haldex system is found in Audi TTs, S3s and A3s, and also in the VW 4Motion Jetta and Golf.

You may hear people talking about full time quattro, in which case they're talking about the quattro IV system.