What is the difference between permanent Quattro and Ultra Quattro systems in Audi models?

I'm interested in purchasing an Audi and I've come across the terms 'permanent Quattro' and 'Ultra Quattro'. What do these mean and what is the difference between the two systems?

The permanent Quattro system is the traditional all-wheel drive system found in many Audi models. It distributes power to all four wheels at all times, providing excellent traction and stability on various road conditions.

The Ultra Quattro system is a newer, more efficient version of the permanent Quattro. It is able to disengage the rear wheels when not needed, reducing fuel consumption and improving handling. The system constantly monitors road conditions and can engage the rear wheels in just 250 milliseconds when necessary.

Both systems offer exceptional all-wheel drive capabilities and it ultimately depends on personal preference and driving needs. For everyday driving, the Ultra Quattro may provide better fuel efficiency, while the permanent Quattro would be more beneficial for off-roading or extreme weather conditions.