What is the difference between quattro and xDrive in Audi and BMW cars?

I'm looking into getting a luxury car and I've narrowed it down to Audi and BMW. I keep hearing about their respective all-wheel drive systems - quattro and xDrive - but I'm not sure what the difference is. Can someone explain?

Both quattro and xDrive are all-wheel drive systems used in Audi and BMW cars respectively. The main difference is that quattro is a full-time all-wheel drive system, meaning all four wheels are constantly receiving power and working together, while xDrive is a part-time all-wheel drive system that primarily operates in rear-wheel drive mode until it detects a loss of traction in the rear wheels, at which point it sends power to the front wheels. In terms of performance and handling, quattro provides better overall traction and stability, while xDrive offers better handling and agility.