What is the difference between Audi A8 FSI and TFSI engines?

I'm looking at purchasing an Audi A8 and I noticed that some models have FSI engines while others have TFSI engines. What is the difference between these two and what should I know before making a decision?

The main difference between FSI and TFSI engines is the way they inject fuel into the combustion chamber. FSI (fuel stratified injection) engines use a direct injection system, while TFSI (turbo fuel stratified injection) engines use both direct injection and turbocharging. This allows TFSI engines to produce more power and better performance compared to FSI engines.