There really is no difference except the fact that 911 is the class and the 996 is the chassis/generation number.
Two wheel drive and four wheel drive
Many differences, some of them are narrow bodies for the 911 carrera ans wide body for the "S".(Turbo style) More HP for the "S" than the normal carrera. options etc.
Porsche 911 because 911 has more ecceloration
Porsche 911 starts from....$85,400 to........$172,100
The 2014 Porsche 911 has 24 valves.
The 2012 Porsche 911 has 24 valves.
The 2002 Porsche 911 has 24 valves.
The 2006 Porsche 911 has 24 valves.
The 2005 Porsche 911 has 24 valves.
The 2009 Porsche 911 has 24 valves.
The 2004 Porsche 911 has 24 valves.
The 2011 Porsche 911 has 24 valves.