Answer from cs61c-cf (Aspandiar Dahmubed 16812056) for Question 2
A subnormal is a floating point number that has the same exponenet as 0 but a nonzero significand. They allow a number to degrade in significance until it becomes 0, called gradual underflow. Rather than having a gap between 0 and the smallest normalized number, IEEE allows denormalized numbers. 
If our programs do not expect subnormals, it could cause an exception.