Answer from cs61c-ec (Osbert Orr 16671538) for Question 2
Subnormal numbers fill the gap around zero in floating point arithmetic. Any non-zero number which is smaller than the smallest normal number is considered to be subnormal.

Some implementations of a floating point unit do not directly support subnormal numbers in hardware, but rather trap to some kind of software support. While this may be transparent to the user, it can result in calculations which produce or consume denormal numbers to be much slower than similar calculations on normal numbers.