Bill please correct me if I am wrong....

Most DSLR's in the consumer ranger are not full frame DSLR's. That means the sensor is smaller than 35mm. Full Frame means the sensor is roughly the size of a 35mm film frame.

So if you took a 100mm Prime (no zoom) lens on a full frame DSLR it will have a much wider view than on a consumer DSLR. The 1.6 means it will act as a 160mm lens on a consumer DSLR. They also refer to these as CROP DSLR's. Think of it as in how you crop a photo.... Below is a quick illustration I made.