Forged calipers are made from the same material as standard calipers but instead of being cast using molten alloy the alloy solid,but very hot, and pressed under very high pressure into shape.This makes them very strong and makes sure there are no air holes or cracks in the material.
Radial calipers are mounted to the fork leg with the bolts pulling the caliper down onto the fork leg. Normal calipers bolt sideways onto the fork. The Idea is to stop the caliper from moving and flexing when the brakes are applied.
See attached image of a radial caliper and you can see the bolt holes that go down through the caliper body.