Dan´s Data has posted a review on the Hercules 3D Prophet 4500
The Kyro and Kyro II chipsets both sidestep the chief problem facing video chipset manufacturers - memory bandwidth. Complex 3D scenes with thousands of polygons in them require a lot of memory activity to render each frame. The more polygons you´re rendering, the faster the video memory needs to be, for a given final frame rate.Read more
When a 3D card draws you a view of a 3D world, it has, classically, to render every single thing in that world. The most obvious way to do this is to simply render every single polygon that faces the viewer, from most distant to closest, in that order. That way, closer things will occlude more distant things, as they´re supposed to, and you´ll end up with a perfectly all right image.