Aquarianna:Hilary- I don't quite understand what you mean by using a backplate...don't all bc's have one? Or maybe I'm just more confused than I know
I'm sorry, when I said BP/W I just assumed you knew that was common abbreviation for BackPlate & Wings.
This is different from a BC backing. A traditional BC may have a hard or soft pack but it's all one single piece of equipment. A BP/W is a component setup where each component can be selected and replaced separately. The backplate itself is just a piece of metal with holes and slots drilled into it. The harness is webbing that threads through the slots and holds the backplate onto your back. The wings are the buoyance bladder that bolt onto the backplate. Also attached to the backplate are the cam straps for single tank or cam bands for doubles.
See this site for some pictures. The advantages of BP/W is that the buoyancy is on your back, your arms move more freely, you lose the weight belt or much of the weight in it, and you have firmer tank support. Backplates can be aluminum or stainless steel. Some people have both, switching out the plate depending on type of dive. Some people have two wings, one for single tank and one for doubles. You can create many configurations by changing out components.