LRB & DX Raytracing are completely different beasts. LRB was a many-core device with some GPU features (the addsets, and fmaddXYZ instructions; texture-units at the turnstiles). DX Raytracing is a high level software API for driving specific classes of compute- and/or fragment- shaders onto plain-old GPUs. I believe the intention is to have dedicated Raytracing HW support in the future. I don't think dedicated HW is currently available.