Abstract: We present a system architecture for the 4^th generation of PC-class programmable graphics processing units (GPUs). The new pipeline features significant additions and changes to the prior generation pipeline including a new programmable stage capable of generating additional primitives and streaming primitive data to memory, an expanded, common feature set for all of the programmable stages, generalizations to vertex and image memory resources, and new storage formats. We also describe structural modifications to the API, runtime, and shading language to complement the new pipeline. We motivate the design with descriptions of frequently encountered obstacles in current systems. Throughout the paper we present rationale behind prominent design choices and alternatives that were ultimately rejected, drawing on insights collected during a multi-year collaboration with application developers and hardware designers.