The current methodology used in mass-market processor design is to create a single base microarchitecture (e.g., Intel’s “Core” or AMD’s “K8”) that is used throughout all of the PC market segments from laptops to servers. To differentiate the products, manufacturers rely on speed binning, different cache sizes, and varying the number of cores. In this paper, we propose using 3D integration to provide a new, but complementary, approach to providing product differentiation. Past research on using 3D to improve performance has focused on the construction of “fully 3D ” circuits where functional blocks are partitioned across two or more layers. This approach forces one of two undesirable situations: (1) all products must be implemented in, and therefore pay the cost of, 3D or (2) a 3D-implemented processor is designed for the high-end/high-performance markets and a separate 2D microarchitecture must be designed for the lower-cost markets thereby incurring significant additional design effort and engineering cost. We present a modular processor architecture where 3D can be used to enhance performance within a single unified design and also provides for a more gradual migration path toward fully 3D-integrated designs. To make this work, we describe a generic technique of using “phantom ” components where the baseline processor may believe that 3D-stacked resources exist, but are currently unavailable. Simply using 3D to stack more L2 cache provides a 15.1 % average performance benefit, but our proposal increases performance by 25.4%
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