SHF: Small: Architecting the COSMOS:A Combined System of Optical Phase Change Memory and Optical Links

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Today’s data-intensive applications that use graph processing, machine learning or privacy-preserving paradigms demand memory sizes on the order of hundreds of GigaBytes and bandwidths on the order of TeraBytes per second. To support the ever-growing memory needs of the applications, Dynamic Random Access Memory (DRAM) systems have evolved over the decades. However, DRAM will not be able to support these large-capacity and -bandwidth demands in the future in an efficient and scalable way. While there is research on a number of alternate memory technologies (such as phase-change memory, magnetic memory, resistive memory, etc.), there is no clear winner among these technologies to replace DRAM. Moreover, none of these alternate memory technologies nor DRAM efficiently complements the silicon-photonic link technology that is expected to replace high-speed electrical links for processor-to-memory communication in the near future. This project aims to address the problems arising from limited memory capacity and bandwidth, which are significant limiting factors in application performance, through a unified network and memory system called COSMOS. COSMOS integrates Optically-controlled Phase Change Memory (OPCM) technology and silicon-photonic link technology to achieve a "one-stop-shop" solution that provides seamless high-bandwidth access from the processor to a high-density memory. The project goes beyond solely using OPCM as a DRAM replacement, and aims to demonstrate the true potential of OPCM as non-volatile memory and in processing-in-memory (PIM) design scenarios. At a broader level, the project seeks to improve the performance of many societal data-driven applications in various domains, including healthcare, scientific computing, transportation, and finance.The research goals of this project are to design the first full system architecture for COSMOS, and then demonstrate its benefits using realistic application kernels, when OPCM is used as a DRAM replacement, in an OPCM+DRAM combination with persistence properties, and in OPCM as PIM scenarios. To achieve these ambitious goals, the project is organized into the following three research thrusts and a cross-cutting thrust. Thrust 1 designs a full-system architecture using OPCM and silicon-photonic links to address the memory capacity and bandwidth requirements of data-centric applications. Thrust 2 investigates the use of COSMOS for PIM, where the stored data is processed at the speed of light. Thrust 3 aims to create mechanisms and methods for application developers and the Operating System to profile and instrument applications for making effective use of COSMOS. The Cross-cutting Thrust builds a simulation methodology to accurately evaluate the benefits of OPCM as DRAM replacement as well as for combined OPCM+DRAM and OPCM as PIM designs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.