Research And Implementation Of A Simulation System For PCM/DRAM-Based Hybrid Memory

Phase change memory(PCM)has emerged as a new kind of memory with attractive features,such as non-volatility,fast read speed,high density,and low power consumption.These properties make PCM be a candidate of future memories that aim to replace existing memories like DRAM.However,PCM has a low write-speed and limited write-endurance,which makes it unpractical to completely replace DRAM with PCM at this moment.This also opens several research problems,i.e.,how to use PCM at memory hierarchy,how to take advantages of PCM and DRAM in order to achieve fast response,large capacity,high reliability in future memory systems,how to innovate data management on hybrid memory,etc.However,so far PCM chips are still on the research stage and PCM-based storage devices are not available.This makes it hard to carry out researches upon real PCM devices as well as on PCM-related memory systems.As a result,the lack of PCM-related test bed will hinder the advance of algorithmic studies.Further,even if PCM devices will be available in the future,we still need a simulation tool to provide different configuration options of memory hierarchy,so that we can devise algorithms towards specific memory hierarchy.Therefore,in order to solve the contradiction between numerous PCM related research and the lack of experimental environment,the main research work of this paper is to design and construct a simulation system for DRAM/PCM-based hybrid memory,which provides high configurability,simple operations,and accurate results.Firstly,this thesis outlines the background and significance of the research,introduces the characteristics of the existing memory simulators.Meanwhile,we point out that those simulators cannot fully meet the actual needs of current PCM-based research.And thus,we propose a simulator system called DPHSim for evaluating DRAM/PCM-based hybrid memory systems.In this paper,we are devoted into the implementation of the simulation system architecture,functional modules,timing model,power model,hybrid memory allocation interfaces and graphical user interfaces.At the end of the paper,the validity and availability of the simulator are illustrated by the verification experiments and study cases.The contributions of this paper are summarized as follows:(1)A simulation system is designed and implemented,which supports several various kinds of memory hierarchy,including DRAM-only,PCM-only,PCM as the cache of DRAM,and hybrid memory(PCM and DRAM are both used as main memory).(2)The timing model and the power model built in the simulation system realize the effective and accurate duration and energy evaluations on the memory systems with different configurations.(3)A user-controlled hybrid memory allocation interface is proposed,which makes up the disadvantage that the existing simulators cannot expose the hybrid storage space to programmers.(4)Several application scenarios of the simulation system are provided,which show the practical convenience for the PCM-based research.