1 Introduction

2 Hybrid Memory Architectures
2.1 Horizontal Hybrid Memory Architectures
2.2 Hierarchical Hybrid Memory Architectures
2.3 Architectures of Intel Optane DCPMM
2.4 Summary

3 Persistent Memory Management
3.1 Technical Challenges
3.2 Working Memory
3.3 Persistent Memory File System
3.4 Persistent Objects
3.5 Studies on Intel Optane DCPMMs

4 Performance Improvement and Energy Saving
4.1 NVMM Write Reduction
4.2 NVMM Energy Consumption Reduction
4.3 DRAM Energy Consumption Reduction

5 Write Endurance Improvement
5.1 Write Reduction
5.2 Wear-Leveling

6 Practices of Hybrid Memory System Designs
6.1 Memory Architectural Designs
6.2 System Software for Hybrid Memories
6.3 NVMM-supported Applications

7 Future Research Directions

8 Conclusions