Utilizing Radio-Frequency Interconnect for a Many-DIMM DRAM System

Abstract

The demand for capacity and off-chip bandwidth to dynamic random-access memory (DRAM) will continue to grow as we integrate more cores onto a die. However, as the data rate of DRAM has increased, the number of dual in-line memory modules (DIMMs) supported on a multi-drop bus has decreased. Therefore, traditional memory systems are not sufficient to meet both these demands. We propose the DIMM tree architecture for better scalability by connecting the DIMMs as a tree. The DIMM tree architecture is able to grow the number of DIMMs exponentially with each level of latency in the tree. We also propose application of multiband radio-frequency interconnect (MRF-I) to the DIMM tree architecture for even greater scalability and higher throughput. The DIMM tree architecture without MRF-I was able to scale up to 64 DIMMs with only an 8% degradation in throughput over an ideal system. The DIMM tree architecture with MRF-I was able to increase throughput by 68% (up to 200%) on a 64-DIMM system over a 4-DIMM system. Finally, we propose the partitioned DIMM tree, which allows the scaling of a main memory system to a many-DIMM memory system while still maintaining high throughput. The partitioned DIMM tree is able to improve throughput by an average of 19% up to 35% over the DIMM tree with 256 DIMMs on a single channel.