ERD and Memory Architectures Paul Franzon Department of Electrical and Computer Engineering

2 High Level Overview Challenges for Memories  Power consumption  Bandwidth  Resiliency  Scaling (density, speed, power) Opportunities  Increased use of memory in logic and routing  Using ERD devices to help ERD memories scale  Intersection with 3DIC Impact on Memory Architectures  Scope for new and more specialized memory architectures  Mobile; (Cloud) Computing; SSD; Structured ASIC;

3 Challenge: Bandwidth  Soon to exceed 1 TBps  Key challenge: Power: DDR3 would consume 600 W at this bandwidth

4 Challenge: Power Consumption  Memory hierarchy is becoming the largest single consumer of the power in a computer  Consumes 30%+ of power in today’s servers  E.g. DARPA Exascale computing study Note: This assumed DRAM power was reduced from 600 pJ/bit to 3 pJ/bit

5 Challenge: Resiliency Issues:  SEU of SRAM  Checkpointing and resiliency of entire processor  Future scaled systems could spend 80% of their time checkpointing Note: DRAM Failures almost all due to packaging

6 Opportunity: Power  Reduced capacitance associated with scalable 4F 2 ERD memory technologies  Change RAM architecture  Smaller sub-arrays  Less energy/access  Low-swing interconnect  Reduced overhead  Revisit memory hierarchy to optimize energy, not latency  Exploit 3DIC for energy reduction

7 Challenge: Scaling Scaling  Peripheral Circuits  Smaller memory sub-arrays increases overhead of sense amps and row/column decoders  4F 2 cells increases overhead of sense amps and row/column decoders  Need:  Technologies and techniques to reduce overhead of peripheral circuits  Circuit Solutions  Use of ERDs  Use of 3DIC to implement peripheral circuits in a circuit- optimized technology

8 Challenge: Scaling 1R1D cells needed for resistive memories to ensure scalability (1R cells limits array size) Impact of rectification ratio on scalability with 1R1D cell On:Off Ratio Rectifcation  Memory Size

9 Opportunity: Memory as Logic 4F 2 programmable ERD memory cells permit high density Look Up Tables and programmable logic  Nanocrossbar  CMOL  Potential for high-speed (low C) and high density  Need to compare to logic ITRS to establish benchmark

10 Opportunity: Memory as Interconnect  Use programmable persistent memory elements as routable switchbox interconnect  Use high-density, low-overhead memory in NOC store/forward routing architectures  Example: Using a low-voltage nanocrystal flash device as an interconnect switch

11 Other Comments ERD as a Solid State Disk?  Definitely an opportunity but it looks like magnetic disk will always outscale solid state disk in density and cost/bit.  Instead use inside memory hierarchy, e.g. Disk cache, checkpoint store  ERD as Associative Memory, Bayesian inference calculator, etc.?  Some ERD have analog behaviors that have yet to be exploited or explored  E.g. Memristor, Memcapacitor, Meminductor

12 Other Comments Memory in Logic  3DIC and 4F 2 memory cells permits memory-heavy architectures to be revisited  But energy/bit-accessed has to better than energy/FLOP for computation  Real need are algorithms that increase spatial locality

13 Outline of ERD Chapter Memory Challenges  Table with metrics Solution paths to these challenges  Table with metrics New Opportunities for ERD  Architectural and circuit opportunities  Review of current memory enhanced architectures???  Nanocrossbar, CMOL, Synaptic  Tables, largely qualitative, somewhat quantitative

14 Feedback from Group 1.Quantify overhead of peripheral circuits as a function of core size 2.Latency matters too, both memory and interconnect. Typically traded for bandwidth. Quantify.