High-speed source-synchronous interface for the IBM System z9 processor

As mainframes evolve and deliver higher performance, technologists are focusing less on processor speed and more on overall system performance to create optimized systems. One important area of focus for performance improvement involves chip-to-chip interconnects, with their associated bandwidths and latencies. IBM and related computer manufacturers are optimizing the characteristics of interconnects between processors as well as between processors and their supporting chip sets (local cache, memory, I/O bridge). This paper describes the IBM proprietary high-speed interface known as Elastic Interface (EI), which is used for nearly all chip-to-chip communication in the IBM System z9e. In particular, EI is a generic high-speed, source-synchronous interface used to transfer addresses, controls, and data between CPUs, L2 caches, memory subsystems, switches, and I/O hubs. The EI has single-ended data lines, resulting in twice the performance (bandwidth per pin) of similar buses operating with two differential lines per signal.