The Scalable Coherent Interface (SCI) is an ANSI/IEEE standard that defines an extremely flexible high speed, point-to-point packet link protocol. Although the original intent of SCI was a new, faster one Gbit/sec backplane, it’s framers looked well beyond that, implanting within it a superior scalable transport medium, low latency, and memory cache coherency. SCI is designed to enable highly-efficient data communications and memory sharing between processors, system boards, or chassis backplanes.

The IEEE standardization work on SCI started in 1989 and, when finalized in 1992, implementation got a slow start, except for a team in Norsk Data that followed the IEEE group and implemented SCI while it was defined. This team ultimately formed the company now known as Dolphin Interconnect. With their long experience in this unique technology and work with numerous industry partners over the following years the technology is now highly refined and delivering on its original vision and more.

SCI is not a LAN, but rather a multiprocessing area network technology. As such, SCI is a leading technology for building scalable multiprocessor systems, since it avoids the bottlenecks that occur with traditional bus and networking-based technologies. SCI is commonly used today for server clustering by companies like Sun Microsystems, as well as for multiprocessing in military and aerospace applications. SCI is also extensively deployed in massively-parallel processing applications at many of the world’s most advanced research facilities.

Flexibility–SCI can be implemented as a 16-bit parallel link using ring or switched-star topologies, depending on performance requirements. Low Latency–parallel SCI links provide low-latency interconnections between boards and/or systems using standard backplane interfaces such as VME, PCI, or CPCI, and even using mezzanine configurations. Data Delivery–another inherent characteristic of the SCI protocol is “guaranteed data delivery,” providing an extremely robust and reliable solution.

Today, SCI-based products are available that provide simultaneous transmit and receive links with speeds of 667 Mbytes/sec, or 5.33 Gbits/sec, with a node-to-node message latency of less than 1.4 micro seconds. Further, SCI-based products will reach Bidirectional link speed is 1.333 GBytes/s and ring capacity for random traffic is 1 GByte/s.

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