Mahendra R. Patel,
Corporate Consulting Engineer,
Vice President, Systems Engineering

Systems engineering is the engineering of complete systems as opposed to parts of systems. Exactly what this means depends on one's point of view. One person's system is another person's component. From chips to boards to boxes to clusters to networks, subsystems are combined into ever larger and more complex aggregates. At Digital, systems engineering means the engineering of systems at a level of aggregation above individual hardware or software products. Individual processors, storage subsystems, network hubs, operating systems, database systems, and applications are viewed as components of the system. For example, a nationwide network for interactive securities trading, built from hundreds of nodes at dozens of sites, is one system.

A number of trends in the computer industry make it more challenging for a computer company to practice systems engineering:

• Commoditization: Component products, from microprocessors to applications, are increasingly becoming low-cost, high-volume commodities. Ironically, as the cost of the components drops, the cost of integrating them into complete systems becomes a larger fraction of total system cost.
• Distributed systems: While they provide new opportunities for better performance, scaling, and fault-tolerance, distributed systems also present new engineering challenges for ensuring these same attributes.
• Heterogeneous systems: Increasingly, computers from a variety of vendors, running a variety of operating systems, are being connected together and are expected to work together correctly.
• Complexity: Distributed systems are becoming more complex for a number of reasons. The number of components is growing. The number of types of components that must work together is growing. And the variety of unique configurations is growing.

Over the last decade, the computer industry has changed from one that offered vertically integrated systems built from proprietary CPUs, disks, networks, operating systems, and layered products to one that produces commodity products conforming to de jure or de facto standards. Unlike the manufacture of automobiles or aircraft, a single computer manufacturer seldom produces all the components of a complete working system. The hardware, system software, and applications often come from three different vendors. Systems engineering, as now practiced in the computer industry, places less emphasis on top-down design of hardware and software components and their interfaces to meet system-level goals. Rather, it is based on anticipating a broad spectrum of system designs.

From the point of view of a computer company, systems engineering must now be concerned with assemblies of commodity hardware and software products. Thus, four areas are of special interest to systems engineering in the computer industry: interoperability, performance, scalability, and availability.

Interoperability of components, including components from different vendors, is difficult to verify because of the virtually infinite number of possible combinations of components. For example, the introduction of a new component often can expose bugs in system components previously thought to be working. Systems engineering work in this area includes the development of tools for effective testing and the development of industry standards for interoperability.

The performance of a system can depend in a complicated way on the performance of its components. Sophisticated tools are needed to predict the performance of a complex system from the performance of its parts, or to diagnose subtle interactions between components that affect performance. Today, performance tools for distributed systems are not as sophisticated as those for individual computers.

Scalability refers to the ability of a system to start small and grow big. Size may be measured in terms of numbers of users, computers, disks, applications, or a combination of parameters. The ability to scale up distributed systems over two orders of magnitude by adding components is one of their most attractive attributes. However, scaling effectively requires careful analysis and design of the system. For example, a system design based on cost-effective packaging of functionality at a small scale can exhibit bottlenecks as computers are added to the system to handle increased workloads.

A distributed system is inherently less reliable unless care is taken to improve availability by adding redundant components. Simply partitioning functionality between a client and server computer requires that both the client and the server be working for the functionality to be available. Given technology with the same failure and repair characteristics, distributing functionality between two computers results in a system that is less available than one with the complete functionality on one computer. Often this is an academic point in simple systems, given the levels of component reliability. However, distributed systems with critical availability requirements (e.g., a nationwide network for interactive securities trading) demand careful analysis and design to add appropriate redundancy.

Systems engineering is important to Digital because even the best component products are of no value to customers until they are integrated into complete working systems that meet business needs. Ideally, one would like to be able to build large, complex systems by simply snapping together small, simple components, as if they were Lego blocks. It is tempting to assume that this should be easy because many of the components are available as inexpensive, mass-produced, reliable commodities. However, building complex systems from simple parts is still difficult and requires engineering work, especially when the overall system stretches the limits of the technology.

Systems engineers play a vital role in major systems integration projects that push the edge of the technology envelope in some way. The system may combine components that have never before been used together. The trend toward more heterogeneous systems makes this more likely. The system may stretch scaling limits by having more nodes or network connections or users or data than ever before. The trend toward large distributed systems makes this scaling possible. The system may need to meet very demanding requirements for overall system performance or dependability. Increasingly, heterogeneous, distributed systems are being used for mission-critical business applications.

Engineering analysis and design is needed at all phases of a complex integration project, from the definition of the technical requirements to the design of the system to final testing and verification. Custom software or hardware may need to be developed, either to glue together components that were not built to work together or to substitute for standard components in order to meet demanding requirements for performance or scaling.

Systems engineers also develop tools and methods to simplify the task of integrating complete systems. Digital's systems engineers are active in the development of industry standards for ensuring the interoperability of components from different vendors. In this issue of the Journal, Eric Newcomer's paper describes the development of standards for use in the telecommunications industry. Often, a system has legacy components. Digital's systems engineers are also active in the development of frameworks that apply object-oriented programming technologies to encapsulate legacy applications and data, simplifying the incorporation of legacy components into new systems. A framework for the integration of manufacturing applications is described in the paper by James Kirkley and William Nichols. The Systems Engineering group has developed a variety of test tools and methods, and operates an extensive laboratory for testing, verification, and performance characterization of combinations of products from Digital and other vendors. Technical data from testing and characterization is the basis for configuration guidelines for systems intended to run a number of popular commercial applications.

Computers, disks, network switches, database systems, desktop applications, and many other components are now available as inexpensive, reliable commodities. Hardware and software components from various manufacturers can be put together to build a wide variety of systems, from one as simple as a PC to one as complex as a worldwide distributed system.

While the cost of the components has dropped dramatically in recent years, the cost of integrating these simple components into complex distributed systems remains high and therefore represents a larger fraction of the total cost of the system. Today, Digital's ability to successfully build complex distributed systems provides great value for our customers, often greater than the value of the commodity components from which the systems are built. For the future, improvements in tools and methods for building complex systems will lower the cost of these systems significantly, making new types of applications feasible and affordable.

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