NonStop II

NonStop II. The NonStop II was a pioneering fault-tolerant computer system introduced by Tandem Computers in 1981, representing a significant evolution from its predecessor. It was designed for continuous operation in critical online transaction processing environments such as banking, telecommunications, and stock exchanges. The system's architecture emphasized hardware redundancy and sophisticated software to ensure data integrity and availability even during component failures.

Overview

The NonStop II solidified Tandem Computers' reputation as the leader in the fault-tolerant computing market during the early 1980s. It was deployed globally by major financial institutions like the New York Stock Exchange and service providers such as AT&T. The system's primary design goal was to eliminate any single point of failure, enabling it to support applications requiring extreme reliability and uptime. This made it a cornerstone technology for the burgeoning electronic funds transfer and automated teller machine networks of the era.

Architecture

The architecture of the system was based on a loosely coupled, shared-nothing architecture where independent processors communicated via a high-speed, dual-redundant inter-processor bus known as the Dynabus. Each processor module contained its own memory, I/O controllers, and power supply, ensuring that a failure in one module would not cascade. This modular design allowed for incremental scalability, enabling customers to expand processing power by simply adding more modules to the Dynabus. The physical packaging was designed for easy maintenance and hot swapping of components without shutting down the entire system.

Software and operating system

The system ran exclusively on the Guardian operating system, a message-based OS that managed process pairs across multiple processors. Key software components included TMF for managing database transactions and Enscribe as the primary database management system. Development tools like TAL and COBOL were supported, allowing programmers to build resilient applications for sectors like the SWIFT network and airline reservation systems. The software environment was integral to maintaining data consistency and facilitating automatic failover between redundant processes.

Hardware specifications

At its core, the NonStop II utilized a proprietary 16-bit custom microprocessor designed by Tandem Computers for enhanced error checking. Each processor cabinet could house multiple CPU and I/O modules, interconnected by the redundant Dynabus. Standard memory per processor module ranged up to 2 MB, which was substantial for commercial systems at the time. The system supported a wide array of peripherals, including disk drives from manufacturers like CDC and tape drives for backup. Its power supply units were also fully redundant, aligning with the overall philosophy of eliminating single point of failure.

Market reception and legacy

Upon release, the NonStop II was met with strong demand from the financial services industry and telecommunications companies, significantly boosting Tandem Computers' revenue and market share. It successfully competed against mainframe offerings from IBM and Digital Equipment Corporation in niche, mission-critical markets. The architectural principles established by the NonStop II directly influenced its successors, such as the NonStop VLX and the modern HP NonStop servers. Its legacy endures in contemporary high-availability computing and cloud infrastructure designs that prioritize fault tolerance and continuous availability.

Category:Fault-tolerant computer systems Category:Tandem Computers Category:1981 introductions