Tandem Computers, Inc. was the dominant manufacturer of fault-tolerant computer systems for ATM networks, banks, stock exchanges, telephone switching centers, 911 systems, and other similar commercial transaction processing applications requiring maximum uptime and no data loss. For example, in 2002, 95% of worldwide stock transactions and two-thirds of credit card transactions were handled by NonStop computers. The company was founded by Jimmy Treybig (CEO), Mike Green (VP Software), James Katzman (VP Engineering) and Jack Loustaunou (CFO) in 1974 in Cupertino, California. It remained independent until 1997, when it became a server division within Compaq. It is now a server division within Hewlett Packard Enterprise, following Hewlett-Packard's 2002 acquisition of Compaq and its 2015 split into HP Inc. and Hewlett Packard Enterprise. Tandem's NonStop systems use a number of independent identical processors, redundant storage devices, and redundant controllers to provide automatic high-speed "failover" in the case of a hardware or software failure. To contain the scope of failures and of corrupted data, these multi-computer systems have no shared central components, not even main memory. Conventional multi-computer systems all use shared memories and work directly on shared data objects. Instead, NonStop processors cooperate by exchanging messages across a reliable fabric, and software takes periodic snapshots for possible rollback of program memory state. Besides masking failures, this "shared-nothing" messaging system design also scales to the largest commercial workloads. Each doubling of the total number of processors doubles system throughput, up to the maximum configuration of 4000 processors. In contrast, the performance of conventional multiprocessor systems is limited by the speed of some shared memory, bus, or switch. Adding more than 4–8 processors in that manner gives no further system speedup. NonStop systems have more often been bought to meet scaling requirements than for extreme fault tolerance. They compete against IBM's largest mainframes, despite being built from simpler minicomputer technology.
Founding Tandem Computers was founded in 1974 by James Treybig who saw the market need for fault tolerance in online transaction processing systems while running a marketing team for Hewlett-Packard 's HP 3000 computer division but HP was not interested in developing for this niche. He then joined the venture capital firm Kleiner Perkins and developed the Tandem business plan there. Treybig pulled together a core engineering team hired away from the HP 3000 division. Their business plan called for systems that had no outages and never lost or corrupted data. These were modular in a way that was safe from all "single-point failures" yet would be only marginally more expensive than conventional non-fault-tolerant systems. They would be less expensive and support more throughput than some existing ad-hoc toughened systems that used redundant but usually required "hot spares". Each engineer was confident they could quickly deliver their own part of this complex design but doubted that others' areas could be worked out. The parts of the hardware and software design that did not have to be different were largely based on incremental improvements to the familiar hardware and software designs of the HP 3000. Many subsequent engineers and programmers also came from HP. Tandem headquarters in Cupertino, California, were a quarter mile away from the HP offices. Initial venture capital investment in Tandem Computers came from Tom Perkins, who was formerly a general manager of the HP 3000 division. The business plan included detailed ideas for building a unique corporate culture reflecting Treybig's values. The design of the initial Tandem/16 hardware was completed in 1975, and the first system shipped to Citibank in May 1976. The company enjoyed uninterrupted exponential growth through 1983. Inc. magazine ranked Tandem as the fastest-growing public company in America. By 1996, Tandem was a $2.3 billion company employing approximately 8,000 people worldwide.
Tandem NonStop (TNS) stack machines Over 40 years, Tandem's main NonStop product line grew and evolved in an upward-compatible way from the initial T/16 fault-tolerant system, with three major changes to its top-level modular architecture or its programming-level instruction set architecture. Within each series, there have been several major re-implementations as chip technology progressed. While conventional systems of the era, including large mainframes, had mean-time-between-failures (MTBF) on the order of a few days, the NonStop system was designed to failure intervals 100 times longer, with uptimes measured in years. Nevertheless, the NonStop was designed to be price-competitive with conventional systems, with a simple 2-CPU system priced at just over twice that of a competing single-processor mainframe, as opposed to four or more times of other fault-tolerant solutions.
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