Tandem Computers was an early manufacturer of fault tolerant computer systems, marketed to the growing number of transaction processing customers who used them for ATMs, banks, stock exchanges and other similar needs. Tandem systems used a number of redundant processors and storage devices to provide high-speed "failover" in the case of a hardware failure, an architecture that they called NonStop. Over the two decades from the 1970s into the mid-90s, Tandem systems evolved from custom hardware to commodity CPU designs. The company was eventually purchased by Compaq in 1997 in order to provide that company with more robust server offerings. Today it is still known as NonStop, as a separate product line offered by Hewlett-Packard. Fault-tolerance or graceful degradation is the property of a system that continues operating properly in the event of failure of some of its parts. ... A BlueGene supercomputer cabinet. ... In computer science, transaction processing is information processing that is divided into individual, indivisible operations, called Each transaction must succeed or fail as a complete unit; it cannot remain in an intermediate state. ... Outdoor ATMs may be free-standing, like this kiosk, or built into the side of banks or other buildings An automatic teller machine, automated teller machine (ATM) or cash machine is an electronic device that allows a banks customers to make cash withdrawals and check their account balances without... BRD-SG in IaÅŸi - A small branch dedicated to retail services For other uses, see Bank (disambiguation). ... Failover is the capability to switch over automatically to a redundant or standby computer server, system, or network upon the failure or abnormal termination of the previously active server, system, or network. ... Compaq Computer Corporation is an American personal computer company founded in 1982, and now a brand name of Hewlett-Packard. ... This article or section does not cite its references or sources. ... The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ...

History

Tandem Computers was founded in 1974 by a group of engineers from Hewlett-Packard, led by James Treybig. Their business plan called for systems that were safe from "single-point failures" that were only slightly more expensive than competing non-fault tolerant systems. Tandem considered this to be very important to their business model. Limiting the additional expense was important since customers often developed procedural solutions to failures when the price of fault tolerant hardware was too high. The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... James (Jim) Treybig founded Tandem Computers, a pioneering Silicon Valley manufacturer of fault tolerant computer systems which were marketed to the growing number of transaction processing customers who used them for ATMs, banks, stock exchanges and other similar needs. ... Reliable system design is the design of systems with high levels of reliability and availability. ... Fault-tolerance or graceful degradation is the property of a system that continues operating properly in the event of failure of some of its parts. ...

The first system was the Tandem/16 or T/16 (later renamed NonStop I after the introduction of its successor, the NonStop II). The system design was complete in 1975, and the first example was sold to Citibank in 1976. The machine consisted of between 2 and 16 processors, each capable of about 0.7 MIPS with their own memory, I/O buses, and dual connections to their custom inter-CPU computer bus, Dynabus. The modules were constructed with dual paths so that any single failure would always leave at least one bus (both I/O and Dynabus), free for use by the other modules. The CPU was influenced by the HP3000 CPU, a microprogrammed 16-bit stack-based machine with 16-bit user addressing. Like the HP3000, the NonStop CPU added a number of registers for fast access, such as base addresses for global and local variables. Citibank is a major international bank, founded in 1812 as the City Bank of New York. ... MIPS may mean: MIPS architecture, a RISC microprocessor architecture. ... This article is about the computer interface. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ... The Hewlett-Packard 3000 series is a family of minicomputers released by the company in 1973 after a difficult development project. ... A microprogram is a program consisting of microcode that controls the different parts of a computers central processing unit (CPU). ... In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... In computer science, a stack machine is a model of computation in which the computers memory takes the form of a stack. ... In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a given point in time. ...

The Tandem NonStop series ran a custom operating system, initially called T/TOS (Tandem Operating System), later Guardian, and finally NonStop Kernel. It supported a "NonStop" programming paradigm that allowed a program to be completely fault tolerant. Several other companies introduced failover technologies but only Guardian supported completely fail-safe transaction processing. A properly constructed Guardian program could restart from any point and resume transaction processing without any loss of data. An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ...

While conventional systems of the era, including mainframes, had failure rates on the order of a few days, the NonStop system was designed to fail 100 times less, with "uptimes" measured in years. Nevertheless the NonStop was deliberately designed to be price-competitive with conventional systems, with a simple 2-CPU system priced at just over two times that of a competing single-processor mainframe, as opposed to four or more times of most competing solutions. This article or section does not adequately cite its references or sources. ...

NonStop I was followed by the NonStop II in 1981, a slight improvement in speed to 0.8 MIPS, but a more measurable upgrade in memory from a maximum of 1 MB per CPU in the later versions of the NonStop I, to 2 MB in the II, and the addition of a revamped virtual memory system allowing for considerably larger address spaces. The NonStop I was limited to 4 virtual memory segments (System Data, System Code, User Data, User Code) each limited to 128 kB in size. The NonStop II increased the number of memory maps from 4 to 16, 8 of which were used for I/O, and provided a 32 bit address mode with user-accessible "extended segments" virtually unlimited in size. The same basic system, including the physical packaging, was used in 1983's NonStop TXP system that over doubled the speed to 2.0 MIPS, and the physical memory to 8 MB. In all of these machines the same Dynabus system was used, which had been overdesigned in the NonStop I so they could avoid changing it in the future. Virtual memory is an addressing scheme implemented in hardware and software that allows non-contiguous memory to be addressed as if it is contiguous. ...

Introduced along with the TXP was a new fibre optic bus system, FOX. FOX allowed a number of TXP and NonStop II systems to be connected together to form a larger system with up to 14 nodes. Like the CPU modules within the computers, Guardian could failover entire task sets to other machines in the network. Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ...

The company attempted to grab a piece of the rapidly-growing personal computer market in 1985 with its introduction of the MS-DOS based Dynamite PC/workstation. Sadly, numerous design compromises (include a unique 8086-based hardware platform incompatible with expansion cards of the day and extremely limited compatibility with IBM-based PC's) relegated the Dynamite to serving primarily as a smart terminal. It was quietly withdrawn from the market within a short period of time. Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... International Business Machines Corporation (known as IBM or Big Blue; NYSE: IBM) is a multinational computer technology corporation headquartered in Armonk, New York, USA. The company is one of the few information technology companies with a continuous history dating back to the 19th century. ...

In 1986 a major upgrade to the system was introduced, the NonStop VLX. VLX used a new Dynabus, increasing speed from 13 Mbit/s to 40 Mbit/s (total, 20 Mbit/s per independent bus). They also introduced FOX II, increasing the size of the networks from 1 km to 4 km. Using the original FOX VLX systems could be used with the older NonStop II and TPX's, but these systems were not supported on FOX II.

VLX was partnered with the NonStop CLX, a minicomputer sized machine for smaller installations. The CLX had roughly the same performance as the earlier TXP, but was much smaller and less expensive. By the end of its lifetime the CLX had increased in speed considerably, and competed with the VLX, 1991's CLX 800 was only about 20% slower than the VLX, with the main difference being more limited expansion abilities. Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). ...

In 1986 Tandem also introduced the first fault-tolerant SQL database, NonStop SQL. Developed totally in-house, NonStop SQL included a number of features based on Guardian to ensure data validity across nodes. NonStop SQL was famous for scaling linearly in performance with the number of nodes added to the system, whereas most databases of the era had performance that plateaued quite quickly, often after two CPUs. A later version released in 1989 added transactions that could be spread over nodes, a feature that remained unique for some time. Later, the SQL database group was first co-opted then absorbed into Microsoft's SQL development effort. One outcome of this collaboration was Microsoft's clustered system technology. Structured Query Language (SQL) is the most popular computer language used to create, retrieve, update and delete data from relational database management systems. ... NonStop SQL is a relational database product originally produced at Tandem Computers using the pioneering Ingres source code from University of California, Berkeley. ... In computer science, in a distributed system such as a distributed shared memory system or a distributed data store such as a database, filesystem, or web caching system, there are a number of possible data consistency models. ... It has been suggested that this article or section be merged with Scale (computing). ... In parallel computing, speedup refers to how much a parallel algorithm is faster than a corresponding sequential algorithm. ...

The NonStop Cyclone was introduced in 1989, introducing a new superscalar CPU design. It was otherwise similar to earlier systems, although much faster. In general terms the Cyclone was about four times as fast as the CLX 800, which Tandem used as their benchmark. On the downside the new CPU was complex and expensive, requiring four circuit boards to implement a single CPU. Simple superscalar pipeline. ...

In 1991 Tandem followed this with RISC-implementations of Guardian, running on MIPS R3000-based CPU modules in the Cyclone/R and CLX/R. Programs written for the earlier stack-based CPU design were automatically translated on the fly into R3000 code in an interpreter, although they ran considerably slower than on earlier machines. Tandem also provided a number of tools to easily port existing object code to the new systems, resulting in code that was some 25% slower than the original Cyclone. Source code compilers were also available. While slower, the new system was considerably less expensive, and it was clear that RISC performance was outpacing CISC. By making the move when they did, they were banking on increases in MIPS performance quickly wiping out any performance disadvantages the system had at the time. In 1993 the NonStop Himalaya K-Series using the MIPS R4400 was shipped. Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ... A MIPS R4400 microprocessor made by Toshiba. ... An interpreter is a computer program that executes other programs. ... In computer science, object file or object code is an intermediate representation of code generated by a compiler after it processes a source code file. ... Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. ...

In 1997 Tandem introduced the NonStop Himalaya S-Series. The S-Series machines were the first systems that changed the underlying architecture of the NonStop family, basing both the I/O and inter-CPU communication on their new ServerNet interconnect. Whereas Dynabus and FOX linked the CPU's together into a ring network, ServerNet was a true point-to-point network replacing both, and ran at much higher speeds. ServerNet later was used as the basis of the InfiniBand industry standard. The S-Series machines continued the use of MIPS processors, including the R4400 and R10000. Ring network layout A ring network is a topology of computer networks where each node is connected to two other nodes, so as to create a ring. ... InfiniBand is a switched fabric communications link primarily used in high-performance computing. ...

All the more recent systems were based on microprocessors, and the internal circuits of these chips are not fully checked. To assure correct computation, each logical processor had two microprocessors operating in lockstep. If the results coming out ever disagreed, the processor was considered to be faulting and instantly stopped. At that point Guardian would move that task to another processor as in earlier systems, guaranteeing that bad data was never written out due to hardware failures. This article or section does not adequately cite its references or sources. ...

A different approach was used in a separate family of computers, the Integrity line. These computers used additional redundant CPUs running the same instruction stream. When a fault was detected (e.g. by lockstep mismatch), the failing module was disabled but the redundant module continued processing the instruction stream without interruption. Since this was handled primarily in hardware, it could be used with a slightly modified conventional operating system; Integrity used a Unix variant rather than Guardian. The line was introduced in 1989, apparently as a response to the machines of Stratus Technologies (which were remarketed by IBM as System/88). Although distinct from the NonStop line, the Integrity designs were also based on the MIPS processors. With the introduction of the Integrity S4000 in 1995, the line was the first to use ServerNet and moved towards sharing hardware designs with the NonStop line. Stratus Technologies is a Maynard, Massachusetts based producer of fault tolerant computers. ... IBM fault tolerant minicomputer based on Stratus Technologies -- basically a Stratus system with an IBM badge on it. ...

Tandem was acquired by Compaq in 1997. Compaq was in turn acquired by HP in 2002, bringing Tandem back to its original roots. As of 2003, the NonStop product line continues to be produced, under the HP name. Compaq Computer Corporation is an American personal computer company founded in 1982, and now a brand name of Hewlett-Packard. ... 1997 (MCMXCVII) was a common year starting on Wednesday of the Gregorian calendar. ...

After being acquired by HP, the NonStop line has moved to Itanium based processors, called Integrity NonStop Servers. The original Integrity line is no longer produced but the name 'Integrity' has been adopted by HP for all Itanium based servers. Itanium 2 logo Old Itanium logo The Itanium is an IA-64 microprocessor developed jointly by Hewlett-Packard and Intel. ...

The NonStop Kernel (NSK) can run multiple OS's. In addition to the Guardian OS, the modern NonStop platform incorporates a POSIX compatible environment (OSS) and Java. There is also an effort by HP to run Linux on the NonStop hardware.^[1] Also, Linux or other Unix based operating systems could be installed on the NonStop platform via a virtual machine environment. POSIX or Portable Operating System Interface[1] is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API) for software compatible with variants of the Unix operating system. ... Java refers to a number of computer software products and specifications from Sun Microsystems (the Java™ technology) that together provide a system for developing and deploying cross-platform applications. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system family. ... Linux (IPA pronunciation: ) is a Unix-like computer operating system family. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®) is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... In computer science, a virtual machine is software that creates a virtualized environment between the computer platform and its operating system, so that the end user can operate software on an abstract machine. ...

Culture

Tandem treated its employees with a great deal of respect, especially in the years leading to the company's first billion-dollar yearly sales figure. Innovative programs included:

• TOPS ("Tandem Outstanding PerformerS") - every employee in the company could be nominated for this award, which was awarded to about the top 5% of employees annually. Winners (and a guest of their choosing) were treated to an all-expense paid trip to locations such as Hawaii, Vail, and similar resort areas for several days of fun and teambuilding. Management actually worked the event as hosts. TOPS was known, among other things, for its 24-hour open bar, where one could encounter senior VPs and even the company CEO dishing out drinks and stories of the company's early years.
• Annual stock option - every employee of the company received a 100-share stock option each fall. As the company's stock rose (or split), employees could share in the company's financial success.
• Sabbaticals - all US employees earned a six-week paid sabbatical (contiguous vacation) every four years, which could be augmented with personal vacation. Employees who chose to perform public service during their sabbatical could apply for an additional three weeks.
• "First Friday" - the award-winning in-house Tandem TV staff produced a monthly program, broadcast live to all Tandem locations world-wide. While generally educational about some aspect of the company, the programs usually featured some member of the senior management team in a humorous way.
• "Beer Bust" - Tandem sponsored a weekly get-together for its employees world-wide. It was called "beer bust" due to the availability of beer and wine, paid for by the company, in addition to other beverages and prepared food. This gave employees a way to cross barriers. It was not uncommon to see employees from various functions huddled in a corner, beer in hand, working to solve a problem.
• "Third Class Mail" - Tandem was one of the first companies in which every employee had access to e-mail, which was divided into first, second, and third classes. Third Class mail allowed employees to buy and sell goods, ask questions, and share information that was not company-related. A wide variety of "SIGs" (Special Interest Groups) allowed employees to share a variety of interests with each other.

As the company entered the 90's, however, sales and profits slowed, and many of these innovative programs were either curtailed or eliminated totally. By the end, Tandem was pretty much a company like any other in the computer field, culminating in the buyout by Compaq, who wasted little time eliminating almost all of these. Only beer bust, in a greatly watered down form (literally - many sites banned alcohol), survived.

References

External links

• NonStop Computing Home - the main Nonstop Computing page at HP
• Tandem Technical Reports - a page at HP with a number of Tandem white papers
• Tandem Systems Review PDFs 1983-1994