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The Mainframe OS Resource – Directory & Links
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The Mainframe OS section of Mainframes.in provides a listing of WWW resources for mainframe operating systems. Mainframes.in is a comprehensive online resource for legacy and mainframe systems.
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Content derived from Wikipedia article on Mainframe Computer
Mainframe computer From Wikipedia, the free encyclopedia
Mainframes (often colloquially referred to as Big Iron) are computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry/consumer statistics, ERP, and financial transaction processing.
The term originated during the early years of computing and referred to the large mechanical assembly that held the central processor and input/output complex. Later the term was used to distinguish high-end commercial machines from less powerful units which were often contained in smaller packages. Today, this term almost exclusively refers to IBM zSeries mainframes - descendants of the System/360.
Contents
1 Description 2 Characteristics 3 Market 4 History 5 Mainframes vs. supercomputers 6 Statistics 7 Speed and performance 8 See also 9 References 10 External links
Description Modern mainframe computers have abilities not so much defined by their performance capabilities as by their redundant internal engineering and resulting high reliability and security, and strict backward compatibility for older software. These machines often run for years without interruption, with repairs taking place during normal operation. They are also defined by high availability, one of the main reasons for their longevity, as they are used in applications where downtime would be catastrophic. The term Reliability, Availability and Serviceability (RAS) is a defining characteristic of mainframe computers.
Mainframes often support thousands of simultaneous users who gain access through specialized terminals or from smaller computers emulating terminals. Early mainframes either supported this timesharing mode or operated in batch mode where users had no direct access to the computing service; it solely provided back office functions. At that time mainframes were so called because of their very substantial size and requirements for specialized HVAC and electrical power. Nowadays mainframes support access via any user interface, including the Web. A mainframe was the first Web server anywhere outside Europe.[citation needed]
An IBM z890 mainframe Characteristics Nearly all mainframes have the ability to run (or "host") multiple operating systems and thereby operate not as a single computer but as a number of virtual machines. In this role, a single mainframe can replace dozens or even hundreds of smaller servers, reducing management and administrative costs while providing greatly improved scalability and reliability.
Mainframes can add system capacity nondisruptively and granularly. Modern mainframes, notably the IBM zSeries and System z9 servers, offer two levels of virtualization: logical partitions (LPARs, via the PR/SM facility), virtual machines (via the z/VM operating system), and have native hardware support for Linux and Java.
Mainframe return on investment (ROI), like any other computing platform, is dependent on its ability to scale, support mixed workloads, reduce labor costs, deliver uninterrupted service for critical business applications, and several other risk-adjusted cost factors. Some argue that the modern mainframe is not cost-effective. Sun Microsystems, Hewlett-Packard, and Dell understandably take that view, and so do some independent analysts. Hewlett-Packard also continues to manufacture its own mainframe, the NonStop system originally created by Tandem. Logical partitioning is now found in many high-end Unix-based servers. z9 servers execute each instruction twice, compare results, and shift workloads "in flight" to functioning processors, including spares, without any impact to applications or users. This feature, also found in HP's NonStop systems, is known as lock-stepping, because both processors take their "steps" (i.e. instructions) together. Not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processing.
Market As of early 2006, IBM mainframes dominate the mainframe market at well over 90% market share, however IBM is not the only vendor. Unisys manufactures ClearPath mainframes, based on earlier Sperry and Burroughs product lines, and a recent survey suggests its customers are loyal. Fujitsu's Nova systems are rebranded Unisys ES7000's. Hitachi co-developed the zSeries 800 with IBM to share expenses. Hewlett-Packard sells its unique NonStop systems, which it acquired with Tandem Computers, and Groupe Bull's DPS mainframes are available in Europe. Unisys and HP increasingly rely on commodity Intel CPUs rather than custom processors in order to reduce development expenses, while IBM typically develops new, homegrown technologies.
History Several manufacturers produced mainframe computers from the late 1950s through the 1970s. At this time they were known as "IBM and the Seven Dwarfs": Burroughs, Control Data, General Electric, Honeywell, NCR, RCA, and UNIVAC. IBM's dominance grew out of their 700/7000 series and, later, the development of the 360 series mainframes. The latter architecture has continued to evolve into their current zSeries/z9 mainframes which, along with the then Burroughs and now Unisys MCP-based mainframes, are among the few mainframe architectures still extant that dates from this early period. That said, while they can still run 24-bit System/360 code, the 64-bit zSeries and System z9 CMOS servers have almost nothing physically in common with the older systems. The larger of the latter IBM competitors were also often referred to as "The BUNCH" from their initials (Burroughs, UNIVAC, NCR, CDC, Honeywell). Notable manufacturers outside the USA were Siemens and Telefunken in Germany and ICL in the United Kingdom.
Shrinking demand and tough competition caused a shakeout in the market in the early 1980s — RCA sold out to UNIVAC and GE also left; Honeywell was bought out by Bull; UNIVAC (a division of Sperry) later merged with Burroughs to form Unisys Corporation in 1986. In 1991, AT&T briefly owned NCR. During the same period, companies found that servers based on microcomputer designs could be deployed at a fraction of the acquisition cost and offer local users much greater control over their own systems. Terminals used for interacting with mainframe systems were gradually replaced by personal computers. Consequently, demand plummeted and new mainframe installations were restricted mainly to financial services and government. In the early 1990s, there was a consensus among industry analysts that the mainframe was a dying market as mainframe platforms were increasingly replaced by personal computer networks.
That trend started to turn around in the late 1990s as corporations found new uses for their existing mainframes. The growth of e-business also dramatically increased the number of back-end transactions processed by mainframe software as well as the size and throughput of databases. Another factor currently increasing mainframe use is the development of the Linux operating system, which can run on many mainframe systems, typically in virtual machines. Linux allows users to take advantage of the open source software combined with mainframe hardware RAS.
Mainframes vs. supercomputers The distinction between supercomputers and mainframes is not a hard and fast one, but supercomputers generally focus on problems which are limited by calculation speed while mainframes focus on problems which are limited by input/output and reliability. The differences and similarities include:
Both types of systems offer parallel processing. Supercomputers typically expose it to the programmer in complex manners, while mainframes typically use it to run multiple tasks. One result of this difference is that adding processors to a mainframe often speeds up the entire workload transparently. Supercomputers are optimized for complicated computations that take place largely in memory, while mainframes are optimized for simple computations involving huge amounts of external data. Supercomputers are often purpose-built for one or a very few specific institutional tasks. Mainframes typically handle a wider variety of tasks. Consequently, most supercomputers are one-off designs, whereas mainframes typically form part of a manufacturer's standard model lineup. Mainframes tend to have numerous ancillary service processors assisting their main central processors (for cryptographic support, I/O handling, monitoring, memory handling, etc.) so that the actual "processor count" is much higher than would otherwise be obvious. Supercomputer design tends not to include as many service processors since they don't appreciably add to raw number-crunching power. There has been some blurring of the term "mainframe", with some PC and server vendors refer to their systems as "mainframes" or "mainframe-like". This is not widely accepted, and the market generally recognizes that mainframes are genuinely and demonstrably different.
Statistics 85% of all mainframe programs are written in the COBOL programming language 7% are written in Assembly language, C or C++ 5% are written in PL/I 3% are written in Java and other languages [citation needed]
Java use is increasing rapidly as of 2004, and these figures are likely significantly out-of-date, especially on newer mainframe systems. Also, mainframe COBOL has recently acquired numerous Web-oriented features, such as XML parsing, with PL/I following close behind.
90% of IBM's zSeries mainframes have its CICS transaction processing software installed.[1] Other software staples include the IMS, and DB2 databases, and MQSeries middleware. In the early 1990s the media and many business and computing analysts predicted the death of the mainframe. The predictions were disproved as many companies embraced the mainframe as offering an affordable means to handle their Internet business models. The quality of service offered by mainframes mean they are often the preferred technology for many business critical applications. As of 2004, IBM claimed over 200 new (21st century) mainframe customers — customers that had never previously owned a mainframe.
Speed and performance The CPU speed of mainframes has historically been measured in millions of instructions per second(MIPS). MIPS have been used as an easy comparative rating of the speed and capacity of mainframes. The smallest System z9 IBM mainframes today run at about 25 MIPS and the largest about 17,801 MIPS. IBM's Parallel Sysplex technology can join up to 32 of these systems, making them behave like a single, logical computing facility of as much as 221,248 MIPS .
The MIPS measurement has long been know to be misleading, and has often been parodied as "Meaningless Indicator of Processor Speed". The complex CPU architectures of modern mainframes have reduced the relevance of MIPS ratings to the actual number of instructions executed. Likewise, the modern "balanced performance" system designs focus both on CPU power and on I/O capacity . See benchmark (computing) for a brief discussion of the difficulties in benchmarking such systems. IBM has long published a set of LSPR (Large System Performance Reference) ratio tables for mainframes that take into account different types of workloads, and are a more representative measurement, however these comparisons are not available for non-IBM systems. It takes a fair amount of work (and maybe guesswork) for users to determine what type of workload they have and then apply only the LSPR values most relevant to them.
See also Supercomputer SUSE Linux Enterprise Server Red Hat Enterprise Linux
References ^ CICS-An Introduction. IBM. Retrieved on 2006-10-22.
External links IBM eServer zSeries mainframe servers Mainframe specifications Arcati Mainframe Yearbook Mainframe Made Easy Training Retrieved from http://en.wikipedia.org/wiki/Mainframe_computer
End of Wikipedia content, http://en.wikipedia.org/wiki/Mainframes
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