WIKIBOOKS
DISPONIBILI
?????????

ART
- Great Painters
BUSINESS&LAW
- Accounting
- Fundamentals of Law
- Marketing
- Shorthand
CARS
- Concept Cars
GAMES&SPORT
- Videogames
- The World of Sports

COMPUTER TECHNOLOGY
- Blogs
- Free Software
- Google
- My Computer

- PHP Language and Applications
- Wikipedia
- Windows Vista

EDUCATION
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LITERATURE
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LINGUISTICS
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- English Dictionaries
- The English Language

MEDICINE
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- The Theory of Memory
MUSIC&DANCE
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SCIENCE
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- Nanotechnology
LIFESTYLE
- Cosmetics
- Diets
- Vegetarianism and Veganism
TRADITIONS
- Christmas Traditions
NATURE
- Animals

- Fruits And Vegetables



ARTICLES IN THE BOOK

  1. Adobe Reader
  2. Adware
  3. Altavista
  4. AOL
  5. Apple Macintosh
  6. Application software
  7. Arrow key
  8. Artificial Intelligence
  9. ASCII
  10. Assembly language
  11. Automatic translation
  12. Avatar
  13. Babylon
  14. Bandwidth
  15. Bit
  16. BitTorrent
  17. Black hat
  18. Blog
  19. Bluetooth
  20. Bulletin board system
  21. Byte
  22. Cache memory
  23. Celeron
  24. Central processing unit
  25. Chat room
  26. Client
  27. Command line interface
  28. Compiler
  29. Computer
  30. Computer bus
  31. Computer card
  32. Computer display
  33. Computer file
  34. Computer games
  35. Computer graphics
  36. Computer hardware
  37. Computer keyboard
  38. Computer networking
  39. Computer printer
  40. Computer program
  41. Computer programmer
  42. Computer science
  43. Computer security
  44. Computer software
  45. Computer storage
  46. Computer system
  47. Computer terminal
  48. Computer virus
  49. Computing
  50. Conference call
  51. Context menu
  52. Creative commons
  53. Creative Commons License
  54. Creative Technology
  55. Cursor
  56. Data
  57. Database
  58. Data storage device
  59. Debuggers
  60. Demo
  61. Desktop computer
  62. Digital divide
  63. Discussion groups
  64. DNS server
  65. Domain name
  66. DOS
  67. Download
  68. Download manager
  69. DVD-ROM
  70. DVD-RW
  71. E-mail
  72. E-mail spam
  73. File Transfer Protocol
  74. Firewall
  75. Firmware
  76. Flash memory
  77. Floppy disk drive
  78. GNU
  79. GNU General Public License
  80. GNU Project
  81. Google
  82. Google AdWords
  83. Google bomb
  84. Graphics
  85. Graphics card
  86. Hacker
  87. Hacker culture
  88. Hard disk
  89. High-level programming language
  90. Home computer
  91. HTML
  92. Hyperlink
  93. IBM
  94. Image processing
  95. Image scanner
  96. Instant messaging
  97. Instruction
  98. Intel
  99. Intel Core 2
  100. Interface
  101. Internet
  102. Internet bot
  103. Internet Explorer
  104. Internet protocols
  105. Internet service provider
  106. Interoperability
  107. IP addresses
  108. IPod
  109. Joystick
  110. JPEG
  111. Keyword
  112. Laptop computer
  113. Linux
  114. Linux kernel
  115. Liquid crystal display
  116. List of file formats
  117. List of Google products
  118. Local area network
  119. Logitech
  120. Machine language
  121. Mac OS X
  122. Macromedia Flash
  123. Mainframe computer
  124. Malware
  125. Media center
  126. Media player
  127. Megabyte
  128. Microsoft
  129. Microsoft Windows
  130. Microsoft Word
  131. Mirror site
  132. Modem
  133. Motherboard
  134. Mouse
  135. Mouse pad
  136. Mozilla Firefox
  137. Mp3
  138. MPEG
  139. MPEG-4
  140. Multimedia
  141. Musical Instrument Digital Interface
  142. Netscape
  143. Network card
  144. News ticker
  145. Office suite
  146. Online auction
  147. Online chat
  148. Open Directory Project
  149. Open source
  150. Open source software
  151. Opera
  152. Operating system
  153. Optical character recognition
  154. Optical disc
  155. output
  156. PageRank
  157. Password
  158. Pay-per-click
  159. PC speaker
  160. Peer-to-peer
  161. Pentium
  162. Peripheral
  163. Personal computer
  164. Personal digital assistant
  165. Phishing
  166. Pirated software
  167. Podcasting
  168. Pointing device
  169. POP3
  170. Programming language
  171. QuickTime
  172. Random access memory
  173. Routers
  174. Safari
  175. Scalability
  176. Scrollbar
  177. Scrolling
  178. Scroll wheel
  179. Search engine
  180. Security cracking
  181. Server
  182. Simple Mail Transfer Protocol
  183. Skype
  184. Social software
  185. Software bug
  186. Software cracker
  187. Software library
  188. Software utility
  189. Solaris Operating Environment
  190. Sound Blaster
  191. Soundcard
  192. Spam
  193. Spamdexing
  194. Spam in blogs
  195. Speech recognition
  196. Spoofing attack
  197. Spreadsheet
  198. Spyware
  199. Streaming media
  200. Supercomputer
  201. Tablet computer
  202. Telecommunications
  203. Text messaging
  204. Trackball
  205. Trojan horse
  206. TV card
  207. Unicode
  208. Uniform Resource Identifier
  209. Unix
  210. URL redirection
  211. USB flash drive
  212. USB port
  213. User interface
  214. Vlog
  215. Voice over IP
  216. Warez
  217. Wearable computer
  218. Web application
  219. Web banner
  220. Web browser
  221. Web crawler
  222. Web directories
  223. Web indexing
  224. Webmail
  225. Web page
  226. Website
  227. Wiki
  228. Wikipedia
  229. WIMP
  230. Windows CE
  231. Windows key
  232. Windows Media Player
  233. Windows Vista
  234. Word processor
  235. World Wide Web
  236. Worm
  237. XML
  238. X Window System
  239. Yahoo
  240. Zombie computer
 



MY COMPUTER
This article is from:
http://en.wikipedia.org/wiki/Mainframe_computer

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Mainframe computer

From Wikipedia, the free encyclopedia

 
For other uses, see Mainframe.
A Honeywell-Bull DPS 7 mainframe, circa 1990.
A Honeywell-Bull DPS 7 mainframe, circa 1990.

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 refers primarily to IBM System z9 mainframes, the lineal descendants of the System/360, but it is also used for the lineal descendents of the Burroughs large systems and the UNIVAC 1100/2200 series mainframes.

Description

Modern mainframe computers have abilities not so much defined by their single task computational speed (Gbops or Gigahertz) 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 defined by high availability, one of the main reasons for their longevity, as they are used in applications where downtime would be costly or catastrophic. The term Reliability, Availability and Serviceability (RAS) is a defining characteristic of mainframe computers.

In the 1960s, most mainframes had no user interface per se. They accepted sets of punch cards and operated solely in batch mode to support back office functions. Teletype devices were also common, especially for system operators. By the early 1970s, many mainframes acquired interactive user interfaces and operated as timesharing computers, supporting hundreds or thousands of users simultaneously along with batch processing. Users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software. Many mainframes supported graphical terminals (and terminal emulation) by the 1980s (if not earlier). In 1990, an IBM mainframe became the first Web server located anywhere outside Switzerland's CERN organization (see: History of the World Wide Web), and nowadays most mainframes have partially or entirely phased out user terminal access.

Historically mainframes acquired their name in part because of their substantial size and requirements for specialized HVAC and electrical power. Those requirements ended by the mid-1990s, with CMOS mainframe designs replacing the older bipolar technology.

An IBM z890 mainframe, circa 2004. This model is 1.94 meters tall and occupies 1.24 square meters of floorspace.
An IBM z890 mainframe, circa 2004. This model is 1.94 meters tall and occupies 1.24 square meters of floorspace.

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 three levels of virtualization: logical partitions (LPARs, via the PR/SM facility), virtual machines (via the z/VM operating system), and through its operating systems (notably z/OS with its key-protected address spaces and sophisticated goal-oriented workload scheduling, but also 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 unsurprisingly take that view at least at times, and so do some independent analysts. However, the general consensus (held by Gartner and other independent analysts) is that the modern mainframe often has unique value and superior cost-effectiveness, especially for large scale enterprise computing. In fact, 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, and many vendors are promoting virtualization technologies, in many ways validating the mainframe's design accomplishments.

Mainframes also have unique execution integrity characteristics for fault tolerant computing. System 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 has its own large research and development organization to introduce new, homegrown mainframe 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 date 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, ICL in the United Kingdom, and Fujitsu, Hitachi, and NEC in Japan. The Soviet Union and Warsaw Pact countries manufactured close copies of IBM mainframes during the Cold War.

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 became a division of Sperry) which 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 price and offer local users much greater control over their own systems given the IT policies and practices at that time. 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 open source software combined with mainframe hardware RAS. Rapid expansion and development in emerging markets, particularly China, is also spurring major mainframe investments to solve exceptionally difficult computing problems, e.g. providing unified, extremely high volume online transaction processing databases for 1 billion consumers across multiple industries (banking, insurance, credit reporting, government services, etc.)

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 comparatively 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 referring 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

  • Historically 85% of all mainframe programs were written in the COBOL programming language. The remainder included a mix of PL/I (about 5%), Assembly language (about 7%), and miscellaneous other languages. eWeek estimates that millions of lines of net new COBOL code are still added each year, and there are nearly 1 million COBOL developers worldwide, with growing numbers in emerging markets. That said, COBOL is decreasing as a percentage of the total mainframe lines of code in production. Java, C, and C++ are all growing faster, especially Java.
  • Mainframe COBOL has recently acquired numerous Web-oriented features, such as XML parsing, with PL/I following close behind in adopting modern language features.
  • 90% of IBM's mainframes have CICS transaction processing software installed.[1] Other software staples include the IMS and DB2 databases, and WebSphere MQ and WebSphere Application Server middleware.
  • As of 2004, IBM claimed over 200 new (21st century) mainframe customers customers that had never previously owned a mainframe. Many are running Linux, some exclusively. There are new z/OS customers as well, frequently in emerging markets and among companies looking to improve service quality and reliability (perhaps because of previous non-mainframe server failures).
  • In May, 2006, IBM claimed that over 1,700 mainframe customers are running Linux. Nomura Securities of Japan spoke at LinuxWorld in 2006 and is one of the largest publicly known, with over 200 IFLs in operation that replaced rooms full of distributed servers.
  • Most mainframes run continuously at over 70% busy. A 90% figure is typical, and modern mainframes tolerate sustained periods of 100% CPU utilization, queuing work according to business priorities without disrupting ongoing execution.
  • Mainframes have a historical reputation for being "expensive," but the modern reality is much different. As of late 2006, it is possible to buy and configure a complete IBM mainframe system (with software, storage, and support), under standard commercial use terms, for about $50,000 (U.S.), equivalent to approximately 50% of the full annual cost of only one IT employee. The price of z/OS starts at about $1,500 (U.S.) per year, including 24x7 telephone and Web support.[2]

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 26 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 .[3]

The MIPS measurement has long been known 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, and virtualization capabilities make comparative measurements even more difficult. 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.

To give some idea of real world experience, it is typical for a single mainframe CPU to execute the equivalent of 50, 100, or even more distributed processors' worth of business activity, depending on the workloads. Merely counting processors to compare server platforms is extremely perilous.

See also

  • Supercomputer
  • SUSE Linux Enterprise Server
  • Red Hat Enterprise Linux

References

  1. ^ CICS-An Introduction. IBM. Retrieved on 2006-10-22.
  2. ^ My Personal Mainframe?. The Mainframe Blog. Retrieved on 2006-11-30.
  3. ^ Disputed. The 221,248 MIPS figure assumes 16 CPs per frame. This MIPS figure appears incorrect (too low) since 32 may be a system limit, not an LPAR limit. Also, z/OS LPARs can now span more than 16 CPs.

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"