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Computer

Specialty Definition: Computer

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Specialty Definition: Apple Macintosh

(From Wikipedia, the free Encyclopedia)

The Macintosh, now correctly called the Mac (since its introduction, Apple has officially changed the name of the computer to Mac), is a family of personal computers manufactured by Apple Computer, based in Cupertino, California, USA.

Launched in January, 1984 with a famous Super Bowl commercial, it was the first computer to popularize the graphical user interface (GUI, pronounced "gooey").

The operating system, simply called the System Software or System, officially became known as the Mac OS as of version 7.6. In March 2001, Apple introduced a modern and secure Unix-based successor, Mac OS X.

From its inception, the Macintosh has introduced or popularized a number of innovations adopted later by other PCs and operating systems:

• A graphical user interface, icons, a desktop, etc.
• The use of a mouse or other pointing device in personal computing (later, the standardization of an optical mouse on all desktop machines)
• WYSIWYG text and graphics editing ("what you see is what you get")
• Long file names (originally 31 characters, now 255)
• The PostScript laser printer
• Desktop publishing
• The SCSI interface
• Audio (both speakers and microphone) as a standard feature
• A CD-ROM drive as a standard feature
• Windows that may span multiple monitors
• Ethernet support as standard feature
• FireWire, also known as IEEE 1394 or iLink (Sony)
• AirPort wireless networking, also known as IEEE 802.11b and IEEE 802.11g
• The introduction of the 3.5" floppy disk as a standard feature (Macintosh, 1984)
• The abandonment of the floppy disk (iMac August 1998 and Power Macintosh G3 Blue & White January 1999)
• The first commercially available computer to feature USB for peripheral connection.
• A modern RISC-based architecture in the form of the PowerPC processor, developed jointly by Apple, IBM and Motorola (Power Macintosh 6100, 1994)

• Aesthetic and ergonomical industrial design

History

Steve Jobs and a number of Apple engineers visited Xerox PARC in 1979, three months after the Lisa and Macintosh projects had begun. They had been invited by Xerox, an investor in Apple, to see the Xerox Alto and Xerox Star computers, which were pioneers in usable GUI user interface technology. There is debate over the degree of impact that this visit had on Apple's products -- Apple's GUIs ended up working and looking different from the PARC GUIs, and GUIs had been an active area of computing research since the late 1960s -- but it is clear that the Xerox visits were extremely influential on the development of the Lisa and Macintosh.

The Macintosh's predecessor, the Lisa computer, was introduced in January 1983 for a price of $9,995.00 with many of the GUI-related innovations later seen on the Macintosh. It was aimed at business customers but was too much of a hard sell at the time; it was not a success for Apple, and the line was discontinued in 1986.

The Macintosh was introduced on January 22, 1984, with a famous Super Bowl commercial featuring a female athlete throwing a hammer through a giant image of a dictator ("Big Brother", vaguely reminiscent of the dominant computer maker at that time: IBM). The Mac went on sale two days later for a price of $2,495.00.

Although the Mac garnered an immediate enthusiastic following, it was too radical of a departure for most. Since the machine was entirely designed around the GUI, existing command-line programs had to be redesigned and rewritten, a challenging undertaking that many software developers shied away from, which initially led to a lack of software for the new system.

In 1985, the combination of the Mac and its GUI with Adobe PageMaker and Apple's LaserWriter printer enabled a low-cost solution for designing and previewing printed material, an activity that came to be known as desktop publishing. Interest in the Mac exploded, and it has continued to be the standard platform for publishing and printing houses.

By the early 1990s, it was thought by some that RISC-architecture CPUs would soon dramatically outpace the speed increases occurring over the same time in CISC CPUs such as the Macintosh's Motorola 68000 series and Intel's Pentium series. The AIM alliance of Apple Computer, IBM and Motorola was announced to create a series of RISC CPUs called the PowerPC. Existing Macintosh software that had been written for the 68000 series CPUs -- including some large sections of the Mac OS -- were made to run with a software emulator. The PowerPC remains the Macintosh CPU to date, although the architectural benefits and speed differences of RISC versus CISC remain controversial.

In 2000, the Macintosh made a second fundamental change, this time in its operating system, by switching to the Mach and BSD Unix-based Mac OS X.

See List of Macintosh models grouped by CPU.

Clones

The Apple II and IBM PC computer lines had been "cloned" by other manufacturers who had reverse engineered the minimal amount of firmware in the computers' ROM chips and subsequently legally produced computers that would run the same software. These clones were seen by Apple as a threat; Apple II sales had presumably suffered from the competition provided by Franklin Computer Corporation and its ilk. (Subsequently, the threat proved to be real; today, Dell Computer, Gateway Computer, and Hewlett-Packard all sell more IBM PC compatible computers than IBM does.)

The Macintosh's system software strategy was created with an eye toward suppressing any Mac clones. The Macintosh system software was a very large amount of complicated code that embodied the Mac's entire set of APIs, including the use of the GUI and file system, and a large amount of this system software was included in the Macintosh's ROM chips. Hence any competitor who attempted to create a Macintosh clone would have to either illegally duplicate all the copyrighted code in the ROMs -- in which case Apple could legally squash the manufacturer -- or reverse-engineer the ROMs, which would have been an enormous and costly process without certainty of success.

The strategy was successful; for years, several manufacturers created Macintosh clones, but they obtained their ROMs by actually purchasing one of Apple's Macintosh computers and removing from it the required parts, then installing those parts in the clone's case. This resulted in very expensive clones that were never popular, and Apple could safely say that its share of the Macintosh computer market was not in danger.

However, by 1995, Apple owned only about 7% of the worldwide market share of computers, and decided to launch a clone program, by which it would license the Macintosh ROMs and system software to other manufacturers who agreed to pay a royalty. The aim was to increase Apple's market share in the desktop computer market. From early 1995 to mid-1997, it was possible to buy PowerPC-based clone computers, running Mac OS, from Motorola, Power Computing, and Umax. The styling on the Mac clones often more closely resembled that of a PC than of a Mac, but the clones frequently offered a lower price and sometimes better performance.

Soon after Steve Jobs' return to Apple, he terminated the clone program. He stated that the clone program was ill-conceived and had been a result of "institutional guilt", meaning that there had been a widely held belief at Apple that had the company aggressively pursued a legal cloning program early in the history of the Macintosh, consumers might have turned to low-priced Macintosh clones rather than low-priced IBM PC compatible computers, and Apple might have ended up in the position currently occupied by Microsoft -- an extremely profitable company with low margins with a wide base of consumers perpetually dependent on its system software products. By now, Jobs stated, it was too late for this to happen; the clone program was doomed to failure from the start; and since Apple mostly made money by selling computer hardware, for the most part, it ought not engage in a licensing program to reduce its hardware sales.

Models

• iBook
• iMac
• Mac II
• Mac Plus
• Mac SE
• Classic
• PowerBook
• PowerBook G3
• PowerBook G4
• Power Macintosh
• Power Macintosh G3
• Power Macintosh G4
• Power Macintosh G4 Cube
• Power Macintosh G5
• Xserve

See also:

• AirPort networking
• AppleScript
• Apple v. Microsoft
• Carbon programming
• Cocoa programming
• Firewire
• .Mac
• Macworld Conference & Expo
• WYSIWYG

External links

• Articles from Jef Raskin about the history of the Macintosh

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Apple Macintosh."

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Computer

(From Wikipedia, the free Encyclopedia)

simple:Computer

The word computer used to mean a person who computes. In current language, a computer is any device used to process information according to a well-defined procedure. The word was originally used to describe people employed to do arithmetic calculations, with or without mechanical aids, but was transferred to the machines themselves. Originally, the information processing was almost exclusively related to arithmetical problems, but modern computers are used for many tasks unrelated to mathematics. Within such a definition sit mechanical devices such as the slide rule, the gamut of mechanical calculators from the abacus onwards, as well as all contemporary electronic computers. The first program-controlled computers are Konrad Zuse's Z1 (1936) and Z3 (1941).

Definitions

However, the above definition includes many special-purpose devices that can compute only one or a limited range of functions. When considering modern computers, their most notable characteristic that distinguishes them from earlier computing devices is that, given the right programming, any computer can emulate the behaviour of any other (though perhaps limited by storage capacity and at different speeds), and, indeed, it is believed that current machines can emulate any future computing devices we invent (though undoubtedly more slowly). In some sense, then, this threshold capability is a useful test for identifying "general-purpose" computers from earlier special-purpose devices. This "general-purpose" definition can be formalised into a requirement that a certain machine must be able to emulate the behaviour of a universal Turing machine. Machines meeting this definition are referred to as Turing-complete.

Embedded Computers

In the last 20 years or so, however, many household devices, notably including video game consoles but extending to mobile telephones, video cassette recorders, PDA's and myriad other household, industrial, automotive, and other electronic devices, all contain computer-like circuitry capable of meeting the above Turing-completeness requirement (with the proviso that the programming of these devices is often hardwired into a ROM chip which would need to be replaced to change the programming of the machine). These computers inside other special-purpose devices are commonly referred to as "microcontrollers" or "embedded computers". Therefore, many restrict the definition of computers to devices whose primary purpose is information processing rather than being a part of a larger system such as a telephone, microwave oven, or aircraft, and can be adapted for a variety of purposes by the user without physical modification. Mainframe computers, minicomputers, and personal computers are the main types of computers meeting this definition.

Personal Computers

Finally, many people who are unfamiliar with other forms of computers use the term exclusively to refer to personal computers.

How Computers Work

While the technologies used in digital computers have changed dramatically since the first computers of the 1940s (see History of computing hardware for more details), most still use the von Neumann architecture proposed in the early 1940s by John von Neumann.

Von Neumann's architecture describes a computer with four main sections: the Arithmetic and Logic Unit (ALU), the control circuitry, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by a bundle of wires, a "bus."

Memory

In this system, memory is a sequence of numbered "cells" or "pigeon holes," each containing a small piece of information. The information may be an instruction to tell the computer what to do. The cell may contain data that the computer needs to perform the instruction. Any slot may contain either, and indeed what is at one time data might be instructions later.

In general, memory can be rewritten over millions of times - it is a scratchpad rather than a stone tablet.

The size of each cell, and the number of cells, varies greatly from computer to computer, and the technologies used to implement memory have varied greatly - from electromechanical relays, to mercury-filled tubes (and later springs) in which acoustic pulses were formed, to matrices of permanent magnets, to individual transistors, to integrated circuits with millions of capacitors on a single chip.

Processing

The arithmetic and logical unit, or ALU, is the device that performs elementary operations such as arithmetic operations (addition, subtraction, and so on), logical operations (AND, OR, NOT), and comparison operations (for example, comparing the contents of two "slots" for equality). This unit is where the "real work" is done.

The control unit keeps track of which slot contains the current instruction that the computer is performing, telling the ALU what operation to perform and retrieving the information (from the memory) that it needs to perform it, and transfers the result back to the appropriate memory location. Once that occurs, the control unit goes to the next instruction (typically located in the next slot, unless the instruction is a jump instruction informing the computer that the next instruction is located in another location).

Input and Output

The I/O allows the computer to obtain information from the outside world, and send the results of its work back there. There are incredibly broad range of I/O devices, from the familiar keyboardss, monitors and floppy disk drives, to the more unusual such as webcams.

Instructions

The instructions discussed above are not the rich instructions of a human language. A computer only has a limited number of well-defined, simple instructions. Typical sorts of instructions supported by most computers are "copy the contents of cell 123, and place the copy in cell 456", "add the contents of cell 666 to cell 042, and place the result in cell 013", and "if the contents of cell 999 are 0, your next instruction is at cell 345".

Instructions are represented within the computer as numbers - the code for "copy" might be 001, for example. The particular instruction set that a specific computer supports is known as that computer's machine language. In practice, people do not normally write the instructions for computers directly in machine language but rather use a "high level" programming language which is then translated into the machine language automatically by special computer programs (interpreters and compilers). Some programming languages map very closely to the machine language, such as assembler (low level languages); at the other end, languages like Prolog are based on abstract principles far removed from the details of the machine's actual operation (high level languages).

Architecture

Contemporary computers put the ALU and control unit into a single integrated circuit known as the Central Processing Unit or CPU. Typically, the computer's memory is located on a few small integrated circuits near the CPU. The overwhelming majority of the computer's mass is either ancilliary systems (for instance, to supply electrical power) or I/O devices.

Some larger computers differ from the above model in one major respect - they have multiple CPUs and control units working simultaneously. Additionally, a few computers, used mainly for research purposes and scientific computing, have differed significantly from the above model, but they have found little commercial application.

The functioning of a computer is therefore in principle quite straightforward. The computer fetches instructions and data from its memory. The instructions are executed, the results are stored, and the next instruction is fetched. This procedure repeats until the computer is turned off.

Programs

Computer programs are simply large lists of instructions for the computer to execute, perhaps with tables of data. Many computer programs contain millions of instructions, and many of those instructions are executed repeatedly. A typical modern PC (in the year 2003) can execute around 2-3 billion instructions per second. Computers do not gain their extraordinary capabilities through the ability to execute complex instructions. Rather, they do millions of simple instructions arranged by clever people, "programmers." Good programmers develop sets of instructions to do common tasks (for instance, draw a dot on screen) and then make those sets of instructions available to other programmers.

Nowadays, most computers appear to execute several programs at the same time. This is usually referred to as multitasking. In reality, the CPU executes instructions from one program, then after a short period of time, it switches to a second program and executes some of its instructions. This small interval of time is often referred to as a time slice. This creates the illusion of multiple programs being executed simultaneously by sharing the CPU's time between the programs. This is similar to how a movie is simply a rapid succession of still frames. The operating system is the program that usually controls this time sharing.

Operating System

The operating system is a sort of catch-all of useful pieces of code. Whenever some kind of computer code becomes sharable by many different types of computer program, over many years, programmers eventually move it into the operating system.

The operating system, for example, decides which programs get to run, and when, and what resources (such as memory or I/O) they get to use. The operating system also provides services to other programs, such as code ("drivers") which allow programmers to write programs for a machine without needing to know the intimate details of all attached electronic devices.

Now widely used programs are starting to be included in the operating system just because it is an economical way to distribute them. It's now commonplace for operating systems to include web browsers, text editors, e-mail programs, network interfaces, movie-players and other programs that were once quite exotic special-order programs.

Uses of computers

The first digital computers, with their large size and cost, mainly performed scientific calculation. ENIAC, an early US computer, calculated neutron cross-sectional densities to see if the hydrogen bomb would work properly. The CSIR Mk I, the first Australian computer, evaluated rainfall patterns for the catchment of the Snowy Mountains scheme, a large hydroelectric generation project. Others were used in cryptanalysis, for example the world's first programmable digital electronic computer, Colossus, built during World War II. However, early visionaries also anticipated that programming would allow chess playing, moving pictures and other uses.

People in governments and large corporations also used computers to automate many of the data collection and processing tasks previously performed by humans - for example, maintaining and updating accounts and inventories. In academia, scientists of all sorts began to use computers for their own analyses. Continual reductions in the costs of computers saw them adopted by ever-smaller organizations. Businesses, organizations, and governments often employ a large number of small computers to accomplish tasks that were previously done by an expensive, large mainframe computer. Collections of the smaller computers in one location is referred to as a server farm.

With the invention of the microprocessor in the 1970s, it became possible to produce very inexpensive computers. Personal computers became popular for many tasks, including keeping books, writing and printing documents. Calculating forecasts and other repetitive math with spreadsheets, communicatiing with e-mail and, the Internet. However, computers' wide availability and easy customization has seen them used for many other purposes.

At the same time, small computers, usually with fixed programming, began to find their way into other devices such as home appliances, automobiles, aeroplanes, and industrial equipment. These embedded processors controlled the behaviour of such devices more easily, allowing more complex control behaviours (for instance, the development of anti-lock brakes in cars). By the start of the twenty-first century, most electrical devices, most forms of powered transport, and most factory production lines are controlled by computers. Most engineers predict that this trend will continue.

The word "computer"

Over the years there has been several slightly different meanings to the word computer, and several different words for the thing we now usually call a computer.

For instance "computer" was once commonly used to mean a person employed to do arithmetic calculations, with or without mechanical aids. According to the Barnhart Concise Dictionary of Etymology, the word came into use in English in 1646 as a word for a "person who computes" and then by 1897 also for a mechanical calculating machine. During World War II it referred e.g. to U.S. and British servicewomen whose job it was to calculate the trajectories of large artillery shells with such machines.

Charles Babbage designed one of the first computing machines called the Analytical engine, but due to technological problems it was not built in his lifetime. Various simple mechanical devices such as the slide rule kind have also been called computers. In some cases they were referred to as "analog computers", as they represented numbers by continuous physical quantities rather than by discrete binary digits. What are now called simply "computers" were once commonly called "digital computers" to distinguish them from these other devices (which are still used in the field of analog signal processing, for example).

In thinking of other words for the computer, it is worth noting that in other languages the word chosen does not always have the same literal meaning as the English language word. In French for example, the word is "ordinateur", which means approximately "organizer", or "sorting machine". The Spanish word is "ordenador" , with the same meaning, although in some countries they use the anglicism computadora. In Italian, computer is "calcolatore", calculator, emphasizing its computational uses over logical ones like sorting. In Swedish, a computer is called "dator" from "data". At least in the 1950s, they were called "matematikmaskin" ("mathematics machine"). In Chinese, a computer is called "dian now" or an "electric brain". In English, other words and phrases have been used, such as "data processing machine".

See Also

• computer expo
• computer science
• computing
• computing analogies
• computers in fiction
• digital
• history of computing

Computer Types

• analog computer
• pulse computer

• microcomputer
  • home computer
  • personal computer
  • server
• minicomputer
• mainframe computer
• supercomputer

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computer."

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Computer crime

(From Wikipedia, the free Encyclopedia)

Computer crime or e-crime is crime in which a computer plays an essential part.

Exactly what is illegal varies greatly from territory to territory. Consequently, the growth of international data communications and in particular the Internet has made these crimes both more common and more difficult to police.

Examples of computer crime are:

• Fraud achieved by the manipulation of computer records.
• Spamming where this is outlawed completely or where regulations controlling it are violated.
• Deliberate circumvention of computer security systems.
• Unauthorised access to or modification of
  • programs (see hacking).
  • data.
• Industrial espionage by means of access to or theft of computer materials.
• Identity theft where this is accomplished by use of fraudulent computer transactions.
• Writing or spreading computer viruses or worms.
• Salami slicing is the practice of stealing money repeatedly in extremely small quantities

External links

• Australian Computer Abuse Research Bureau (ACARB) introduction to computer abuse concepts

Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computer crime."

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Computer game

(From Wikipedia, the free Encyclopedia)

A computer game is any sort of game that is played using a computer.

A computer game is not necessarily a video game, or vice versa; for instance a text-based role-playing game could be played verbally by a blind person, which is clearly no longer a "video" game, and the first generation of video games, such as Pong, used dedicated electronic circuitry not even remotely resembling a computer.

The usual distinction today is rather subtle; a game will be a "computer game" if it is played on a general-purpose computer, but a "video game" if it is played on a computer that is specialized for game playing. Computer games will typically feature a wider assortment of direct controls exploiting the full computer keyboard, while video games tend to use more layers of menus, or motion sequences (up-up-down-left, etc) via the game controller. The most important distinction between computer and video games arises from the fact that computers have high resolution monitors, optimized for viewing at close range by one person, while home video game consoles use a much lower-resolution commercial television as their output device, optimized for viewing at a greater distance. As a result, most computer games are intended for single-player or networked multi-player play, while many video games are designed for local multi-player play, with all players viewing the same TV set.

Formerly, video games tended to need and use less computing power than computer games, but with the increasing power of video game hardware, that distinction is nearly erased, and many games are now produced for both computers and video game systems. Video game manufacturers usually exercise tight control over the games that are made available on their systems, so unusual or special-interest games are more likely to only ever appear as games on general-purpose computers.

See also

• list of computer and video games by name
• list of computer and video games by category
• list of free game software

External links

• GameSpot: a large, corporately-owned database of gaming reviews, news, downloads, and forums
• Open Source Gaming: a database of gaming reviews, news, downloads, forums, image galleries, more specifically focused on games released under an Open Source license
• Linux Games: a news site with the latest on Linux game ports and releases.
• Download Free Games: a large freeware and shareware game download site
• Games Online: a selection of games to play free online

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computer game."

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Computer hardware

(From Wikipedia, the free Encyclopedia)

Hardware is a comprehensive term for all of the physical parts of a computer, as distinguished from the data it contains or operates on, and the software that provides instructions for the hardware to acoomplish tasks. The boundary between hardware and software is slightly blurry - firmware is software that is "built-in" to the hardware, but such firmware is usually the province of computer programmers and computer engineers in any case and not an issue that computer users need to concern themselves with.

A typical computer (Personal Computer, PC) contains in a desktop or tower case the following parts:

• Motherboard which holds the CPU, main memory and other parts, and has slots for expansion cards
• power supply - a case that holds a transformer, voltage control and fan
• storage controllers, of IDE, SCSI or other type, that control hard disk , floppy disk, CD-ROM and other drives; the controllers sit directly on the motherboard (on-board) or on expansion cards
• graphics controller that produces the output for the monitor
• the hard disk, floppy disk and other drives for mass storage
• interface controllers (parallel, serial, USB, Firewire) to connect the computer to external peripheral devices such as printers or scanners

• Computer architecture
  • Central Processing Unit - CPU
  • Motherboard
    • PCI Bus
    • ISA Bus
    • USB
    • AGP
• Storage
  • Compact disc
  • What is a disk versus what is a disc
  • DVD
  • Floppy disk
  • Hard disk
  • Punch card
  • RAM
  • Tape Drive
• Input/Output
  • Braille Embosser
  • CD-ROM
  • Keyboard
  • Monitor
  • Computer terminal
  • Mouse
  • Computer Speech Recognition
  • Computer Speech Synthesis
  • DVD-ROM
  • Digitizing Tablet
  • Graphics card
  • Joystick
  • Joypad
  • Modem
  • Network card
  • Plotter
  • Printer
  • Refreshable Braille Display
  • Scanner
  • Sound card
  • Touch screen
  • Trackball
  • Webcam
  • Pointing devices
  • used laptop/notebook and spares [[1]

See also

• legacy system
• Open hardware
• optical computer
• DNA computer
• Origins of computer terms

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computer hardware."

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Computer process

(From Wikipedia, the free Encyclopedia)

A computer process is, roughly speaking, a task being run by a computer, often simultaneously with many other tasks. Many processes may exist simultaneously but they must take turns on the CPU (unless there are multiple CPU's available).

Processes are often called tasks in embedded operating systems. The sense of 'process' is 'something that takes up time', as opposed to 'memory', which is 'something that takes up space'. Kaare Christian noted it was as if 'processes have "life"'.

Processes are typically managed by the operating system, which keeps them separated and allocates the resources they need so that they are less likely to interfere with each other and cause system failures. The operating system may also provide mechanisms for inter-process communication to enable processes to interact in safe and predictable ways.

In general, a process consists of:

• Memory, (typically a region of virtual memory for suspended processes) which contains executable code or task-specific data.
• Operating system resources that are allocated to the process, such as file descriptors (Unix terminology) or handles (Windows).
• Security attributes, such as the process owner and the process's set of permissions.
• Processor state, such as the content of registers, physical memory addresses, etc.. The state is stored in the actual registers when the process is executing, and in memory otherwise.

The last item, processor state, is associated with each of the process's threads in operating systems that support threads.

At this level of programming, the registers are the least available resource, and the program values must be loaded from memory into the registers, which are first re-set, and then loaded. These steps occur at the clock rate of the CPU and depend on the processor architecture.

If a task is suspended, then it is eligible for swapping to disk, similarly to residence in virtual memory, where blocks of memory values are really on disk and not in physical memory. The block sizes depend on the operating system.

See Also

• Computer multitasking
• Zombie process

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computer process."

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Computer science

(From Wikipedia, the free Encyclopedia)

simple:Computer science zh-cn: %E8%AE%A1%E7%AE%97%E6%9C%BA%E7%A7%91%E5%AD%A6

In its most general sense, computer science (CS) is the study of computation, both in hardware and in software. In practice, CS includes a variety of topics relating to computers, which range from the abstract analysis of algorithms to more concrete subjects like programming languages, software, and computer hardware. As a scientific discipline, it is a very different activity from computer programming and computer engineering, although the three are often confused.

The Church-Turing thesis states that all known kinds of general computing devices are essentially equivalent in what they can do, although they vary in time and space efficiency. This thesis is sometimes treated as the fundamental principle of computer science. Computer scientists usually emphasize von Neumann computerss or Turing machines (computers that do one small, deterministic task at a time), because that resembles most real computers in use today. Computer scientists also study other kinds of machines, some practical (like parallel and quantum machines) and some theoretical (like random and oracle machines).

CS studies what programs can and cannot do (computability and artificial intelligence), how programs should efficiently evaluate specific results (algorithms), how programs should store and retrieve specific bits of information (data structures), and how programs and people should communicate with each other (user interfaces and programming languages).

CS has roots in electrical engineering, mathematics and linguistics. In the last third of the 20th century computer science has become recognized as a distinct discipline and has developed its own methods and terminologies.

The first computer science department was founded at Purdue University in 1962. Most universities today have CS departments.

The highest honor in computer science is the Turing Award, the winners of which are all major pioneers in the field.

Computer science is no more about computers than astronomy is about telescopes

- Edsger Dijkstra

Related fields

Computer science is closely related to several other fields. These fields overlap considerably, though important differences exist

• Information science is the study of data and information, including how to interpret, analyze, store, and retrieve it. Information science started as the foundation of scientific analysis of communication and databases.
• Software engineering emphasizes analysis, design, and construction of useful software using contemporary tools and practices.
• Information systems is the application of computing to support the operations of an organization: operating, installing, and maintaining the computers, software, and data. Management information systems is a key subfield that emphasizes financial and personnel management.
• Computer engineering is about the analysis, design, and construction of computer hardware.
• Information security is about the analysis and implementation of information system security (cryptography is included).

Major subfields

Mathematical foundations

• Boolean algebra
• Discrete mathematics
• Graph theory
• Information theory
• Symbolic logic
• Probability and Statistics

Theoretical computer science

• Algorithmic information theory
• Compilers
  • Lexical analysis
  • Parsing
• Computability theory
• Cryptography
• Denotational semantics
• Theory of computation (or theoretical computer science)
  • analysis of algorithms and problem complexity
  • logics and meanings of programs
  • mathematical logic and formal languages
• Type theory

Hardware

(see also electrical engineering)

• control structures and Microprogramming
• arithmetic and logic structures
• memory structures
• input/output and data communications
• logic design
• integrated circuits
  • VLSI design
• performance and reliability

Computer systems organization

(see also electrical engineering)

• Computer architecture
• Computer networks
  • Distributed computing
• performance of systems
• computer system implementation

Software

• Computer program and Computer programming
  • Parallel Programming
  • Program specification
  • Program verification
• programming techniques
• Software engineering
  • Optimization
  • Software metrics
  • Design patterns
• Programming languages
• Operating Systems

Data and information systems

• Data structures
• data storage representations
• data encryption
• Data compression
• coding and information theory
• files
  • File formats
• information systems
  • Databases
  • information storage and retrieval
  • information interfaces and presentation

Computing methodologies

• symbolic and algebraic manipulation
• Artificial intelligence
• Computer graphics
• Image processing and computer vision
• Pattern recognition
  • Speech recognition
• simulation and modeling
• document and text processing
• Digital signal processing

Computer applications

• administrative data processing
• mathematical software
  • Numerical analysis
  • Automated theorem proving
  • Computer algebra
• physical sciences and engineering
  • Computational chemistry
  • Computational physics
• life and medical sciences
  • Bioinformatics
  • Computational Biology
  • Medical informatics
• social and behavioral sciences
• arts and humanities
• computer-aided engineering
• Robotics
• Human-computer interaction
  • Speech synthesis
  • Usability engineering

Computing milieux

• the computer industry
• History of computing hardware
• computers and education
• computers and society
  • Computer supported cooperative work
• legal aspects of computing
• management of computing and information systems
• personal computing

• Computer and information security

History

• History of computing
• Origins of computer terms
• Early programming projects
• Computer science departments
• Timeline of algorithms

Prominent pioneers in computer science

• John Backus Invention of FORTRAN, the first practical high-level programming language and the Backus-Naur form for describing formal language syntax.
• James Cooley and John Tuckey The Fast Fourier Transform and its impact on scientific research..
• Ole-Johan Dahl and Kristen Nygaard, inventors of the proto-object oriented language SIMULA.
• Edsger Dijkstra for algorithms, Goto cosidered harmful, rigor, and pedagogy.
• Kenneth Iverson Inventor of APL, for his contribution to interactive computing.
• William Kahan for the IEEE floating-point standard. (Perhaps this reference should be moved to hardware engineering)
• Donald Knuth for the Art of Computer Programming
• Ada Lovelace famous as the world's first ever computer programmer
• John von Neumann for devising the von Neumann architecture.
• Claude E. Shannon for information theory.
• Alan Turing for computability theory.
• James Wilkinson The technique of "backward error analysis" and advances in the field of matrix computations. Wilkinson was also a principal mover in the development of the Pilot ACE, the first British computer, in the late 1940s. (see more on Wilkinson in the MacTutor Biographies.)
• Konrad Zuse Builder of the first binary computer in the 1930s, for which he devised a programming language well ahead of its times.

See list of computer scientists for many more notables.

See also

• Computing
• History of computing
• History of computing hardware
• Turing Award (ACM)
• IEEE John von Neumann Medal
• Computer jargon
• Computer slang
• Computer science basic topics
• Computing analogies
• Internet
• Multimedia
• Data acquisition
• Benchmark
• Sensor network
• Online computations and algorithms,
• Computer numbering formats

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computer science."

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Computing

(From Wikipedia, the free Encyclopedia)

Originally the word computing was synonymous with counting and calculating, and a computer was a person who computes. Since the advent of the electronic computer, it has come to also mean the operation and usage of these machines, as well as the electrical processes carried out within the computer hardware itself.

Science and Theory

• Computer science
• Theory of computation
• DBLP December 2003: 450 000 bibliographic entries on Computer Science

Hardware

• Computer hardware
• Computer network
• Computer system
• History of computing hardware

Software

• Software engineering
• Computer programming
• Computer software
  • Software patent

History of computing

Business computing

• Accounting software
• Computer aided design
• Computer aided manufacturing
• Customer relationship management
• Data warehouse
• Decision support system
• Electronic data processing
• Enterprise resource planning
• Geographic information system
• Management information system
• Material resource planning
• Strategic enterprise management
• Supply chain management

Human factors

• Accessible computing
• Human-computer interaction (Geek Speak)

Computer security

• Cryptology - cryptography - information theory
• Cracking - demon dialing - Hacking - war dialing - war driving
• Dumpster diving
• Physical security
• Batch job
• Computer insecurity
• Computer surveillance
• defensive programming
• security engineering

Data

Numeric Data

• integral data types - bit, byte, etc.
• real data types: Float (Floating Point, Single Precision, Double Precision, Fixed Precision, Fixed Width)
• Binary Coded Decimal (BCD)
• representation: Binary - Octal - Decimal - Hexadecimal (hex)
• Computer mathematics - Computer numbering formats -

Character Data

• storage: Character - String - Text - Plain text
  • representation: ASCII - Unicode - Multibyte - EBCDIC (Widecharacter, Multicharacter)

Other Data Topics

• Data compression
• Digital signal processing
• Image processing
• Indexed

Mechatronics

Classes of computers

• Analog computer
• Desktop computer
• Desknote
• Digital computer
• Embedded computer
• Home computer
• Laptop
• Mainframe
• Minicomputer
• Microcomputer
• Personal computer
• Personal digital assistant (aka PDA, or Handheld computer)
• Server
• Supercomputer
• Tablet PC
• Video game console
• Workstation

Companies - current

• Apple Computer
• Dell
• Fujitsu
• Gateway
• Hewlett-Packard
• IBM
• Microsoft

Companies - historic

• English Electric
• Ferranti
• General Electric
  • ICL
• Leo
• Marconi
• Scientific Data Systems
• Univac
• Compaq
• DEC

Professional organisations

• Association for Computing Machinery (ACM)
• British Computer Society (BCS)
• Association for Survey Computing (ASC)
• Institute of Electrical and Electronics Engineers (IEEE), in particular the IEEE Computer Society
• International Electrotechnical Commission (IEC)

Standards organizations and consortia

(see also standardization)

• International Organization for Standardization (ISO)
• Institute of Electrical and Electronics Engineers (IEEE)
• Internet Engineering Task Force (IETF)
• World Wide Web Consortium (W3C)

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Computing."

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Home computer

(From Wikipedia, the free Encyclopedia)

Home Computer

• This article discusses the early commercial computers that tended to be used in the home—rather than for commercial purposes—during the 1980s.

• This breed of computer largely died out at the end of the decade (in the United States) or in the early 1990s (in Europe) due to the rise of the IBM PC compatible personal computer.

Home Computer is a consumer-friendly word for the first generation of microcomputers (the technical term that was previously used). The home computer became affordable for the general public due to the development of the silicon chip based microprocessor.

In a manner resembling the expansion of new animal forms in the Cambrian period, large numbers of new machines of all types, including such exotica as the Forth-based Jupiter ACE appeared on the market, and disappeared again. A few types remained for much longer, some, such as the BBC Micro and Commodore 64 still having a devoted following. However by the end of the decade most were squeezed out between the IBM compatible Personal Computer and the newer generations of video game consoles because they each used their own incompatible formats. The IBM revolution was caused by the 1981 release of the IBM PC (5150).

Many of these computers were superficially similar, having a usually very cheap-to-manufacture keyboard integrated into the processor unit and displaying output on a home television. Many used compact audio cassettes as a (notoriously unreliable) storage mechanism since floppy disk drives were very expensive at the time. Cheapness was the order of the day for most of these machines.

Almost all computers employ an operating system (OS) which acts as an interface between the operator and the computer's internal hardware (memory, CPU, etc). Home computers most often had their OS, of which one part was usually a BASIC interpreter, stored in one or more ROM chips. The term software commonly denoted application programs sitting 'above' the OS to perform a specific task, e.g. wordprocessors or games.

As many older computers have become obsolete it has become popular amongst enthusiasts to enable one type of computer to emulate another via the use of emulation software. Thus, many of the operating environments for the computers listed below can be recreated on a modern PC.

The home computer was commonly based on 8-bit microprocessor technology, typically the MOS Technologies 6502 or the Zilog Z80. During the early to mid-1980s a large variety of 8-bit home computers were designed and marketed. These were then gradually supplanted by the PC and its competing 16-bit (Motorola 68000-based) home/personal computers appearing from 1984 onwards.

See also

• Personal computer
• History of computing hardware II
• List of home computers
• List of home computers by category

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Home computer."

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Mainframe computer

(From Wikipedia, the free Encyclopedia)

Mainframes (often colloquially referred to as "big iron") are large, powerful, and expensive computers used mainly by large companies for bulk data processing (such as bank transaction processing).

The term arose during the early 1970s with the introduction of smaller computers such as the DEC PDP series, which became known as minicomputers, so users coined the term "mainframe" to describe larger, earlier types.

Description

Mainframe computers' abilities are not so much defined by their CPU speed as by their massive internal memory, large, high-capacity external storage, fast high-throughput I/O, high-quality internal engineering and resulting proven reliability, and expensive but high-quality technical support. These machines can and do run successfully for years without interruption, with repairs taking place whilst they continue to run. Mainframe vendors offer such services as off-site redundancy—if a machine does break down, the vendor offers the option to run customers' applications on their own machines (often without users even noticing the change) whilst repairs go on. The internal redundancy of these computers can be such that, in at least one reported case, technicians could move one from one site to another by disassembling it piece by piece, and reassembling it at the new site, whilst leaving the machines running. The switchover in this example took place entirely transparently.

Often, mainframes support thousands of simultaneous users who gain access through "dumb" terminals.

Some 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 hundreds of smaller PCs, reducing management and administrative costs while providing greatly improved scalability and reliability. The reliability is improved because of the hardware redundancy noted above, and the scalability is achieved because hardware resources can be reallocated among the "virtual machines" as needed. This is much harder to do with PCs, because adding or removing hardware resources often requires the machine to be taken offline, and the hardware limitations are much more restrictive. When running as the host for many "virtual machines" a mainframe can provide the raw power for which they have always been valued, but also the flexibility provided by PC networks.

Currently, IBM mainframes are dominant in the market, with Hitachi, Amdahl, and Fujitsu also producing machines. Prices start at several hundred thousand dollars.

History

Several manufacturers produced mainframe computers in the 1960s and 1970s; in the 'glory days' it was "IBM and the Seven Dwarves": Burroughs, Control Data, General Electric, Honeywell, NCR, RCA, and Univac. But shrinking demand and tough competition caused a huge shakeout in the market—RCA sold out to Univac and GE also left; Honeywell was bought out by Bull, Univac merged with Sperry to form Sperry/Univac, which was later merged with Burroughs to form Unisys Corporation in 1986 (so-called "dinosaurs mating"). In 1991, AT&T briefly owned NCR.

Companies found that servers based on lower-cost microcomputer designs could be deployed at a fraction of the cost and offer local users much greater control of their own systems, and "dumb terminals" used for interacting with mainframe systems were gradually replaced by personal computers. Consequently, demand plummeted and mainframe installations were restricted mainly to financial institutions with massive data processing requirements. For a while, there was a consensus among industry analysts that the mainframe was a dying market, as mainframe platforms were increasingly replaced by personal computer networks.

This trend started to turn around in the late 1990s as corporations found new uses for their mainframes, since they can offer web server performance similar to that of hundreds of smaller machines, but with much lower power and administration costs.

Another factor currently increasing mainframe use is the development of the Linux operating system, which is capable of running on many mainframe systems, either directly or, more commonly, in a virtual machine. This allows mainframes to take advantage of the software and development expertise and communities from the PC market.

Comparison with supercomputers

The distinction between supercomputers and mainframes is not a hard and fast one, but generally one can say that supercomputers focus on problems which are limited by calculation speed while mainframes focus on problems which are limited by Input/Output and reliability. As a consequence:

• Supercomputers typically exploit massive parallelism, often with thousands of processors, while mainframes have a single or a small number (up to several dozen) of processors.
• Because of the parallelism visible to the programmer, supercomputers are quite complicated to program; in mainframes, the limited parallelism (if present) is usually hidden from the programmer.
• 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 accessed from databases.
• Supercomputers tend to cater to science and the military, while mainframes tend to target business and civilian government applications.

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Mainframe computer."

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Microcomputer

(From Wikipedia, the free Encyclopedia)

A microcomputer is a computer that has at its heart a microprocessor central processing unit. In most modern microcomputers the processor also has a short term storage (or cache memory) and input/output control circuits on the same integrated circuit (or chip).

The world's first commercial microprocessor was the Intel 4004, released on November 15 1971. The 4004 processed 4 binary digits (bits) of data in parallel; in other words, it was a 4-bit processor.

At the turn of the century 30 years later, microcomputers in embedded systems (built into home appliances, vehicles, and all sorts of equipment) most often are 8-bit, 16-bit or 32-bit. Desktop/consumer microcomputers, like PCss, are mostly 32-bit, while some science/engineering workstations as well as database and financial transaction servers are 64-bit (with one or more CPUs).

After the launch by IBM of their IBM PC, the term Personal Computer (q.v.) became generally used for a consumer-friendly microcomputer. The second generation of microcomputers (8-bit, early 1980s) were often referred to as home computers (q.v.).

It was the launch of the VisiCalc spreadsheet (for the Apple II) that first turned the microcomputer from a hobby for computer enthusiasts into a business tool.

See also:

• Mini computer
• Mainframe computer
• Supercomputer
• History of computing hardware II

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Microcomputer."

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Personal computer

(From Wikipedia, the free Encyclopedia)

Three Gigahertz personal computer and peripherals, October 2003. From left to right: printer (left of the irrelevant TV), monitor, broadband cable modem for the internet, scanner. The tower (CPU, hard drive, etc) can just be glimpsed at bottom right. The keyboard and mouse are wire-less.
Larger version

The term personal computer or PC has three meanings:

• IBM's range of PCs that lead to the use of the term - see IBM PC.

• A generic term used to describe microcomputers that are compatible with IBM's specification - (discussed here)

• A generic term sometimes used to describe all microcomputers - (mentioned here)

The first generation of microcomputers were sometimes known as home computers, and are discussed in that section.

A personal computer is an inexpensive microcomputer, originally designed to be used by only one person at a time, and which is IBM PC compatible - (though in common usage it may sometimes refer to non-compatible machines).

The earliest known use of the term was in New Scientist magazine in 1964, in a series of articles called "The World in 1984". In "The Banishment of Paper Work," Arthur L. Samuel of IBM's Watson Research Center writes, "While it will be entirely feasible to obtain an education at home, via one's own personal computer, human nature will not have changed."

The first generation of microcomputers that started to appear in the 1970s (see Home Computers) were markedly less versatile and powerful than business computers of the day, and were generally used by computer enthusiasts or for playing games.

It was the launch of the VisiCalc spreadsheet, initially for the Apple II and later for the IBM PC that became the "killer app" that turned the microcomputer into a business tool. The low cost of personal computers led to great popularity in the home and business markets during the 1980s. In 1982, Time magazine named the personal computer its Man of the Year.

During the 1990s, the power of personal computers increased radically, blurring the formerly sharp distinction between personal computers and multi-user computers such as mainframes. Today higher-end computers often distinguish themselves from personal computers by greater reliability or greater ability to multitask, rather than by straight CPU power.

Architecture and Expansion

Most modern personal computers use the IBM PC compatible hardware architecture, using x86-compatible processors made by Intel, AMD, or Cyrix. The hardware capabilities of personal computers can usually be extended by the addition of Expansion cards.

With regard to portability we can distinguish:

• the desktop computer
• the notebook or laptop
• the wearable computer

Non IBM compatible "Personal Computers"

Despite the overwhelming popularity of the personal computer, a number of non IBM PC compatible microcomputers (sometimes also generically called Personal Computers) are still popular in niche uses. The leading alternative is Apple Computer's proprietary Power Macintosh platform, based on the PowerPC computer architecture, which is widely used for grapic design and related uses.

See also:

• The Apple, Apple II, Lisa, and Macintosh
• Osborne 1
• 8-bit microcomputer
• desknote
• History of computing hardware II

• Microcomputer
• Minicomputer
• Mainframe computer
• Supercomputer
• Server

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Personal computer."

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Secure computing

(From Wikipedia, the free Encyclopedia)

A secure computing platform is designed so that those agents who should not be able to perform certain actions cannot do them, while those agents who should be able to perform certain actions can do them. The actions in question can be reduced to operations of access, modification and deletion.

It is important to understand that in a secure system, the legitimate users of that system are still able to do what they should be able to do. In the case of a computer system sequestered in a vault without any means of power or communication, the term 'secure' is applied in a pejorative sense only.

It is also important to distinguish the techniques employed to increase a system's security from the issue of that system's security status. In particular, systems which contain fundamental flaws in their security designs cannot be made secure without compromising their utility. Consequently, most computer systems cannot be made secure even after the application of extensive "computer security" measures.

There are two different cultures of security in computing. One focuses mainly on external threats, and generally treats the computer system itself as a trusted system. See the article computer insecurity for a description of the current state of the art in this approach.

Computer security by design

The other regards the computer system itself as largely an untrusted system, and redesigns it to make it more secure in a number of ways.

This technique enforces privilege separation, where an entity has only the privileges that are needed for its function. That way, even if an attacker has subverted one part of the system, fine-grained security ensures that it is just as difficult for them to subvert the rest.

Futhermore, by breaking the system up into smaller components, the complexity of individual components is reduced, opening up the possibility of using techniques such as automated theorem proving to prove the correctness of crucial software subsystems. Where formal correctness proofs are not possible, rigorous use of code review and unit testing measures can be used to try to make modules as secure as possible.

The design should use "defense in depth", where more than one subsystem needs to be compromised to compromise the security of the system and the information it holds. Subsystems should default to secure settings, and wherever possible should be designed to "fail secure" rather than "fail insecure" (see fail safe for the equivalent in safety engineering). Ideally, a secure system should require a deliberate, conscious, knowledgeable and free decision on the part of legitimate authorities in order to make it insecure.

In addition, security should not be an all-or-nothing issue. The designers and operators of systems should assume that security breaches are inevitable in the long term. Full audit trails should be kept of system activity, so that when a security breach occurs, the mechanism and extent of the breach can be determined. Finally, full disclosure helps to ensure that when bugs are found the "window of vulnerability" is kept as short as possible.

Early history of security by design

The early Multics operating system was notable for its early emphasis on computer security by design, and Multics was possibly the very first operating system to be designed as a secure system from the ground up. In spite of this, Multics security was broken, not once, but repeatedly. This led to further work on computer security that prefigured modern security engineering techniques.

Techniques for creating secure systems

The following techniques can be used in engineering secure systems. Note that these techniques, whilst useful, do not of themselves ensure security -- a security system is no stronger than its weakest link.

Cryptographic techniques can be used to defend data in transit between systems, reducing the probability that data exchanged between systems can be intercepted or modified.

Strong authentication techniques can be used to ensure that communication end-points are who they say they are.

Secure cryptoprocessors can be used to leverage physical security techniques into protecting the security of the computer system.

Chain of trust techniques can be used to attempt to ensure that all software loaded has been certified as authentic by the system's designers.

Mandatory access control can be used to ensure that privileged access is withdrawn when privileges are revoked. For example, deleting a user account should also stop any processes that are running with that user's privileges.

Capability and access control list techniques can be used to ensure privilege separation and mandatory access control. The next sections discuss their use.

Capabilities vs. ACLs

Within computer systems, the two fundamental means of enforcing privilege separation are access control lists (ACLs) and capabilities. The semantics of ACLs have been proven to be insecure in many situations (e.g., Confused Deputy Problem). It has also been shown that ACL's promise of giving access to an object to only one person can never be guaranteed in practice. Both of these problems are resolved by capabilities.

Unfortunately, for various historical reasons, capabilities have been restricted to research operating systems and commercial OSes still use ACLs.

The Cambridge CAP computer demonstrated the use of capabilities, both in hardware and software, in the 1970s, so this technology is hardly new. A reason for the lack of adoption of capabilities may be that ACLs appeared to offer a 'quick fix' for security without pervasive redesign of the operating system and hardware.

A good example of a current secure system is Eros.

Further reading

Computer security is a highly complex field, and it is relatively immature. The ever-greater amounts of money dependent on electronic information make protecting it a growing industry and an active research topic.

See also: security engineering, authentication, cryptology, cryptography, physical security, hacking, cracking, shellcodes, electronic underground community, Defensive programming, full disclosure, INFOSEC, COMSEC

References:

• Ross J. Anderson, Security Engineering: A Guide to Building Dependable Distributed Systems, ISBN 0471389226
• Bruce Schneier, Secrets & Lies: Digital Security in a Networked World, ISBN 0471253111
• David A. Wheeler, Secure Programming for Linux and Unix HOWTO (GFDL License)
• Paul A. Karger, Roger R. Schell. Thirty Years Later: Lessons from the Multics Security Evaluation. IBM white paper.

• Computer Security Fact Forum Framework
• Intro to Caps
• ACLs vs. Caps
• Intro to Cap Security
• Why aren't Caps and ACLs equivalent?
• Open Source Distributed Capabilities
• REST and capability-based security
• The Cambridge CAP capability-based computer architecture
• Online book: "Capability-Based Computer Systems" by Henry M. Levy
• Henry M. Levy - Capability-Based Computer Systems. Digital Press, Bedford, Massachusetts, 1984, ISBN 0932376223 (out of print -- text available online on author's website)

  Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Secure computing."

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Abbreviations & Acronyms: Computer

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Synonyms within Context: Computer

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Modern Usage: Computer

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Commercial Usage: Computer

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Image Slideshow: Computer

Photos: Computer More pictures...

Illustrations: Computer More pictures...

Computer Images: Computer More pictures...

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Photo Album: Computer

Thumbnail	Description & Credit	Thumbnail	Description & Credit
	Shown is a computer graphic of tgf-beta molecule. Tgf-beta belongs to a superfamily of fetal inducers and regressors, which signal specific patterns of cellular differentiation. Tgf-beta, a cytokine with three different isoforms, regulates many cellular functions including cell proliferation, differentiation, adhesion and migration. Four novel receptors were characterized that also act as serine/threonine kinases and one of these appears to be a tgf-beta receptor. Credit: Unknown photographer/artist.		DNA microarray technology is a powerful new research tool that allows scientists to assess the level of expression of a large subset of the 100,000 human genes in a cell or tissue. This technology can quickly produce a snapshot of the genes that are active in a tumor cell, critical information in narrowing the precise molecular causes of a cancer. Two different images available. First is of female lab technician sitting at computer that displays a microarray. The second is a man at same setting. Credit: Bill Branson.
	CDC employee working at computer. Credit: CDC.		New Animation Depicts Changs in Antarctic Ice Sheet For the first time, scientists at NASA have generated a computer model depicting changes in the Antarctic ice sheet since the peak of the last ice age - nearly 20,000 years ago. The West Antarctic ice. Credit: NASA.
	X-4 with "Female Computer". Credit: NASA.		Female Computer. Credit: NASA.
	Imagine turning your home computer into the equivalent of a professional telescope which can ... Credit: NASA.		Computer generated surface view of a corona, tentatively named Idem-Kuva. Credit: NASA.
	Computer rendering of Triton's surface. Credit: NASA.		Maria Mitchell Worked under contract to the Coast Survey in mid-1840's First woman professional to work for the Federal Government Famous astronomer, computer for the Nautical Almanac, professor at Vassar. Credit: Coast & Geodetic Survey Historical Image Collection.
Source: pictures compiled by the editor from various references; see picture credits.

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Digital Photo Gallery: Computer
 

"Laptop Computer" by Stacy Taylor Commentary: "Laptop I took a pic of for a brochure I'm working on."	"Computer" by Jef T Commentary: "I made this computer using 3D Studio Max. It was for an advertisment for Blogger.com."
Source: photographs selected by the editor, with permission from the photographers.

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Sounds Captioned with "Computer".

Play	Caption
	Synthesized ambient music with computer tones.
Source: compiled by the editor from various references; see credits.

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Familiar Quotations: Computer

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Use in Literature: Computer

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Non-Fiction Usage: Computer

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Spoken Usage: Computer

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Speeches: Computer

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Usage Frequency: Computer

Source: compiled by the editor from several corpora; see credits.

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Usage in Company Names: Computer

Source: compiled by the editor from Icon Group International, Inc.

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Expressions: Computer

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Frequency of Internet Keywords: Computer

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Modern Translation: Computer

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Ancestral Language Translations: Computer

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Derivations & Misspellings: Computer

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Rhyming with "Computer"

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Anagrams: Computer

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