1.
Calculator
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An electronic calculator is a small, portable electronic device used to perform operations ranging from basic arithmetic to complex mathematics. The first solid state electronic calculator was created in the 1960s, building on the history of tools such as the abacus. It was developed in parallel with the computers of the day. The pocket sized devices became available in the 1970s, especially after the first microprocessor and they later became used commonly within the petroleum industry. Modern electronic calculators vary, from cheap, give-away, credit-card-sized models to sturdy desktop models with built-in printers and they became popular in the mid-1970s. By the end of decade, calculator prices had reduced to a point where a basic calculator was affordable to most. In addition to general purpose calculators, there are designed for specific markets. For example, there are scientific calculators which include trigonometric and statistical calculations, some calculators even have the ability to do computer algebra. Graphing calculators can be used to graph functions defined on the real line, as of 2016, basic calculators cost little, but the scientific and graphing models tend to cost more. In 1986, calculators still represented an estimated 41% of the worlds general-purpose hardware capacity to compute information, by 2007, this diminished to less than 0. 05%. Modern 2016 electronic calculators contain a keyboard with buttons for digits and arithmetical operations, most basic calculators assign only one digit or operation on each button, however, in more specific calculators, a button can perform multi-function working with key combinations. Large-sized figures and comma separators are used to improve readability. Various symbols for function commands may also be shown on the display, fractions such as 1⁄3 are displayed as decimal approximations, for example rounded to 0.33333333. Also, some fractions can be difficult to recognize in decimal form, as a result, Calculators also have the ability to store numbers into computer memory. Basic types of these only one number at a time. The variables can also be used for constructing formulas, some models have the ability to extend memory capacity to store more numbers, the extended memory address is termed an array index. Power sources of calculators are, batteries, solar cells or mains electricity, some models even have no turn-off button but they provide some way to put off. Crank-powered calculators were also common in the computer era
2.
Computer science
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Computer science is the study of the theory, experimentation, and engineering that form the basis for the design and use of computers. An alternate, more succinct definition of science is the study of automating algorithmic processes that scale. A computer scientist specializes in the theory of computation and the design of computational systems and its fields can be divided into a variety of theoretical and practical disciplines. Some fields, such as computational complexity theory, are highly abstract, other fields still focus on challenges in implementing computation. Human–computer interaction considers the challenges in making computers and computations useful, usable, the earliest foundations of what would become computer science predate the invention of the modern digital computer. Machines for calculating fixed numerical tasks such as the abacus have existed since antiquity, further, algorithms for performing computations have existed since antiquity, even before the development of sophisticated computing equipment. Wilhelm Schickard designed and constructed the first working mechanical calculator in 1623, in 1673, Gottfried Leibniz demonstrated a digital mechanical calculator, called the Stepped Reckoner. He may be considered the first computer scientist and information theorist, for, among other reasons and he started developing this machine in 1834, and in less than two years, he had sketched out many of the salient features of the modern computer. A crucial step was the adoption of a card system derived from the Jacquard loom making it infinitely programmable. Around 1885, Herman Hollerith invented the tabulator, which used punched cards to process statistical information, when the machine was finished, some hailed it as Babbages dream come true. During the 1940s, as new and more powerful computing machines were developed, as it became clear that computers could be used for more than just mathematical calculations, the field of computer science broadened to study computation in general. Computer science began to be established as an academic discipline in the 1950s. The worlds first computer science program, the Cambridge Diploma in Computer Science. The first computer science program in the United States was formed at Purdue University in 1962. Since practical computers became available, many applications of computing have become distinct areas of study in their own rights and it is the now well-known IBM brand that formed part of the computer science revolution during this time. IBM released the IBM704 and later the IBM709 computers, still, working with the IBM was frustrating if you had misplaced as much as one letter in one instruction, the program would crash, and you would have to start the whole process over again. During the late 1950s, the science discipline was very much in its developmental stages. Time has seen significant improvements in the usability and effectiveness of computing technology, modern society has seen a significant shift in the users of computer technology, from usage only by experts and professionals, to a near-ubiquitous user base
3.
Graphical user interface
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GUIs were introduced in reaction to the perceived steep learning curve of command-line interfaces, which require commands to be typed on a computer keyboard. The actions in a GUI are usually performed through direct manipulation of the graphical elements, beyond computers, GUIs are used in many handheld mobile devices such as MP3 players, portable media players, gaming devices, smartphones and smaller household, office and industrial controls. Designing the visual composition and temporal behavior of a GUI is an important part of application programming in the area of human–computer interaction. Its goal is to enhance the efficiency and ease of use for the logical design of a stored program. Methods of user-centered design are used to ensure that the language introduced in the design is well-tailored to the tasks. The visible graphical interface features of an application are sometimes referred to as chrome or GUI, typically, users interact with information by manipulating visual widgets that allow for interactions appropriate to the kind of data they hold. The widgets of an interface are selected to support the actions necessary to achieve the goals of users. A model–view–controller allows a structure in which the interface is independent from and indirectly linked to application functions. This allows users to select or design a different skin at will, good user interface design relates to users more, and to system architecture less. Large widgets, such as windows, usually provide a frame or container for the main presentation content such as a web page, smaller ones usually act as a user-input tool. A GUI may be designed for the requirements of a market as application-specific graphical user interfaces. By the 1990s, cell phones and handheld game systems also employed application specific touchscreen GUIs, newer automobiles use GUIs in their navigation systems and multimedia centers, or navigation multimedia center combinations. Sample graphical desktop environments A GUI uses a combination of technologies and devices to provide a platform that users can interact with, a series of elements conforming a visual language have evolved to represent information stored in computers. This makes it easier for people with few computer skills to work with, the most common combination of such elements in GUIs is the windows, icons, menus, pointer paradigm, especially in personal computers. The WIMP style of interaction uses a virtual device to represent the position of a pointing device, most often a mouse. Available commands are compiled together in menus, and actions are performed making gestures with the pointing device, a window manager facilitates the interactions between windows, applications, and the windowing system. The windowing system handles hardware devices such as pointing devices, graphics hardware, window managers and other software combine to simulate the desktop environment with varying degrees of realism. Smaller mobile devices such as personal assistants and smartphones typically use the WIMP elements with different unifying metaphors, due to constraints in space
4.
Dialog box
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The graphical control element dialog box is a small window that communicates information to the user and prompts them for a response. Dialog boxes are classified as modal or modeless, depending on whether they block interaction with the software that initiated the dialog, the type of dialog box displayed is dependent upon the desired user interaction. An example of a box is the about box found in many software programs, which usually displays the name of the program, its version number. Non-modal or modeless dialog boxes are used when the information is not essential to continue. In general, good software design calls for dialogs to be of this type where possible, an example might be a dialog of settings for the current document, e. g. the background and text colors. The user can continue adding text to the main window whatever color it is, usability practitioners generally regard modal dialogs as bad design-solutions, since they are prone to produce mode errors. Dangerous actions should be undoable wherever possible, a modal alert dialog that appears unexpectedly or which is dismissed automatically will not protect from the dangerous action, a modal dialog interrupts the main workflow. This effect has either been sought by the developer because it focuses on the completion of the task at hand or rejected because it prevents the user from changing to a different task when needed. The concept of a document modal dialog has recently used, most notably in OS X. In the first case, they are shown as sheets attached to a parent window and these dialogs block only that window until the user dismisses the dialog, permitting work in other windows to continue, even within the same application. In OS X, dialogs appear to emanate from a slot in their parent window and this helps to let the user understand that the dialog is attached to the parent window, not just shown in front of it. The OS X dialog box blocks the parent window, preventing the user from referring to it while interacting with the dialog and this may require the user to close the dialog to access the necessary information, then re-open the dialog box to continue
5.
Hard disk drive
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The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a manner, meaning that individual blocks of data can be stored or retrieved in any order. HDDs are a type of storage, retaining stored data even when powered off. Introduced by IBM in 1956, HDDs became the dominant secondary storage device for computers by the early 1960s. Continuously improved, HDDs have maintained this position into the era of servers. More than 200 companies have produced HDDs historically, though after extensive industry consolidation most current units are manufactured by Seagate, Toshiba, as of 2016, HDD production is growing, although unit shipments and sales revenues are declining. While SSDs have higher cost per bit, SSDs are replacing HDDs where speed, power consumption, small size, the primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000, the two most common form factors for modern HDDs are 3. 5-inch, for desktop computers, and 2. 5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA, SATA, Hard disk drives were introduced in 1956, as data storage for an IBM real-time transaction processing computer and were developed for use with general-purpose mainframe and minicomputers. The first IBM drive, the 350 RAMAC in 1956, was approximately the size of two medium-sized refrigerators and stored five million six-bit characters on a stack of 50 disks. In 1962 the IBM350 RAMAC disk storage unit was superseded by the IBM1301 disk storage unit, cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches above the platter surface. Motion of the head array depended upon a binary system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes, access time was about a quarter of a second. Also in 1962, IBM introduced the model 1311 disk drive, users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations, non-removable HDDs were called fixed disk drives. Some high-performance HDDs were manufactured with one head per track so that no time was lost physically moving the heads to a track, known as fixed-head or head-per-track disk drives they were very expensive and are no longer in production. In 1973, IBM introduced a new type of HDD code-named Winchester and its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Instead, the heads were allowed to land on an area of the disk surface upon spin-down
6.
Operating system
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An operating system is system software that manages computer hardware and software resources and provides common services for computer programs. All computer programs, excluding firmware, require a system to function. Operating systems are found on many devices that contain a computer – from cellular phones, the dominant desktop operating system is Microsoft Windows with a market share of around 83. 3%. MacOS by Apple Inc. is in place, and the varieties of Linux is in third position. Linux distributions are dominant in the server and supercomputing sectors, other specialized classes of operating systems, such as embedded and real-time systems, exist for many applications. A single-tasking system can run one program at a time. Multi-tasking may be characterized in preemptive and co-operative types, in preemptive multitasking, the operating system slices the CPU time and dedicates a slot to each of the programs. Unix-like operating systems, e. g. Solaris, Linux, cooperative multitasking is achieved by relying on each process to provide time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking, 32-bit versions of both Windows NT and Win9x, used preemptive multi-tasking. Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem, a distributed operating system manages a group of distinct computers and makes them appear to be a single computer. The development of networked computers that could be linked and communicate with each other gave rise to distributed computing, distributed computations are carried out on more than one machine. When computers in a work in cooperation, they form a distributed system. The technique is used both in virtualization and cloud computing management, and is common in large server warehouses, embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines like PDAs with less autonomy and they are able to operate with a limited number of resources. They are very compact and extremely efficient by design, Windows CE and Minix 3 are some examples of embedded operating systems. A real-time operating system is a system that guarantees to process events or data by a specific moment in time. A real-time operating system may be single- or multi-tasking, but when multitasking, early computers were built to perform a series of single tasks, like a calculator. Basic operating system features were developed in the 1950s, such as resident monitor functions that could run different programs in succession to speed up processing
7.
Personal computer hardware
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Computer hardware is the collection of physical components that constitute a computer system. By contrast, software is instructions that can be stored and run by hardware, hardware is directed by the software to execute any command or instruction. A combination of hardware and software forms a usable computing system, the template for all modern computers is the Von Neumann architecture, detailed in a 1945 paper by Hungarian mathematician John von Neumann. The meaning of the term has evolved to mean a stored-program computer in which an instruction fetch and this is referred to as the Von Neumann bottleneck and often limits the performance of the system. For the third year, U. S. business-to-business channel sales increased. The impressive growth was the fastest sales increase since the end of the recession, sales growth accelerated in the second half of the year peaking in fourth quarter with a 6.9 percent increase over the fourth quarter of 2012. There are a number of different types of system in use today. The personal computer, also known as the PC, is one of the most common types of computer due to its versatility, laptops are generally very similar, although they may use lower-power or reduced size components, thus lower performance. The computer case is a plastic or metal enclosure that houses most of the components, a case can be either big or small, but the form factor of motherboard for which it is designed matters more. A power supply unit converts alternating current electric power to low-voltage DC power for the components of the computer. Laptops are capable of running from a battery, normally for a period of hours. The motherboard is the component of a computer. It is usually cooled by a heatsink and fan, or water-cooling system, most newer CPUs include an on-die Graphics Processing Unit. The clock speed of CPUs governs how fast it executes instructions, many modern computers have the option to overclock the CPU which enhances performance at the expense of greater thermal output and thus a need for improved cooling. The chipset, which includes the bridge, mediates communication between the CPU and the other components of the system, including main memory. Random-Access Memory, which stores the code and data that are being accessed by the CPU. For example, when a web browser is opened on the computer it takes up memory, RAM usually comes on DIMMs in the sizes 2GB, 4GB, and 8GB, but can be much larger. Read-Only Memory, which stores the BIOS that runs when the computer is powered on or otherwise begins execution, the BIOS includes boot firmware and power management firmware
8.
Usability
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Usability is the ease of use and learnability of a human-made object such as a tool or device. The object of use can be an application, website, book, tool, machine, process, vehicle. A usability study may be conducted as a job function by a usability analyst or as a secondary job function by designers, technical writers, marketing personnel. It is widely used in electronics, communication, and knowledge transfer objects. Usability includes methods of measuring usability, such as needs analysis, in human-computer interaction and computer science, usability studies the elegance and clarity with which the interaction with a computer program or a web site is designed. Usability differs from user satisfaction and user experience because usability does not directly consider usefulness or utility, by understanding and researching the interaction between product and user, the usability expert can also provide insight that is unattainable by traditional company-oriented market research. For example, after observing and interviewing users, the usability expert may identify needed functionality or design flaws that were not anticipated, a method called contextual inquiry does this in the naturally occurring context of the users own environment. In the user-centered design paradigm, the product is designed with its users in mind at all times. In the user-driven or participatory design paradigm, some of the users become actual or de facto members of the design team, the term user friendly is often used as a synonym for usable, though it may also refer to accessibility. Usability describes the quality of experience across websites, software, products. There is no consensus about the relation of the terms ergonomics, some think of usability as the software specialization of the larger topic of ergonomics. Others view these topics as tangential, with focusing on physiological matters. Usability is also important in website development, according to Jakob Nielsen, Studies of user behavior on the Web find a low tolerance for difficult designs or slow sites. And they dont want to learn how to use a home page, theres no such thing as a training class or a manual for a Web site. People have to be able to grasp the functioning of the immediately after scanning the home page—for a few seconds at most. Otherwise, most casual users simply leave the site and browse or shop elsewhere, ISO defines usability as The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use. The word usability also refers to methods for improving ease-of-use during the design process, efficiency, Once users have learned the design, how quickly can they perform tasks. Memorability, When users return to the design after a period of not using it, errors, How many errors do users make, how severe are these errors, and how easily can they recover from the errors
9.
Floppy disk
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Floppy disks are read and written by a floppy disk drive. Floppy disks, initially as 8-inch media and later in 5¼-inch and 3½-inch sizes, were a form of data storage and exchange from the mid-1970s into the mid-2000s. These formats are usually handled by older equipment and these disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation. The term floppy disk appeared in print as early as 1970, in 1976, Shugart Associates introduced the first 5¼-inch FDD. By 1978 there were more than 10 manufacturers producing such FDDs, there were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as FM, MFM and GCR. The 5¼-inch format displaced the 8-inch one for most applications, the most common capacity of the 5¼-inch format in DOS-based PCs was 360 kB and in 1984 IBM introduced the 1.2 MB dual-sided floppy disk along with its PC-AT model. IBM started using the 720 kB double-density 3½-inch microfloppy disk on its Convertible laptop computer in 1986 and these disk drives could be added to older PC models. In 1988 IBM introduced a drive for 2.88 MB DSED diskettes in its top-of-the-line PS/2 models, throughout the early 1980s, limitations of the 5¼-inch format became clear. Originally designed to be practical than the 8-inch format, it was itself too large, as the quality of recording media grew. A number of solutions were developed, with drives at 2-, 2½-, 3-, 3½-, the large market share of the 5¼-inch format made it difficult for these new formats to gain significant market share. A variant on the Sony design, introduced in 1982 by a number of manufacturers, was then rapidly adopted. By the end of the 1980s, 5¼-inch disks had been superseded by 3½-inch disks, by the mid-1990s, 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant floppy disk. Floppy disks became ubiquitous during the 1980s and 1990s in their use with computers to distribute software, transfer data. Before hard disks became affordable to the population, floppy disks were often used to store a computers operating system. Most home computers from that period have a primary OS and BASIC stored as ROM, by the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were a five billion standard floppy disks in use. Then, distribution of packages was gradually replaced by CD-ROMs, DVDs. External USB-based floppy disk drives are available, many modern systems provide firmware support for booting from such drives
10.
Software bug
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A software bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. Most bugs arise from mistakes and errors made in either a source code or its design, or in components. A few are caused by compilers producing incorrect code, a program that contains a large number of bugs, and/or bugs that seriously interfere with its functionality, is said to be buggy. Bugs trigger errors that may have ripple effects, Bugs may have subtle effects or cause the program to crash or freeze the computer. Others qualify as security bugs and might, for example, enable a user to bypass access controls in order to obtain unauthorized privileges. Bugs in code that controls the Therac-25 radiation therapy machine were directly responsible for patient deaths in the 1980s. In 1996, the European Space Agencys US$1 billion prototype Ariane 5 rocket had to be destroyed less than a minute after launch due to a bug in the guidance computer program. In June 1994, a Royal Air Force Chinook helicopter crashed into the Mull of Kintyre, for instance, Thomas Edison wrote the following words in a letter to an associate in 1878, It has been just so in all of my inventions. The Middle English word bugge is the basis for the terms bugbear and bugaboo, baffle Ball, the first mechanical pinball game, was advertised as being free of bugs in 1931. Problems with military gear during World War II were referred to as bugs, isaac Asimov uses the term bug to relate to issues with a robot in his short story Catch That Rabbit, published in 1944, and included in his well-known collection of short stories I, Robot. From page 1 of Catch That Rabbit, U. S, robots had to get the bugs out of the multiple robot, and there were plenty of bugs, and there are always at least half a dozen bugs left for the field-testing. The term bug was used in an account by computer pioneer Grace Hopper, operators traced an error in the Mark II to a moth trapped in a relay, coining the term bug. This bug was carefully removed and taped to the log book, stemming from the first bug, today we call errors or glitches in a program a bug. Hopper did not find the bug, as she readily acknowledged, the date in the log book was September 9,1947. Hopper loved to recount the story and this log book, complete with attached moth, is part of the collection of the Smithsonian National Museum of American History. The related term debug also appears to predate its usage in computing, an analysing process must equally have been performed in order to furnish the Analytical Engine with the necessary operative data, and that herein may also lie a possible source of error. Granted that the mechanism is unerring in its processes, the cards may give it wrong orders. The report highlights the need for reform in the field of software vulnerability discovery, government researchers, companies, and cyber security experts are the people who typically discover software flaws
11.
Command-line interface
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A program which handles the interface is called a command language interpreter or shell. The interface is implemented with a command line shell, which is a program that accepts commands as text input. Command-line interfaces to computer operating systems are widely used by casual computer users. Alternatives to the line include, but are not limited to text user interface menus, keyboard shortcuts. Examples of this include the Windows versions 1,2,3,3.1, and 3.11, DosShell, and Mouse Systems PowerPanel. Command-line interfaces are preferred by more advanced computer users, as they often provide a more concise. Programs with command-line interfaces are generally easier to automate via scripting, a program that implements such a text interface is often called a command-line interpreter, command processor or shell. Under most operating systems, it is possible to replace the shell program with alternatives, examples include 4DOS for DOS, 4OS2 for OS/2. For example, the default Windows GUI is a program named EXPLORER. EXE. These programs are shells, but not CLIs, application programs may also have command line interfaces. When a program is launched from an OS command line shell, interactive command line sessions, After launch, a program may provide an operator with an independent means to enter commands in the form of text. OS inter-process communication, Most operating systems support means of inter-process communication, Command lines from client processes may be redirected to a CLI program by one of these methods. Some applications support only a CLI, presenting a CLI prompt to the user, Some examples of CLI-only applications are, DEBUG Diskpart Ed Edlin Fdisk Ping Some computer programs support both a CLI and a GUI. In some cases, a GUI is simply a wrapper around a separate CLI executable file, in other cases, a program may provide a CLI as an optional alternative to its GUI. CLIs and GUIs often support different functionality, for example, all features of MATLAB, a numerical analysis computer program, are available via the CLI, whereas the MATLAB GUI exposes only a subset of features. The early Sierra games, like the first three Kings Quest games, used commands from a command line to move the character around in the graphic window. Early computer systems often used teleprinter machines as the means of interaction with a human operator, the computer became one end of the human-to-human teleprinter model. So instead of a human communicating with another human over a teleprinter, in time, the actual mechanical teleprinter was replaced by a glass tty, and then by a smart terminal
12.
Icon (computing)
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In computing, an icon is a pictogram or ideogram displayed on a computer screen in order to help the user navigate a computer system or mobile device. It can serve as an electronic hyperlink or file shortcut to access the program or data, the user can activate an icon using a mouse, pointer, finger, or recently voice commands. Their placement on the screen, also in relation to other icons, in activating an icon, the user can move directly into and out of the identified function without knowing anything further about the location or requirements of the file or code. Graphically, the icon is a picture of objects that users are familiar with from office environment or from other professional arenas. One group of icons was taken from the symbols found across all devices, such as the power on/off symbol. Another group is metaphorically representing desktop objects from the 1980s office environment, a third group of icons are the brand icons used to identify commercial software programs. These commercial icons serve as links on the system to the program or data files created by a specific software provider. Although icons are depicted in graphical user interfaces, icons are sometimes rendered in a TUI using special characters such as MouseText or PETSCII. The design of all computer icons is constricted by the limitations of the device display and they are limited in size, with the standard size about a thumbnail for both desktop computer systems and mobile devices. They are frequently scalable, as they are displayed in different positions in the software, the colors used, of both the image and the icon background, should stand out on different system backgrounds. The detailing of the image needs to be simple, remaining recognizable in varying graphical resolutions. Computer icons are by definition language-independent, they do not rely on letters or words to convey their meaning and these visual parameters place rigid limits on the design of icons, frequently requiring the skills of a graphic artist in their development. Because of their size and versatility, computer icons have become a mainstay of user interaction with electronic media. Icons also provide rapid entry into the system functionality, on most systems, users can create and delete, replicate, select, click or double-click standard computer icons and drag them to new positions on the screen to create a customized user environment. Some common computer icons are taken from the field of standardized icons used across a wide range of electrical equipment. Examples of these are the symbol and the USB icon. The standardization of electronic icons is an important safety-feature on all types of electronics, as a subset of electronic devices, computer systems and mobile devices use many of the same icons, they are incorporated into the design of both the computer hardware and on the software. On the hardware, these identify the functionality of specific buttons
13.
Virtual memory
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In computing, virtual memory is a memory management technique that is implemented using both hardware and software. It maps memory addresses used by a program, called virtual addresses, main storage as seen by a process or task appears as a contiguous address space or collection of contiguous segments. The operating system virtual address spaces and the assignment of real memory to virtual memory. Address translation hardware in the CPU, often referred to as a management unit or MMU. Memory virtualization can be considered a generalization of the concept of virtual memory, virtual memory is an integral part of a modern computer architecture, implementations usually require hardware support, typically in the form of a memory management unit built into the CPU. While not necessary, emulators and virtual machines can employ hardware support to increase performance of their virtual memory implementations, during the 1960s and early 70s, computer memory was very expensive. The introduction of virtual memory provided an ability for software systems with large memory demands to run on computers with less real memory, the savings from this provided a strong incentive to switch to virtual memory for all systems. The additional capability of providing virtual address spaces added another level of security and reliability, most modern operating systems that support virtual memory also run each process in its own dedicated address space. Each program thus appears to have access to the virtual memory. However, some operating systems and even modern ones are single address space operating systems that run all processes in a single address space composed of virtualized memory. This is because embedded hardware costs are kept low by implementing all such operations with software rather than with dedicated hardware. In the 1940s and 1950s, all larger programs had to contain logic for managing primary and secondary storage, virtual memory was therefore introduced not only to extend primary memory, but to make such an extension as easy as possible for programmers to use. To allow for multiprogramming and multitasking, many early systems divided memory between multiple programs without virtual memory, such as models of the PDP-10 via registers. The first Atlas was commissioned in 1962 but working prototypes of paging had been developed by 1959, in 1961, the Burroughs Corporation independently released the first commercial computer with virtual memory, the B5000, with segmentation rather than paging. Before virtual memory could be implemented in operating systems, many problems had to be addressed. Dynamic address translation required expensive and difficult to build specialized hardware, there were worries that new system-wide algorithms utilizing secondary storage would be less effective than previously used application-specific algorithms. The first minicomputer to introduce virtual memory was the Norwegian NORD-1, during the 1970s, other minicomputers implemented virtual memory, virtual memory was introduced to the x86 architecture with the protected mode of the Intel 80286 processor, but its segment swapping technique scaled poorly to larger segment sizes. The Intel 80386 introduced paging support underneath the existing segmentation layer, however, loading segment descriptors was an expensive operation, causing operating system designers to rely strictly on paging rather than a combination of paging and segmentation
14.
Out of memory
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Out of memory is an often undesired state of computer operation where no additional memory can be allocated for use by programs or the operating system. Such a system will be unable to load any additional programs, and since many programs may load additional data into memory during execution and this usually occurs because all available memory, including disk swap space, has been allocated. Since the advent of virtual memory opened the door for the usage of swap space, therefore, they would either fail immediately with an out of memory error message, or work as expected. Early operating systems such as MS-DOS lacked support for multitasking, programs were allocated physical memory that they could use as they needed. Modern operating systems provide virtual memory, in processes are given a range of memory. Virtual memory can be backed by physical RAM, a file via mmap, or swap space. Because virtual memory does not need to be backed by physical memory, exhaustion of it is rare, and usually there are other limits imposed by the operating system on resource consumption. As predicted by Moores law, the amount of memory in all computers has grown almost exponentially, although this is offset to some degree by programs. This condition, known as thrashing, usually renders the computer unusable until some programs are closed or the machine is rebooted, due to these reasons, an out of memory message is rarely encountered by applications with modern computers. It is, however, still possible to encounter an OOM condition with a modern computer, the typical OOM case in modern computers happens when the operating system is unable to create any more virtual memory, because all of its potential backing devices have been filled. Operating systems kernels such as Linux will attempt to recover from this type of OOM condition by terminating one or more processes, Linux 4.6 released on May 2016 introduced changes in OOM situations improving detection and reliability. Apart from the physical memory limits, some systems limit the amount of memory each process can use. Usually a matter of policy, such a limitation can also happen when the OS has an address space than is available at the process level. Some high-end 32-bit systems come with 8 gigabytes or more of system memory, a process which exceeds its per-process limit and then attempts to allocate further memory will encounter an error condition. For example, the C standard function for allocating memory, malloc, a well-behaved application should handle this situation gracefully, however, many do not
15.
Random-access memory
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Random-access memory is a form of computer data storage which stores frequently used program instructions to increase the general speed of a system. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the location of data inside the memory. RAM contains multiplexing and demultiplexing circuitry, to connect the lines to the addressed storage for reading or writing the entry. Usually more than one bit of storage is accessed by the same address, in todays technology, random-access memory takes the form of integrated circuits. RAM is normally associated with types of memory, where stored information is lost if power is removed. Other types of non-volatile memories exist that allow access for read operations. These include most types of ROM and a type of memory called NOR-Flash. Integrated-circuit RAM chips came into the market in the early 1970s, with the first commercially available DRAM chip, early computers used relays, mechanical counters or delay lines for main memory functions. Ultrasonic delay lines could only reproduce data in the order it was written, drum memory could be expanded at relatively low cost but efficient retrieval of memory items required knowledge of the physical layout of the drum to optimize speed. Latches built out of vacuum tube triodes, and later, out of transistors, were used for smaller and faster memories such as registers. Such registers were relatively large and too costly to use for large amounts of data, the first practical form of random-access memory was the Williams tube starting in 1947. It stored data as electrically charged spots on the face of a cathode ray tube, since the electron beam of the CRT could read and write the spots on the tube in any order, memory was random access. The capacity of the Williams tube was a few hundred to around a thousand bits, but it was smaller, faster. In fact, rather than the Williams tube memory being designed for the SSEM, magnetic-core memory was invented in 1947 and developed up until the mid-1970s. It became a form of random-access memory, relying on an array of magnetized rings. By changing the sense of each rings magnetization, data could be stored with one bit stored per ring, since every ring had a combination of address wires to select and read or write it, access to any memory location in any sequence was possible. Magnetic core memory was the form of memory system until displaced by solid-state memory in integrated circuits. Data was stored in the capacitance of each transistor, and had to be periodically refreshed every few milliseconds before the charge could leak away
16.
Windows XP
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Windows XP is a personal computer operating system that was produced by Microsoft as part of the Windows NT family of operating systems. It was released to manufacturing on August 24,2001, however, in January 2000, both projects were shelved in favor of a single OS codenamed Whistler, which would serve as a single OS platform for both consumer and business markets. Windows XP was an advance from the MS-DOS based versions of Windows in security, stability. It introduced a significantly redesigned graphical user interface and was the first version of Windows to use product activation in an effort to reduce its copyright infringement. Despite some initial concerns over the new licensing model and product activation system, Windows XP eventually proved to be popular and widely used. It is estimated that at least 400 million copies of Windows XP were sold globally within its first five years of availability, sales of Windows XP licenses to original equipment manufacturers ceased on June 30,2008, but continued for netbooks until October 2010. Windows XP remained popular even after the release of newer versions, vistas 2009 successor, Windows 7, only overtook XP in total market share at the end of 2011. Extended support for Windows XP ended on April 8,2014, as of November 2016, Windows XP desktop market share makes it the fourth most popular Windows version after Windows 7, Windows 10 and Windows 8.1. Windows XP is still popular in some countries, Africa as a whole and in Asia, e. g. in China. A number of activity centers were planned, serving as hubs for email communications, playing music, managing or viewing photos, searching the Internet, however, the project proved to be too ambitious. Microsoft discussed a plan to delay Neptune in favor of an interim OS known as Asteroid, which would have been an update to Windows 2000, and since Neptune and Odyssey would be based on the same code-base anyway, it made sense to combine them into a single project. In June 2000, Microsoft began the technical beta testing process, Whistler was expected to be available in Personal, Professional, Server, Advanced Server. At PDC on July 13,2000, Microsoft announced that Whistler would be released during the half of 2001. Build 2257 featured further refinements to the Watercolor theme, along with the introduction of the two-column Start menu. Microsoft released Whistler Beta 1, build 2296, on October 31,2000, build 2410 in January 2001 introduced Internet Explorer 6.0 and the Microsoft Product Activation system. Making it very friendly for the user to use. Builds 2416 and 2419 added the File and Transfer Settings Wizard, on February 5,2001, Microsoft officially announced that Whistler would be known as Windows XP, where XP stands for experience. As a complement, the version of Microsoft Office was also announced as Office XP
17.
Windows 7
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Windows 7 is a personal computer operating system developed by Microsoft. It is a part of the Windows NT family of operating systems, Windows 7 was released to manufacturing on July 22,2009, and became generally available on October 22,2009, less than three years after the release of its predecessor, Windows Vista. Windows 7s server counterpart, Windows Server 2008 R2, was released at the same time, Windows 7 continued improvements on Windows Aero with the addition of a redesigned taskbar that allows applications to be pinned to it, and new window management features. Other new features were added to the system, including libraries, the new file sharing system HomeGroup. A new Action Center interface was added to provide an overview of system security and maintenance information. Windows 7 also shipped with updated versions of several applications, including Internet Explorer 8, Windows Media Player. Windows 7 was a success for Microsoft, even prior to its official release. Originally, a version of Windows codenamed Blackcomb was planned as the successor to Windows XP, major features were planned for Blackcomb, including an emphasis on searching and querying data and an advanced storage system named WinFS to enable such scenarios. However, an interim, minor release, codenamed Longhorn, was announced for 2003, by the middle of 2003, however, Longhorn had acquired some of the features originally intended for Blackcomb. Development of Longhorn was also restarted, and thus delayed, in August 2004, a number of features were cut from Longhorn. Blackcomb was renamed Vienna in early 2006, as such, adoption of Vista in comparison to XP remained somewhat low. In July 2007, six months following the release of Vista, it was reported that the next version of Windows would then be codenamed Windows 7. Bill Gates, in an interview with Newsweek, suggested that Windows 7 would be more user-centric, Gates later said that Windows 7 would also focus on performance improvements. Senior Vice President Bill Veghte stated that Windows Vista users migrating to Windows 7 would not find the kind of device compatibility issues they encountered migrating from Windows XP, an estimated 1,000 developers worked on Windows 7. These were broadly divided into core operating system and Windows client experience, in October 2008, it was announced that Windows 7 would also be the official name of the operating system. The first external release to select Microsoft partners came in January 2008 with Milestone 1, at PDC2008, Microsoft demonstrated Windows 7 with its reworked taskbar. On December 27,2008, the Windows 7 Beta was leaked onto the Internet via BitTorrent. According to a performance test by ZDNet, Windows 7 Beta beat both Windows XP and Vista in several key areas, including boot and shutdown time and working with files, such as loading documents
18.
Abort, Retry, Fail?
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Abort, Retry, Fail. is a computer error message found in the DOS operating systems, which prompts the end-user for a course of action to follow. The message has been used as an example of poor usability design in computer user interfaces, a primary design consideration for the DOS family of operating systems was that software written for CP/M be portable to DOS without changes. In most CP/M systems, attempting to read a disk drive with the door open hung, waiting for a signal from the disk until the disk drive door was closed. On some hardware, it would hang until a physical disk was in the drive. Many users of CP/M were accustomed to this as a method of managing multiple disks, by opening the drive to stop the reading operation. Still, it was desirable to improve the experience if possible, in particular, for this reason, the prompt was invented in DOS. A missing disk was defined by DOS as a critical error, the default critical error handler was part of COMMAND. COM. Prompt and waited for user input, other problems were also defined as a critical error, thus causing the prompt to appear for reasons other than a missing disk or opened disk drives. Users responded to these prompts by pressing a key corresponding to action they would rather take. Available options included, Abort, Terminates the operation or program, in hindsight, this was not a good idea as the program would not do any cleanup. Abort was necessary, because early DOS did not implement Fail and it may have remained necessary for poorly written software for which Fail would have caused a loop that would have repeatedly invoked the critical error handler with no other way to exit. Retry made sense if the user could rectify the problem, for example, if the user simply forgot to close the drive latch, they could close it, retry, and the system would continue where it left off. On early hardware, retrying a disk read error would sometimes be successful, but as disk drives improved, Ignore, Return success status to the calling program or routine, despite the failure of the operation. For instance, a read error could be ignored and DOS would return whatever data was in the read buffer. Ignore did not appear in cases where it was impossible for the data to be used, for instance, Fail, Starting with MS-DOS/PC DOS3.3, the ability to return Fail from the critical error handler was added. Fail returned an error code to the program, similar to errors such as file not found. The program could then gracefully recover from the problem and this removed the biggest problem with the prompt in that there was now a useful value to return that did not crash the program or repeat the prompt. DOS3.3 COMMAND. COM provided the startup option /F in order to force the default critical error handler to return Fail on all errors
19.
MS-DOS
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MS-DOS is a discontinued operating system for x86-based personal computers mostly developed by Microsoft. MS-DOS resulted from a request in 1981 by IBM for a system to use in its IBM PC range of personal computers. Microsoft quickly bought the rights to 86-DOS from Seattle Computer Products, IBM licensed and released it in August 1981 as PC DOS1.0 for use in their PCs. During its life, several competing products were released for the x86 platform and it was also the underlying basic operating system on which early versions of Windows ran as a GUI. It is a operating system, and consumes negligible installation space. MS-DOS was a form of 86-DOS – owned by Seattle Computer Products. This first version was shipped in August 1980, Microsoft, which needed an operating system for the IBM Personal Computer hired Tim Paterson in May 1981 and bought 86-DOS1.10 for $75,000 in July of the same year. Microsoft kept the number, but renamed it MS-DOS. They also licensed MS-DOS1. 10/1.14 to IBM, within a year Microsoft licensed MS-DOS to over 70 other companies. It was designed to be an OS that could run on any 8086-family computer, thus, there were many different versions of MS-DOS for different hardware, and there is a major distinction between an IBM-compatible machine and an MS-DOS machine. This design would have worked well for compatibility, if application programs had only used MS-DOS services to perform device I/O, Microsoft omitted multi-user support from MS-DOS because Microsofts Unix-based operating system, Xenix, was fully multi-user. After the breakup of the Bell System, however, AT&T Computer Systems started selling UNIX System V, believing that it could not compete with AT&T in the Unix market, Microsoft abandoned Xenix, and in 1987 transferred ownership of Xenix to the Santa Cruz Operation. On 25 March 2014, Microsoft made the code to SCP MS-DOS1.25, as an April Fools joke in 2015, Microsoft Mobile launched a Windows Phone application called MS-DOS Mobile which was presented as a new mobile operating system and worked similar to MS-DOS. Version 3.1 – Support for Microsoft Networks Version 3.2 – First version to support 3.5 inch,720 kB floppy drives and diskettes. Version 3.21 Version 3.22 – Version 3.25 Version 3.3 – First version to support 3.5 inch,1.44 MB floppy drives and diskettes, Version 3. 3a Version 3.31 – supports FAT16B and larger drives. MS-DOS4.0 and MS-DOS4.1 – A separate branch of development with additional multitasking features and it is unrelated to any later versions, including versions 4.00 and 4.01 listed below MS-DOS4. x – includes a graphical/mouse interface. It had many bugs and compatibility issues. Version 4.00 – First version to support a hard disk partition that is greater than 32 MiB. Version 4.01 – Microsoft rewritten Version 4.00 released under MS-DOS label, First version to introduce volume serial number when formatting hard disks and floppy disks
20.
Bad command or file name
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Bad command or file name is a common error message in MS-DOS and some other operating systems. It is occasionally used as an example of a message that is perfectly accurate yet confusing to the average user. COMMAND. COM produced the message Bad command or file name when the first word of a command could not be interpreted. Though the source of the error was often a mistyped command, most modern shells produce an error message similar to foo, command not found
21.
Blue Screen of Death
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BSoDs have been present in Windows NT3.1 and all Windows operating systems released afterwards. In the Windows 9x era, incompatible DLLs or bugs in the system kernel could also cause BSoDs. Because of the instability and lack of protection in Windows 9x. The article was about the creation of the first rudimentary task manager in Windows 3. x, engadget later updated its article to correct the mistake. Until Windows Server 2012, BSoDs showed silver text on a blue background with information about current memory values. Windows Server 2012, Windows 8 and Windows 10 use a background instead. Windows 95,98 and ME BSoDs use 80×25 text mode, BSoDs in the Windows NT family use 80×50 text mode on a 720×400 screen. Windows XP BSoDs use the Lucida Console font while the Windows Vista and 7 BSoD uses the Consolas font, Windows 8, Windows Server 2012 use Segoe UI and attempt to render the BSoD at native resolution, otherwise defaulting to 640x480. Windows 10 uses the format as Windows 8 and up. In Windows NT family of operating systems, the screen of death occurs when the kernel or a driver running in kernel mode encounters an error from which it cannot recover. This is usually caused by an illegal operation being performed, the only safe action the operating system can take in this situation is to restart the computer. As a result, data may be lost, as users are not given an opportunity to save data that has not yet been saved to the hard drive. Depending on the code, it may display the address where the problem occurred. Under Windows NT, the second and third sections of the screen may contain information on all loaded drivers and a stack dump, respectively. The driver information is in three columns, the first lists the address of the driver, the second lists the drivers creation date. By default, Windows will create a dump file when a stop error occurs. Depending on the OS version, there may be several formats this can be saved in, the resulting memory dump file may be debugged later, using a kernel debugger. For Windows WinDBG or KD debuggers from Debugging Tools for Windows are used, by default, Windows XP is configured to save only a 64kB minidump when it encounters a stop error, and to then automatically reboot the computer
22.
Kernel panic
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A kernel panic, is an action taken by an operating system upon detecting an internal fatal error from which it cannot safely recover. The term is specific to Unix and Unix-like systems, for Microsoft Windows operating systems the equivalent term is Stop error. The information provided is of a technical nature and aims to assist a system administrator or software developer in diagnosing the problem. Kernel panics can also be caused by errors originating outside of kernel space, for example, many Unix OSes panic if the init process, which runs in userspace, terminates. The Unix kernel maintains internal consistency and runtime correctness with assertions as the detection mechanism. The basic assumption is that the hardware and the software should perform correctly, the kernel panic was introduced in an early version of Unix and demonstrated a major difference between the design philosophies of Unix and its predecessor Multics. He said, We left all that stuff out, if theres an error, we have this routine called panic, and when it is called, the machine crashes, and you holler down the hall, Hey, reboot it. Source code of panic function in V6 UNIX, As the Unix codebase was enhanced, a panic may occur as a result of a hardware failure or a software bug in the operating system. In many cases, the system is capable of continued operation after an error has occurred. After recompiling a kernel binary image from source code, a kernel panic while booting the resulting kernel is a problem if the kernel was not correctly configured, compiled or installed. Add-on hardware or malfunctioning RAM could also be sources of fatal kernel errors during start up, a kernel may also go into panic if it is unable to locate a root file system. During the final stages of kernel userspace initialization, a panic is typically triggered if the spawning of init fails, in this case, the kernel normally continues to run after killing the offending process. As an oops could cause some subsystems or resources to become unavailable, in Linux kernel, a kernel panic causes keyboard LEDs to blink as a visual indication of a critical condition. When a kernel panic occurs in Mac OS X10.2 through 10.7, prior to 10.2, a more traditional Unix-style panic message was displayed, in 10.8 and later, the computer automatically reboots and displays a message after the restart. The format of the message varies from version to version,10. 0–10.1, The system displays text on the screen, giving details about the error, and becomes unresponsive. 10.2, Rolls down a black transparent curtain then displays a message on a white background informing the user that they should restart the computer, the message is shown in English, French, German and Japanese. 10. 3–10.5, The kernel panic is almost the same as version 10.2,10. 6–10.7, The text has been revised and now includes a Spanish translation. 10.8 and later, The computer becomes unresponsive before it immediately reboots, when the computer starts back up, it shows a message for a few seconds about the computer restarting because of a kernel panic, and then the computer restarts back up
23.
Linux
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Linux is a Unix-like computer operating system assembled under the model of free and open-source software development and distribution. The defining component of Linux is the Linux kernel, an operating system kernel first released on September 17,1991 by Linus Torvalds, the Free Software Foundation uses the name GNU/Linux to describe the operating system, which has led to some controversy. Linux was originally developed for computers based on the Intel x86 architecture. Because of the dominance of Android on smartphones, Linux has the largest installed base of all operating systems. Linux is also the operating system on servers and other big iron systems such as mainframe computers. It is used by around 2. 3% of desktop computers, the Chromebook, which runs on Chrome OS, dominates the US K–12 education market and represents nearly 20% of the sub-$300 notebook sales in the US. Linux also runs on embedded systems – devices whose operating system is built into the firmware and is highly tailored to the system. This includes TiVo and similar DVR devices, network routers, facility automation controls, televisions, many smartphones and tablet computers run Android and other Linux derivatives. The development of Linux is one of the most prominent examples of free, the underlying source code may be used, modified and distributed—commercially or non-commercially—by anyone under the terms of its respective licenses, such as the GNU General Public License. Typically, Linux is packaged in a known as a Linux distribution for both desktop and server use. Distributions intended to run on servers may omit all graphical environments from the standard install, because Linux is freely redistributable, anyone may create a distribution for any intended use. The Unix operating system was conceived and implemented in 1969 at AT&Ts Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, first released in 1971, Unix was written entirely in assembly language, as was common practice at the time. Later, in a key pioneering approach in 1973, it was rewritten in the C programming language by Dennis Ritchie, the availability of a high-level language implementation of Unix made its porting to different computer platforms easier. Due to an earlier antitrust case forbidding it from entering the computer business, as a result, Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs, freed of the legal obligation requiring free licensing, the GNU Project, started in 1983 by Richard Stallman, has the goal of creating a complete Unix-compatible software system composed entirely of free software. Later, in 1985, Stallman started the Free Software Foundation, by the early 1990s, many of the programs required in an operating system were completed, although low-level elements such as device drivers, daemons, and the kernel were stalled and incomplete. Linus Torvalds has stated that if the GNU kernel had been available at the time, although not released until 1992 due to legal complications, development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Torvalds has also stated that if 386BSD had been available at the time, although the complete source code of MINIX was freely available, the licensing terms prevented it from being free software until the licensing changed in April 2000
24.
Unix
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Among these is Apples macOS, which is the Unix version with the largest installed base as of 2014. Many Unix-like operating systems have arisen over the years, of which Linux is the most popular, Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmer users. The system grew larger as the system started spreading in academic circles, as users added their own tools to the system. Unix was designed to be portable, multi-tasking and multi-user in a time-sharing configuration and these concepts are collectively known as the Unix philosophy. By the early 1980s users began seeing Unix as a universal operating system. Under Unix, the system consists of many utilities along with the master control program. To mediate such access, the kernel has special rights, reflected in the division between user space and kernel space, the microkernel concept was introduced in an effort to reverse the trend towards larger kernels and return to a system in which most tasks were completed by smaller utilities. In an era when a standard computer consisted of a disk for storage and a data terminal for input and output. However, modern systems include networking and other new devices, as graphical user interfaces developed, the file model proved inadequate to the task of handling asynchronous events such as those generated by a mouse. In the 1980s, non-blocking I/O and the set of inter-process communication mechanisms were augmented with Unix domain sockets, shared memory, message queues, and semaphores. In microkernel implementations, functions such as network protocols could be moved out of the kernel, Multics introduced many innovations, but had many problems. Frustrated by the size and complexity of Multics but not by the aims and their last researchers to leave Multics, Ken Thompson, Dennis Ritchie, M. D. McIlroy, and J. F. Ossanna, decided to redo the work on a much smaller scale. The name Unics, a pun on Multics, was suggested for the project in 1970. Peter H. Salus credits Peter Neumann with the pun, while Brian Kernighan claims the coining for himself, in 1972, Unix was rewritten in the C programming language. Bell Labs produced several versions of Unix that are referred to as Research Unix. In 1975, the first source license for UNIX was sold to faculty at the University of Illinois Department of Computer Science, UIUC graduate student Greg Chesson was instrumental in negotiating the terms of this license. During the late 1970s and early 1980s, the influence of Unix in academic circles led to adoption of Unix by commercial startups, including Sequent, HP-UX, Solaris, AIX. In the late 1980s, AT&T Unix System Laboratories and Sun Microsystems developed System V Release 4, in the 1990s, Unix-like systems grew in popularity as Linux and BSD distributions were developed through collaboration by a worldwide network of programmers
25.
MacOS
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Within the market of desktop, laptop and home computers, and by web usage, it is the second most widely used desktop OS after Microsoft Windows. Launched in 2001 as Mac OS X, the series is the latest in the family of Macintosh operating systems, Mac OS X succeeded classic Mac OS, which was introduced in 1984, and the final release of which was Mac OS9 in 1999. An initial, early version of the system, Mac OS X Server 1.0, was released in 1999, the first desktop version, Mac OS X10.0, followed in March 2001. In 2012, Apple rebranded Mac OS X to OS X. Releases were code named after big cats from the release up until OS X10.8 Mountain Lion. Beginning in 2013 with OS X10.9 Mavericks, releases have been named after landmarks in California, in 2016, Apple rebranded OS X to macOS, adopting the nomenclature that it uses for their other operating systems, iOS, watchOS, and tvOS. The latest version of macOS is macOS10.12 Sierra, macOS is based on technologies developed at NeXT between 1985 and 1997, when Apple acquired the company. The X in Mac OS X and OS X is pronounced ten, macOS shares its Unix-based core, named Darwin, and many of its frameworks with iOS, tvOS and watchOS. A heavily modified version of Mac OS X10.4 Tiger was used for the first-generation Apple TV, Apple also used to have a separate line of releases of Mac OS X designed for servers. Beginning with Mac OS X10.7 Lion, the functions were made available as a separate package on the Mac App Store. Releases of Mac OS X from 1999 to 2005 can run only on the PowerPC-based Macs from the time period, Mac OS X10.5 Leopard was released as a Universal binary, meaning the installer disc supported both Intel and PowerPC processors. In 2009, Apple released Mac OS X10.6 Snow Leopard, in 2011, Apple released Mac OS X10.7 Lion, which no longer supported 32-bit Intel processors and also did not include Rosetta. All versions of the system released since then run exclusively on 64-bit Intel CPUs, the heritage of what would become macOS had originated at NeXT, a company founded by Steve Jobs following his departure from Apple in 1985. There, the Unix-like NeXTSTEP operating system was developed, and then launched in 1989 and its graphical user interface was built on top of an object-oriented GUI toolkit using the Objective-C programming language. This led Apple to purchase NeXT in 1996, allowing NeXTSTEP, then called OPENSTEP, previous Macintosh operating systems were named using Arabic numerals, e. g. Mac OS8 and Mac OS9. The letter X in Mac OS Xs name refers to the number 10 and it is therefore correctly pronounced ten /ˈtɛn/ in this context. However, a common mispronunciation is X /ˈɛks/, consumer releases of Mac OS X included more backward compatibility. Mac OS applications could be rewritten to run natively via the Carbon API, the consumer version of Mac OS X was launched in 2001 with Mac OS X10.0. Reviews were variable, with praise for its sophisticated, glossy Aqua interface
26.
File system fragmentation
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It is a special case of data fragmentation. File system fragmentation increases disk head movement or seek time, which are known to hinder throughput, in addition, file systems cannot sustain unlimited fragmentation. The correction to existing fragmentation is to reorganize files and free space back into contiguous areas, when a file system is first initialized on a partition, it contains only a few small internal structures and is otherwise one contiguous block of empty space. This means that the system is able to place newly created files anywhere on the partition. For some time after creation, files can be laid out near-optimally, when the operating system and applications are installed or archives are unpacked, separate files end up occurring sequentially so related files are positioned close to each other. As existing files are deleted or truncated, new regions of space are created. As time goes on, and the factors are continuously present. Shorter regions of free space also mean that the system is no longer able to allocate new files contiguously. This is especially true when the system becomes full and large contiguous regions of free space are unavailable. The following example is a simplification of a complicated subject. Consider the following scenario, A new disk has had five files, named A, B, C, D and E, each file is using 10 blocks of space. The remainder of the space is one free block. Thus, additional files can be created and saved after the file E, if the file B is deleted, a second region of ten blocks of free space is created, and the disk becomes fragmented. The empty space is left there, marked as and available for later use. The file system could defragment the disk immediately after a deletion, if another new file called G, which needs only three blocks, is added, it could then occupy the space after F and before C. The third option is impossible when there is no single contiguous free space large enough to hold the new file, thus the usual practice is simply to create an extent somewhere else and chain the new extent onto the old one. Material added to the end of file F would be part of the same extent, but if there is so much material that no room is available after the last extent, then another extent would have to be created, and so on. Eventually the file system has free segments in many places and some files may be spread over many extents, access time for those files may become excessively long
27.
Acorn Computers
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Acorn Computers Ltd. was a British computer company established in Cambridge, England, in 1978. The company produced a number of computers which were popular in the UK, including the Acorn Electron. Acorns BBC Micro computer dominated the UK educational computer market during the 1980s and it is more known for its BBC Micro model B computer than for its other products. Though the company was broken up several independent operations in 1998. One of its systems, RISC OS, continues to be developed by RISC OS Open. Some of Acorns former subsidiaries lived on, ARM Holdings technology is dominant in the mobile phone, Acorn is sometimes referred to as the British Apple and has been compared to Fairchild Semiconductor for being a catalyst for start-ups. In 2010, the company was listed by David Meyer in ZDNet as number nine in a feature of top ten fallen Dead IT giants, many British IT professionals gained their early experiences on Acorns, which were often more technically advanced than commercially successful US hardware. On 25 July 1961, Clive Sinclair founded Sinclair Radionics to develop, the failure of the Black Watch wristwatch and the calculator markets move from LEDs to LCDs led to financial problems, and Sinclair approached government body the National Enterprise Board for help. After losing control of the company to the NEB, Sinclair encouraged Chris Curry to leave Radionics and get Science of Cambridge up and running. In June 1978, SoC launched a kit, the Mk 14, that Curry wanted to develop further. During the development of the Mk 14, Hermann Hauser, a friend of Currys, had been visiting SoCs offices and had interested in the product. Curry and Hauser decided to pursue their joint interest in microcomputers and, on 5 December 1978, CPU soon obtained a consultancy contract to develop a microprocessor-based controller for a fruit machine for Ace Coin Equipment of Wales. The ACE project was started at office space obtained at 4a Market Hill in Cambridge, initially, the ACE controller was based on a National Semiconductor SC/MP microprocessor, but soon the switch to a MOS Technology 6502 was made. CPU had financed the development of a SC/MP based microcomputer system using the income from its design-and-build consultancy. This system was launched in January 1979 as the first product of Acorn Computer Ltd. a trading name used by CPU to keep the risks of the two different lines of business separate, the microcomputer kit was named as Acorn System 75. Acorn was chosen because the system was to be expandable. It also had the attraction of appearing before Apple Computer in a telephone directory, around this time, CPU and Andy Hopper set up Orbis Ltd. CPU purchased Orbis, and Hoppers Orbis shares were exchanged for shares in CPU Ltd, CPUs role gradually changed as its Acorn brand grew, and soon CPU was simply the holding company and Acorn was responsible for development work
28.
Guru Meditation
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The Guru Meditation is an error notice displayed by early versions of the Commodore Amiga computer when they crashed. It is analogous to the Blue Screen of Death in Microsoft Windows operating systems and it has later been used as a message for unrecoverable errors in software such as Varnish and VirtualBox. When a Guru Meditation is displayed, the options are to reboot by pressing the mouse button. The alert itself appears as a rectangular box located in the upper portion of the screen. Its border and text are red for a normal Guru Meditation, or green/yellow for a Recoverable Alert, the screen goes black, and the power and disk-activity LEDs may blink immediately before the alert appears. In AmigaOS1. x, programmed in ROMs known as Kickstart 1.1,1.2 and 1.3, the errors are always red. In AmigaOS2. x and 3. x, recoverable alerts are yellow, the alert occurred when there was a fatal problem with the system. If the system had no means of recovery, it could display the alert, in extreme cases, the alert could even be displayed if the systems memory was completely exhausted. The error is displayed as two fields, separated by a period, the format is #0000000x. yyyyyyyy in case of a CPU error, or #aabbcccc. dddddddd in case of a system software error. The first field is either the Motorola 68000 exception number that occurred or an internal error identifier, the second can be the address of a Task structure, or the address of a memory block whose allocation or deallocation failed. It is never the address of the code that caused the error, if the cause of the crash is uncertain, this number is rendered as 48454C50, which stands for HELP in hexadecimal ASCII characters. The text of the messages was completely baffling to most users. Only highly technically adept Amiga users would know, for example, that exception 3 was an address error, users without this specialized knowledge would have no recourse but to look for a Guru or to simply reboot the machine and hope for the best. There was a commercially available error handler for AmigaOS, before version 2.04 and it was able to deal with many kinds of errors and gave the user a choice to either remove the offending process and associated screen, or allow the machine to show the Guru Meditation. In many cases, removal of the process gave one the choice to save ones data. When the damage was not extensive, one was able to continue using the machine, however, it did not save the user from all errors, as one may have still seen this error occasionally. Recoverable Alerts are non-critical crashes in the computer system, in most cases, it is possible to resume work and save files after a Recoverable Alert, while a normal, red Guru Meditation always results in an immediate reboot. It is, however, still recommended to reboot as soon as possible after encountering a Recoverable Alert because the system may be in a state that can cause data corruption
29.
Commodore Amiga
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The Amiga is a family of personal computers sold by Commodore in the 1980s and 1990s. The Amiga provided a significant upgrade from earlier 8-bit home computers, the Amiga 1000 was officially released in July 1985, but a series of production problems meant it did not become widely available until early 1986. The best selling model, the Amiga 500, was introduced in 1987 and became one of the home computers of the late 1980s. The A3000, introduced in 1990, started the second generation of Amiga systems, followed by the A500+, finally, as the third generation, the A1200 and the A4000 were released in late 1992. The platform became particularly popular for gaming and programming demos and it also found a prominent role in the desktop video, video production, and show control business, leading to video editing systems such as the Video Toaster. The Amigas native ability to play back multiple digital sound samples made it a popular platform for early tracker music software. It was also an expensive alternative to the Apple Macintosh. Initially, the Amiga was developed alongside various Commodore PC clones, Commodore ultimately went bankrupt in April 1994 after the Amiga CD32 model failed in the marketplace. Since the demise of Commodore, various groups have marketed successors to the original Amiga line, including Genesi, Eyetech, ACube Systems Srl, likewise, AmigaOS has influenced replacements, clones and compatible systems such as MorphOS, AmigaOS4 and AROS. The Amiga was so far ahead of its time that almost nobody—including Commodores marketing department—could fully articulate what it was all about. Today, its obvious the Amiga was the first multimedia computer, but in those days it was derided as a machine because few people grasped the importance of advanced graphics, sound. Nine years later, vendors are still struggling to make systems that work like 1985 Amigas, Jay Miner joined Atari in the 1970s to develop custom integrated circuits, and led development of the Atari 2600s TIA. Almost as soon as its development was complete, the team developing a much more sophisticated set of chips, CTIA, ANTIC and POKEY. With the 8-bit lines launch in 1979, Miner again started looking at a next generation chipset, Miner wanted to start work with the new Motorola 68000, but management was only interested in another MOS6502 based system. Miner left the company, and the industry, shortly thereafter, in 1982, Larry Kaplan was approached by a number of investors who wanted to develop a new game platform. Kaplan hired Miner to run the side of the newly formed company. The system was code-named Lorraine in keeping with Miners policy of giving systems female names, in case the company presidents wife. When Kaplan left the late in 1982 to rejoin Atari, Miner was promoted to head engineer
30.
VirtualBox
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Oracle VM VirtualBox is a free and open-source hypervisor for x86 computers currently being developed by Oracle Corporation. Developed initially by Innotek GmbH, it was acquired by Sun Microsystems in 2008 which was in turn acquired by Oracle in 2010, VirtualBox may be installed on a number of host operating systems, including, Linux, macOS, Windows, Solaris, and OpenSolaris. There are also ports to FreeBSD and Genode, for some guest operating systems, a Guest Additions package of device drivers and system applications is available which typically improves performance, especially of graphics. Innotek GmbH also contributed to the development of OS/2 and Linux support in virtualization, Sun Microsystems acquired Innotek in February 2008. Oracle Corporation acquired Sun in January 2010 and re-branded the product as Oracle VM VirtualBox, the core package is, since version 4 in December 2010, free software under GNU General Public License version 2. The separate VirtualBox Oracle VM VirtualBox extension pack providing support for USB2, Oracle defines personal use as any situation in which one person installs the software, and only that individual, and their friends and family, use the software. Oracle does not care if that use is for commercial or non-commercial purposes, prior to version 4, there were two different packages of the VirtualBox software. The full package was offered free under the PUEL, with licenses for commercial deployment purchasable from Oracle. A second package called the VirtualBox Open Source Edition was released under GPLv2 and this removed the same proprietary components not available under GPLv2. Building the BIOS for VirtualBox since version 4, users of VirtualBox can load multiple guest OSs under a single host operating-system. Each guest can be started, paused and stopped independently within its own virtual machine, the user can independently configure each VM and run it under a choice of software-based virtualization or hardware assisted virtualization if the underlying host hardware supports this. The host OS and guest OSs and applications can communicate with other through a number of mechanisms including a common clipboard. Guest VMs can also communicate with each other if configured to do so. In the absence of hardware-assisted virtualization, VirtualBox adopts a standard software-based virtualization approach and this mode supports 32-bit guest OSs which run in rings 0 and 3 of the Intel ring architecture. The system reconfigures the guest OS code, which would run in ring 0. This replaces the instruction with a jump to a VM-safe equivalent compiled code fragment in hypervisor memory, the guest user-mode code, running in ring 3, generally runs directly on the host hardware in ring 3. In both cases, VirtualBox uses CSAM and PATM to inspect and patch the offending instructions whenever a fault occurs, VirtualBox also contains a dynamic recompiler, based on QEMU to recompile any real mode or protected mode code entirely. Using these techniques, VirtualBox can achieve a performance comparable to that of VMware, VirtualBox supports both Intels VT-x and AMDs AMD-V hardware-virtualization
31.
HTTP 404
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In the code 404, the first digit indicates a client error, such as a mistyped Uniform Resource Locator. The following two digits indicate the specific error encountered, hTTPs use of three-digit codes is similar to the use of such codes in earlier protocols such as FTP and NNTP. At the HTTP level, a 404 response code is followed by a human-readable reason phrase, the HTTP specification suggests the phrase Not Found and many web servers by default issue an HTML page that includes both the 404 code and the Not Found phrase. A404 error is often returned when pages have been moved or deleted, because these two options require special server configuration, most websites do not make use of them. 404 errors should not be confused with DNS errors, which appear when the given URL refers to a name that does not exist. A404 error indicates that the server itself was found, the protocol level phrase, which is hidden from the user, is rarely customized. Internet Explorer, however, will not display custom pages unless they are larger than 512 bytes, Google Chrome includes similar functionality, where the 404 is replaced with alternative suggestions generated by Google algorithms, if the page is under 512 bytes in size. Another problem is that if the page does not provide a favicon, Many organizations use 404 error pages as an opportunity to inject humor into what may otherwise be a serious website. For example, Metro UK shows a bear on a skateboard. While many websites send additional information in a 404 error message—such as a link to the homepage of a website or a search box—some also endeavor to find the correct web page the user wanted, extensions are available for some popular content management systems to do this. A number of tools exist that crawl through a website to find pages that return 404 status codes and these tools can be helpful in finding links that exist within a particular website. The limitation of these tools is that they only find links within one particular website, as a result, these tools miss out on 83% of the 404s on websites. One way around this is to find 404 errors by analyzing external links, another common method is tracking traffic to 404 pages using log file analysis. This can be useful to understand more about what 404s users reached on the site, another method of tracking traffic to 404 pages is using JavaScript-based traffic tracking tools. Some websites report a not found error by returning a web page with a 200 OK response code, falsely reporting that the page loaded properly. Soft 404s are problematic for automated methods of discovering whether a link is broken, some search engines, like Yahoo, use automated processes to detect soft 404s. This can also be done on purpose to some browsers to display a customized 404 error message rather than replacing what is served with a browser-specific friendly error message. This can confuse programs that expect and act on specific responses, other ISPs return a HTTP403 forbidden error in the same circumstances
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World Wide Web
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The World Wide Web is an information space where documents and other web resources are identified by Uniform Resource Locators, interlinked by hypertext links, and can be accessed via the Internet. English scientist Tim Berners-Lee invented the World Wide Web in 1989 and he wrote the first web browser computer program in 1990 while employed at CERN in Switzerland. The Web browser was released outside of CERN in 1991, first to research institutions starting in January 1991. The World Wide Web has been central to the development of the Information Age and is the primary tool billions of people use to interact on the Internet, Web pages are primarily text documents formatted and annotated with Hypertext Markup Language. In addition to formatted text, web pages may contain images, video, audio, embedded hyperlinks permit users to navigate between web pages. Multiple web pages with a theme, a common domain name. Website content can largely be provided by the publisher, or interactive where users contribute content or the content depends upon the user or their actions, websites may be mostly informative, primarily for entertainment, or largely for commercial, governmental, or non-governmental organisational purposes. In the 2006 Great British Design Quest organised by the BBC and the Design Museum, Tim Berners-Lees vision of a global hyperlinked information system became a possibility by the second half of the 1980s. By 1985, the global Internet began to proliferate in Europe, in 1988 the first direct IP connection between Europe and North America was made and Berners-Lee began to openly discuss the possibility of a web-like system at CERN. Such a system, he explained, could be referred to using one of the meanings of the word hypertext. At this point HTML and HTTP had already been in development for two months and the first Web server was about a month from completing its first successful test. While the read-only goal was met, accessible authorship of web content took longer to mature, with the concept, WebDAV, blogs, Web 2.0. The proposal was modelled after the SGML reader Dynatext by Electronic Book Technology, a NeXT Computer was used by Berners-Lee as the worlds first web server and also to write the first web browser, WorldWideWeb, in 1990. By Christmas 1990, Berners-Lee had built all the necessary for a working Web, the first web browser. The first web site, which described the project itself, was published on 20 December 1990, jones stored it on a magneto-optical drive and on his NeXT computer. On 6 August 1991, Berners-Lee published a summary of the World Wide Web project on the newsgroup alt. hypertext. This date is confused with the public availability of the first web servers. The first server outside Europe was installed at the Stanford Linear Accelerator Center in Palo Alto, California, accounts differ substantially as to the date of this event
33.
Not a typewriter
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In computing, Not a typewriter or ENOTTY is an error code defined in the errno. h found on many Unix systems. This code is now used to indicate that an invalid ioctl number was specified in a system call. This error originated in early UNIX, in Version 6 UNIX and earlier, I/O control was limited to serial-connected terminal devices, typically a teletype, through the gtty and stty system calls. If an attempt was made to use these calls on a non-terminal device, when the stty/gtty system calls were replaced with the more general ioctl call, the ENOTTY error code was retained. Typewriter was what early Unix systems called a terminal and this usage goes all the way back to the First Edition of the Unix Programmers Manual, dated November 3,1971. For example, the description of the hup command was hup hangs up the phone on the typewriter which uses it, the abbreviation TTY, which occurs widely even in modern UNIX systems, stood for Teletype. The generic term typewriter was used because Teletype was a registered trademark of AT&T subsidiary Teletype Corporation and was too specific. The name Teletype was derived from the general term, teletypewriter. Because ioctl is now supported on other devices than terminals, some display a different message such as Inappropriate ioctl for device instead. In some cases, this message will occur even when no ioctl has been issued by the program and this is due to the way the isatty library routine works. The error code errno is only set when a system call fails, one of the first system calls made by the C standard I/O library is in an isatty call used to determine if the program is being run interactively by a human or as part of a pipeline. For many years the UNIX mail program sendmail contained this bug, when mail was delivered from another system, the mail program was being run non-interactively
34.
PC LOAD LETTER
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PC LOAD LETTER is a printer error message that has entered popular culture as a technology meme referring to a confusing or inappropriate error message. The PC LOAD LETTER message is encountered when printing on older HP LaserJet printers such as the LaserJet II, III, and 4 series. It means that the printer is trying to print a document whose paper size is set to letter when no letter size paper is available, the error message comprises three parts. PC is an abbreviation for paper cassette, the tray which holds blank paper for the printer to use and these two-character codes are a legacy feature carried over from the first LaserJet printers, which could only use a two-character display for all printer status and error messages. Load, in context, is an instruction to refill the paper tray. Letter is the paper size used in the United States. Thus, the error is instructing the user to refill the paper tray with letter-sized paper, a variant is PC LOAD LEGAL, meaning that the printer needs more legal size paper. The message confuses people for several reasons, the word LOAD is also ambiguous, as it can also refer to the transfer of electronic data between disk and memory. Furthermore, the word LETTER is associated with paper size only in the US, Canada and some Latin American countries, older LaserJet printers do not automatically resize a page when the page size of a document does not match the paper that is loaded in the printer. When trying to print a document whose paper size is set to letter on A4-sized paper the message occurs, the error PC LOAD A4 appears in countries using this paper size. However, as many programs use letter as the default format, the LaserJet 5 introduced an easy-to-find GO button to override the warning message. The error messages vagueness was mocked in the 1999 comedy film Office Space, bad command or file name lp0 on fire
35.
Syntax error
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In computer science, a syntax error is an error in the syntax of a sequence of characters or tokens that is intended to be written in a particular programming language. For compiled languages, syntax errors are detected at compile-time, a program will not compile until all syntax errors are corrected. For interpreted languages, however, an error may be detected during program execution. There is some disagreement as to just what errors are syntax errors, for example, some would say that the use of an uninitialized variables value in Java code is a syntax error, but many others would disagree and would classify this as a semantic error. A syntax error may occur when an invalid equation is entered into a calculator. This can be caused, for instance, by opening brackets without closing them, or less commonly, however, a variable in Java cannot have a space in between, so the syntactically correct line would be System. out. println. A compiler will flag a syntax error when given source code that does not meet the requirements of the language grammar, type errors and undeclared variable errors are sometimes considered to be syntax errors when they are detected at compile-time. However, it is common to such errors as semantic errors instead
36.
HTTP 504
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This is a list of Hypertext Transfer Protocol response status codes. It includes codes from IETF Request for Comments, other specifications, the first digit of the status code specifies one of five standard classes of responses. The message phrases shown are typical, but any human-readable alternative may be provided, unless otherwise stated, the status code is part of the HTTP/1.1 standard. The Internet Assigned Numbers Authority maintains the registry of HTTP status codes. An informational response indicates that the request was received and understood and it is issued on a provisional basis while request processing continues. It alerts the client to wait for a final response, the message consists only of the status line and optional header fields, and is terminated by an empty line. As the HTTP/1.0 standard did not define any 1xx status codes,100 Continue The server has received the request headers and the client should proceed to send the request body. Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a check the requests headers, a client must send Expect, 100-continue as a header in its initial request. The response 417 Expectation Failed indicates the request should not be continued,101 Switching Protocols The requester has asked the server to switch protocols and the server has agreed to do so. 102 Processing A WebDAV request may contain many sub-requests involving file operations and this code indicates that the server has received and is processing the request, but no response is available yet. This prevents the client from timing out and assuming the request was lost and this class of status codes indicates the action requested by the client was received, understood, accepted, and processed successfully. 200 OK Standard response for successful HTTP requests, the actual response will depend on the request method used. In a GET request, the response will contain an entity corresponding to the requested resource, in a POST request, the response will contain an entity describing or containing the result of the action. 201 Created The request has been fulfilled, resulting in the creation of a new resource,202 Accepted The request has been accepted for processing, but the processing has not been completed. The request might or might not be acted upon. 203 Non-Authoritative Information The server is a proxy that received a 200 OK from its origin. 204 No Content The server successfully processed the request and is not returning any content,205 Reset Content The server successfully processed the request, but is not returning any content
37.
Computer program
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A computer program is a collection of instructions that performs a specific task when executed by a computer. A computer requires programs to function, and typically executes the programs instructions in a processing unit. A computer program is written by a computer programmer in a programming language. From the program in its form of source code, a compiler can derive machine code—a form consisting of instructions that the computer can directly execute. Alternatively, a program may be executed with the aid of an interpreter. A part of a program that performs a well-defined task is known as an algorithm. A collection of programs, libraries and related data are referred to as software. Computer programs may be categorized along functional lines, such as software or system software. The earliest programmable machines preceded the invention of the digital computer, in 1801, Joseph-Marie Jacquard devised a loom that would weave a pattern by following a series of perforated cards. Patterns could be weaved and repeated by arranging the cards, in 1837, Charles Babbage was inspired by Jacquards loom to attempt to build the Analytical Engine. The names of the components of the device were borrowed from the textile industry. In the textile industry, yarn was brought from the store to be milled, the device would have had a store—memory to hold 1,000 numbers of 40 decimal digits each. Numbers from the store would then have then transferred to the mill. It was programmed using two sets of perforated cards—one to direct the operation and the other for the input variables, however, after more than 17,000 pounds of the British governments money, the thousands of cogged wheels and gears never fully worked together. During a nine-month period in 1842–43, Ada Lovelace translated the memoir of Italian mathematician Luigi Menabrea, the memoir covered the Analytical Engine. The translation contained Note G which completely detailed a method for calculating Bernoulli numbers using the Analytical Engine and this note is recognized by some historians as the worlds first written computer program. In 1936, Alan Turing introduced the Universal Turing machine—a theoretical device that can model every computation that can be performed on a Turing complete computing machine and it is a finite-state machine that has an infinitely long read/write tape. The machine can move the back and forth, changing its contents as it performs an algorithm
38.
Microsoft Windows
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Microsoft Windows is a metafamily of graphical operating systems developed, marketed, and sold by Microsoft. It consists of families of operating systems, each of which cater to a certain sector of the computing industry with the OS typically associated with IBM PC compatible architecture. Active Windows families include Windows NT, Windows Embedded and Windows Phone, defunct Windows families include Windows 9x, Windows 10 Mobile is an active product, unrelated to the defunct family Windows Mobile. Microsoft introduced an operating environment named Windows on November 20,1985, Microsoft Windows came to dominate the worlds personal computer market with over 90% market share, overtaking Mac OS, which had been introduced in 1984. Apple came to see Windows as an encroachment on their innovation in GUI development as implemented on products such as the Lisa. On PCs, Windows is still the most popular operating system, however, in 2014, Microsoft admitted losing the majority of the overall operating system market to Android, because of the massive growth in sales of Android smartphones. In 2014, the number of Windows devices sold was less than 25% that of Android devices sold and this comparison however may not be fully relevant, as the two operating systems traditionally target different platforms. As of September 2016, the most recent version of Windows for PCs, tablets, smartphones, the most recent versions for server computers is Windows Server 2016. A specialized version of Windows runs on the Xbox One game console, Microsoft, the developer of Windows, has registered several trademarks each of which denote a family of Windows operating systems that target a specific sector of the computing industry. It now consists of three operating system subfamilies that are released almost at the time and share the same kernel. Windows, The operating system for personal computers, tablets. The latest version is Windows 10, the main competitor of this family is macOS by Apple Inc. for personal computers and Android for mobile devices. Windows Server, The operating system for server computers, the latest version is Windows Server 2016. Unlike its clients sibling, it has adopted a strong naming scheme, the main competitor of this family is Linux. Windows PE, A lightweight version of its Windows sibling meant to operate as an operating system, used for installing Windows on bare-metal computers. The latest version is Windows PE10.0.10586.0, Windows Embedded, Initially, Microsoft developed Windows CE as a general-purpose operating system for every device that was too resource-limited to be called a full-fledged computer. The following Windows families are no longer being developed, Windows 9x, Microsoft now caters to the consumers market with Windows NT. Windows Mobile, The predecessor to Windows Phone, it was a mobile operating system
39.
Android (operating system)
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Android is a mobile operating system developed by Google, based on the Linux kernel and designed primarily for touchscreen mobile devices such as smartphones and tablets. In addition to devices, Google has further developed Android TV for televisions, Android Auto for cars. Variants of Android are also used on notebooks, game consoles, digital cameras, beginning with the first commercial Android device in September 2008, the operating system has gone through multiple major releases, with the current version being 7.0 Nougat, released in August 2016. Android applications can be downloaded from the Google Play store, which features over 2.7 million apps as of February 2017, Android has been the best-selling OS on tablets since 2013, and runs on the vast majority of smartphones. In September 2015, Android had 1.4 billion monthly active users, Android is popular with technology companies that require a ready-made, low-cost and customizable operating system for high-tech devices. The success of Android has made it a target for patent, Android Inc. was founded in Palo Alto, California in October 2003 by Andy Rubin, Rich Miner, Nick Sears, and Chris White. Rubin described the Android project as tremendous potential in developing smarter mobile devices that are aware of its owners location. The early intentions of the company were to develop an operating system for digital cameras. Despite the past accomplishments of the founders and early employees, Android Inc. operated secretly and that same year, Rubin ran out of money. Steve Perlman, a friend of Rubin, brought him $10,000 in cash in an envelope. In July 2005, Google acquired Android Inc. for at least $50 million and its key employees, including Rubin, Miner and White, joined Google as part of the acquisition. Not much was known about Android at the time, with Rubin having only stated that they were making software for mobile phones, at Google, the team led by Rubin developed a mobile device platform powered by the Linux kernel. Google marketed the platform to handset makers and carriers on the promise of providing a flexible, upgradeable system, Google had lined up a series of hardware components and software partners and signaled to carriers that it was open to various degrees of cooperation. Speculation about Googles intention to enter the communications market continued to build through December 2006. In September 2007, InformationWeek covered an Evalueserve study reporting that Google had filed several patent applications in the area of mobile telephony, the first commercially available smartphone running Android was the HTC Dream, also known as T-Mobile G1, announced on September 23,2008. Since 2008, Android has seen numerous updates which have improved the operating system, adding new features. Each major release is named in order after a dessert or sugary treat, with the first few Android versions being called Cupcake, Donut, Eclair. In 2010, Google launched its Nexus series of devices, a lineup in which Google partnered with different device manufacturers to produce new devices and introduce new Android versions
40.
System call
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In computing, a system call is the programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. This may include hardware-related services, creation and execution of new processes, system calls provide an essential interface between a process and the operating system. In most systems, system calls can only be made from userspace processes, while in some systems, OS/360 and successors for example, the architecture of most modern processors, with the exception of some embedded systems, involves a security model. The operating system executes at the highest level of privilege, and allows applications to request services via system calls, generally, systems provide a library or API that sits between normal programs and the operating system. The librarys wrapper functions expose an ordinary function calling convention for using the system call, in this way the library, which exists between the OS and the application, increases portability. The call to the function itself does not cause a switch to kernel mode and is usually a normal subroutine call. The actual system call does transfer control to the kernel, for example, in Unix-like systems, fork and execve are C library functions that in turn execute instructions that invoke the fork and exec system calls. On exokernel based systems, the library is especially important as an intermediary, on exokernels, libraries shield user applications from the very low level kernel API, and provide abstractions and resource management. IBM operating systems descended from OS/360 and DOS/360, including z/OS and z/VSE and this reflects their origin at a time when programming in assembly language was more common than high-level language usage. IBM system calls are not directly executable by high-level language programs. On Unix, Unix-like and other POSIX-compliant operating systems, popular system calls are open, read, write, close, wait, exec, fork, exit, many modern operating systems have hundreds of system calls. For example, Linux and OpenBSD each have over 300 different calls, NetBSD has close to 500, FreeBSD has over 500, Windows 7 has close to 700, while Plan 9 has 51. This special ability of the program is also implemented with a system call. Implementing system calls requires a transfer from user space to kernel space. A typical way to implement this is to use a software interrupt or trap, interrupts transfer control to the operating system kernel so software simply needs to set up some register with the system call number needed, and execute the software interrupt. This is the only provided for many RISC processors. For example, the x86 instruction set contains the instructions SYSCALL/SYSRET and these are fast control transfer instructions that are designed to quickly transfer control to the kernel for a system call without the overhead of an interrupt. Linux 2.5 began using this on the x86, where available, formerly it used the INT instruction, an older x86 mechanism is the call gate
