1.
Computing
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Computing is any goal-oriented activity requiring, benefiting from, or creating a mathematical sequence of steps known as an algorithm — e. g. through computers. The field of computing includes computer engineering, software engineering, computer science, information systems, the ACM Computing Curricula 2005 defined computing as follows, In a general way, we can define computing to mean any goal-oriented activity requiring, benefiting from, or creating computers. For example, an information systems specialist will view computing somewhat differently from a software engineer, regardless of the context, doing computing well can be complicated and difficult. Because society needs people to do computing well, we must think of computing not only as a profession, the fundamental question underlying all computing is What can be automated. The term computing is also synonymous with counting and calculating, in earlier times, it was used in reference to the action performed by mechanical computing machines, and before that, to human computers. Computing is intimately tied to the representation of numbers, but long before abstractions like the number arose, there were mathematical concepts to serve the purposes of civilization. These concepts include one-to-one correspondence, comparison to a standard, the earliest known tool for use in computation was the abacus, and it was thought to have been invented in Babylon circa 2400 BC. Its original style of usage was by lines drawn in sand with pebbles, abaci, of a more modern design, are still used as calculation tools today. This was the first known computer and most advanced system of calculation known to date - preceding Greek methods by 2,000 years. The first recorded idea of using electronics for computing was the 1931 paper The Use of Thyratrons for High Speed Automatic Counting of Physical Phenomena by C. E. Wynn-Williams. Claude Shannons 1938 paper A Symbolic Analysis of Relay and Switching Circuits then introduced the idea of using electronics for Boolean algebraic operations, a computer is a machine that manipulates data according to a set of instructions called a computer program. The program has a form that the computer can use directly to execute the instructions. The same program in its source code form, enables a programmer to study. Because the instructions can be carried out in different types of computers, the execution process carries out the instructions in a computer program. Instructions express the computations performed by the computer and they trigger sequences of simple actions on the executing machine. Those actions produce effects according to the semantics of the instructions, computer software or just software, is a collection of computer programs and related data that provides the instructions for telling a computer what to do and how to do it. Software refers to one or more programs and data held in the storage of the computer for some purposes. In other words, software is a set of programs, procedures, algorithms, program software performs the function of the program it implements, either by directly providing instructions to the computer hardware or by serving as input to another piece of software
2.
File system
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In computing, a file system or filesystem is used to control how data is stored and retrieved. Without a file system, information placed in a storage medium would be one large body of data with no way to tell where one piece of information stops, by separating the data into pieces and giving each piece a name, the information is easily isolated and identified. Taking its name from the way paper-based information systems are named, the structure and logic rules used to manage the groups of information and their names is called a file system. There are many different kinds of file systems, each one has different structure and logic, properties of speed, flexibility, security, size and more. Some file systems have been designed to be used for specific applications, for example, the ISO9660 file system is designed specifically for optical discs. File systems can be used on different types of storage devices that use different kinds of media. The most common device in use today is a hard disk drive. Other kinds of media that are used include flash memory, magnetic tapes, in some cases, such as with tmpfs, the computers main memory is used to create a temporary file system for short-term use. Some file systems are used on local storage devices, others provide file access via a network protocol. Some file systems are virtual, meaning that the files are computed on request or are merely a mapping into a different file system used as a backing store. The file system access to both the content of files and the metadata about those files. It is responsible for arranging storage space, reliability, efficiency, before the advent of computers the term file system was used to describe a method of storing and retrieving paper documents. By 1961 the term was being applied to computerized filing alongside the original meaning, by 1964 it was in general use. A file system consists of two or three layers, sometimes the layers are explicitly separated, and sometimes the functions are combined. The logical file system is responsible for interaction with the user application and it provides the application program interface for file operations — OPEN, CLOSE, READ, etc. and passes the requested operation to the layer below it for processing. The logical file system manage open file table entries and per-process file descriptors and this layer provides file access, directory operations, security and protection. The second optional layer is the file system. This interface allows support for multiple concurrent instances of physical file systems, the third layer is the physical file system
3.
Computer file
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A computer file is a computer resource for recording data discretely in a computer storage device. Just as words can be written to paper, so can information be written to a computer file, there are different types of computer files, designed for different purposes. A file may be designed to store a picture, a message, a video. Some types of files can store different several types of information at once, by using computer programs, a person can open, read, change, and close a computer file. Computer files may be reopened, modified, and copied a number of times. Typically, computer files are organised in a system, which keeps track of where the files are. The word file derives from the Latin filum, such a file now exists in a memory tube developed at RCA Laboratories. Electronically it retains figures fed into calculating machines, holds them in storage while it memorizes new ones - speeds intelligent solutions through mazes of mathematics, in 1952, file denoted, inter alia, information stored on punched cards. In early use, the hardware, rather than the contents stored on it, was denominated a file. For example, the IBM350 disk drives were denominated disk files, although the contemporary register file demonstrates the early concept of files, its use has greatly decreased. On most modern operating systems, files are organized into one-dimensional arrays of bytes, for example, the bytes of a plain text file are associated with either ASCII or UTF-8 characters, while the bytes of image, video, and audio files are interpreted otherwise. Most file types also allocate a few bytes for metadata, which allows a file to some basic information about itself. Some file systems can store arbitrary file-specific data outside of the file format, on other file systems this can be done via sidecar files or software-specific databases. All those methods, however, are susceptible to loss of metadata than are container. At any instant in time, a file might have a size, normally expressed as number of bytes, in most modern operating systems the size can be any non-negative whole number of bytes up to a system limit. Many older operating systems kept track only of the number of blocks or tracks occupied by a file on a storage device. In such systems, software employed other methods to track the exact byte count, the general definition of a file does not require that its size have any real meaning, however, unless the data within the file happens to correspond to data within a pool of persistent storage. A special case is a zero byte file, these files can be newly created files that have not yet had any data written to them, or may serve as some kind of flag in the file system, or are accidents
4.
Directory (computing)
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In computing, a directory is a file system cataloging structure which contains references to other computer files, and possibly other directories. On many computers, directories are known as folders, or drawers to provide some relevancy to a workbench or the traditional office file cabinet, files are organized by storing related files in the same directory. In a hierarchical filesystem, a directory contained inside another directory is called a subdirectory, the terms parent and child are often used to describe the relationship between a subdirectory and the directory in which it is cataloged, the latter being the parent. The top-most directory in such a filesystem, which not have a parent of its own, is called the root directory. In modern systems, a directory can contain a mix of files and subdirectories, a reference to a location in a directory system is called a path. In many operating systems, programs have an associated working directory in which they execute, typically, file names accessed by the program are assumed to reside within this directory if the file names are not specified with an explicit directory name. Some operating systems restrict a users access to only their home directory or project directory, in early versions of Unix the root directory was the home directory of the root user, but modern Unix usually uses another directory such as /root for this purpose. In keeping with Unix philosophy, Unix systems treat directories as a type of file, folders are often depicted with icons which visually resemble physical file folders. There is a difference between a directory, which is a file system concept, and the user interface metaphor that is used to represent it. Many operating systems also have the concept of smart folders that reflect the results of a file system search or other operation and these folders do not represent a directory in the file hierarchy. Many email clients allow the creation of folders to organize email and these folders have no corresponding representation in the filesystem structure. If one is referring to a container of documents, the folder is more appropriate. The term directory refers to the way a structured list of document files, operating systems that support hierarchical filesystems implement a form of caching to RAM of recent path lookups. In the Unix world, this is usually called Directory Name Lookup Cache, for local filesystems, DNLC entries normally expire only under pressure from other more recent entries. For network file systems a coherence mechanism is necessary to ensure that entries have not been invalidated by other clients, definition of directory by The Linux Information Project
5.
Filename
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A filename is a name used to uniquely identify a computer file stored in a file system. Different file systems impose different restrictions on filename lengths and the characters within filenames. Discussions of filenames are complicated by a lack of standardisation of the term, sometimes filename is used to mean the entire name, such as the Windows name c, \directory\myfile. txt. Sometimes, it will be used to refer to the components, sometimes, it is a reference that excludes an extension, so the filename would be just myfile. Such ambiguity is widespread and this article does not attempt to define any one meaning, some systems will adopt their own standardised nomenclature like path name, but these too are not standardised across systems. Around 1962, the Compatible Time-Sharing System introduced the concept of a file, around this same time appeared the dot as a filename extension separator, and the limit to three letter extensions might have come from RAD50 16-bit limits. Traditionally, filenames allowed only alphanumeric characters, but as time progressed and this led to compatibility problems when moving files from one file system to another. Around 1995, VFAT, an extension to the FAT filesystem, was introduced in Windows 95 and it allowed mixed-case Unicode long filenames, in addition to classic 8.3 names. In 1985, RFC959 officially defined a pathname to be the string that must be entered into a file system by a user in order to identify a file. One issue was migration to Unicode, for this purpose, several software companies provided software for migrating filenames to the new Unicode encoding. Microsoft provided migration transparent for the user throughout the vfat technology Apple provided File Name Encoding Repair Utility v1.0, Mac OS X10.3 marked Apples adoption of Unicode 3.2 character decomposition, superseding the Unicode 2.1 decomposition used previously. This change caused problems for writing software for Mac OS X. An absolute reference includes all directory levels, in some systems, a filename reference that does not include the complete directory path defaults to the current working directory. One advantage of using a reference in program configuration files or scripts is that different instances of the script or program can use different files. This makes an absolute or relative path composed of a sequence of filenames, Unix-like file systems allow a file to have more than one name, in traditional Unix-style file systems, the names are hard links to the files inode or equivalent. Windows supports hard links on NTFS file systems, and provides the command fsutil in Windows XP, hard links are different from Windows shortcuts, classic Mac OS/macOS aliases, or symbolic links. The introduction of LFNs with VFAT allowed filename aliases, with a maximum of eight plus three characters was a filename alias of long file name. As a way to conform to 8.3 limitations for older programs and this property was used by the move command algorithm that first creates a second filename and then only removes the first filename
6.
Tree structure
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A tree structure or tree diagram is a way of representing the hierarchical nature of a structure in a graphical form. A tree structure is conceptual, and appears in several forms, for a discussion of tree structures in specific fields, see Tree for computer science, insofar as it relates to graph theory, see tree, or also tree. Other related pages are listed below, the tree elements are called nodes. The lines connecting elements are called branches, nodes without children are called leaf nodes, end-nodes, or leaves. Every finite tree structure has a member that has no superior and this member is called the root or root node. The root is the starting node, but the converse is not true, infinite tree structures may or may not have a root node. The names of relationships between nodes model the kinship terminology of family relations, the gender-neutral names parent and child have largely displaced the older father and son terminology, although the term uncle is still used for other nodes at the same level as the parent. A nodes parent is a one step higher in the hierarchy. Sibling nodes share the same parent node, a nodes uncles are siblings of that nodes parent. A node that is connected to all nodes is called an ancestor. The connected lower-level nodes are descendants of the ancestor node, in the example, encyclopedia is the parent of science and culture, its children. Art and craft are siblings, and children of culture, which is their parent, also, encyclopedia, as the root of the tree, is the ancestor of science, culture, art and craft. Finally, science, art and craft, as leaves, are ancestors of no other node, the Oxford English Dictionary records use of both the terms tree structure and tree-diagram from 1965 in Noam Chomskys Aspects of the Theory of Syntax. In a tree there is one and only one path from any point to any other point. Computer science uses tree structures extensively For a formal definition see set theory, internet, usenet hierarchy Document Object Models logical structure, Yahoo. Almost always, these boil down to variations, or combinations, of a few basic styles, Classical node-link diagrams, nested sets that use enclosure/containment to show parenthood, examples include TreeMaps and fractal maps. Layered icicle diagrams that use alignment/adjacency, lists or diagrams that use indentation, sometimes called outlines or tree views. A correspondence to nested parentheses was first noticed by Sir Arthur Cayley, trees can also be represented radially
7.
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
8.
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
9.
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
10.
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
11.
Windows NT 4.0
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Windows NT4.0 is a preemptively multitasked graphical operating system, designed to work with either uniprocessor or symmetric multi-processor computers. It was part of Microsofts Windows NT family of operating systems and was released to manufacturing on 31 July 1996 and it is a 32-bit operating system available in both workstation and server editions with a graphical environment similar to that of Windows 95. It also includes most components introduced with Windows 95, internally, Windows NT4.0 was known as the Shell Update Release. Windows Desktop Update could also be installed on Windows NT4.0 to update the shell version, Windows NT4.0 Resource Kit included the Desktop Themes utility. Windows NT4.0 is the last major release of Microsoft Windows to support the Alpha and it remained in use by businesses for a number of years, despite Microsofts many efforts to get customers to upgrade to Windows 2000 and newer versions. It was also the last release in the Windows NT family to be branded as Windows NT although Windows 2000 carried the designation Built on NT Technology, Windows NT4.0 also introduced the concept of system policies and the System Policy Editor. There are new administrative wizards and a version of the Network Monitor utility shipped with System Management Server. The Enterprise edition introduced Microsoft Cluster Server, one significant difference from previous versions of Windows NT is that the Graphics Device Interface is moved into kernel mode rather than being in user mode in the CSRSS process. This eliminated a process-to-process context switch in calling GDI functions, resulting in a significant performance improvement over Windows NT3.51 and this, however, also mandated that graphics and printer drivers had to run in kernel mode as well, resulting in potential stability issues. Later versions of DirectX were not released for Windows NT4.0, however, OpenGL was supported, it was used by Quake 3 and Unreal Tournament. In early releases of 4.0, numerous stability issues did occur as graphics, Windows NT4.0 also included a new Windows Task Manager utility. Previous versions of Windows NT included the Task List utility, to monitor CPU and memory usage, users were forced to use Performance Monitor. The task manager offers a convenient way of getting a snapshot of all the processes running on the system at any given time. Internet Explorer 2 was bundled with Windows NT4, which updated versions included with each service pack, Service Pack 6, the last service pack for Windows NT4, included Internet Explorer 6 SP1. Windows NT4.0 upgraded NTVDMs x86 emulation in the RISC versions from 286 to 486, sysprep was introduced as a deployment tool with Windows NT4.0. While providing much greater stability than Windows 95, it was less flexible from a desktop perspective, much of the stability was gained through the use of protected memory and the hardware abstraction layer. Direct hardware access was disallowed and misbehaving programs were terminated without needing the computer to be restarted, the trade-off was that NT required much more memory in comparison to consumer targeted products such as Windows 95. While nearly all written for Windows 95 run on Windows NT, many 3D games would not
12.
Windows NT
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Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It is a processor-independent, multiprocessing, multi-user operating system, the first version of Windows NT was Windows NT3.1 and was produced for workstations and server computers. It was intended to complement consumer versions of Windows that were based on MS-DOS, gradually, the Windows NT family was expanded into Microsofts general-purpose operating system product line for all personal computers, deprecating the Windows 9x family. NT was formerly expanded to New Technology but no longer carries any specific meaning, starting with Windows 2000, NT was removed from the product name and is only included in the product version string. NT was the first purely 32-bit version of Windows, whereas its consumer-oriented counterparts, Windows 3. 1x and it is a multi-architecture operating system. Initially, it supported several CPU architectures, including IA-32, MIPS, DEC Alpha, PowerPC, the latest versions support x86 and ARM. This lineage is made clear in Cutlers foreword to Inside Windows NT by Helen Custer and it has been suggested that Dave Cutler intended the initialism WNT as a play on VMS, incrementing each letter by one. However, the project was intended as a follow-on to OS/2 and was referred to as NT OS/2 before receiving the Windows brand. One of the original NT developers, Mark Lucovsky, states that the name was taken from the original target processor—the Intel i860, the letters were dropped from the names of releases from Windows 2000 onwards, though Microsoft described that product as being Built on NT Technology. A main design goal of NT was hardware and software portability, the idea was to have a common code base with a custom Hardware Abstraction Layer for each platform. However, support for MIPS, Alpha, and PowerPC was later dropped in Windows 2000, broad software compatibility was achieved with support for several API personalities, including Windows API, POSIX, and OS/2 APIs – the latter two were phased out starting with Windows XP. Partial MS-DOS compatibility was achieved via an integrated DOS Virtual Machine – although this feature is being phased out in the x86-64 architecture, NT supported per-object access control lists allowing a rich set of security permissions to be applied to systems and services. NT supported Windows network protocols, inheriting the previous OS/2 LAN Manager networking, Windows NT3.1 was the first version of Windows to use 32-bit flat virtual memory addressing on 32-bit processors. Its companion product, Windows 3.1, used segmented addressing, notably, in Windows NT3. x, several I/O driver subsystems, such as video and printing, were user-mode subsystems. In Windows NT4, the video, server, and printer spooler subsystems were moved into kernel mode, NTFS, a journaled, secure file system, was created for NT. Windows NT also allows for other file systems, starting with versions 3.1. Windows NT introduced its own model, the Windows NT driver model. With Windows 2000, the Windows NT driver model was enhanced to become the Windows Driver Model, which was first introduced with Windows 98, but was based on the NT driver model
13.
NTFS
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NTFS is a proprietary file system developed by Microsoft. Starting with Windows NT3.1, it is the file system of Windows NT family. Additional extensions are an elaborate security system based on Access control lists. MacOS kernels also have a limited ability to read NTFS. Linux and BSD kernels have a free and open-source driver for the NTFS filesystem with both read and write functionality, in the mid-1980s, Microsoft and IBM formed a joint project to create the next generation of graphical operating system, the result was OS/2 and HPFS. Because Microsoft disagreed with IBM on many important issues they eventually separated, OS/2 remained an IBM project and Microsoft worked to develop Windows NT, the HPFS file system for OS/2 contained several important new features. When Microsoft created their new operating system, they borrowed many of these concepts for NTFS, NTFS developers include, Tom Miller, Gary Kimura, Brian Andrew and David Goebel. Probably as a result of common ancestry, HPFS and NTFS use the same disk partition identification type code. Using the same Partition ID Record Number is highly unusual, since there were dozens of unused code numbers available, for example, FAT has more than nine. Algorithms identifying the system in a partition type 07 must perform additional checks to distinguish between HPFS and NTFS. Microsoft has released five versions of NTFS, v1.0, v1.0 is incompatible with v1.1 and newer, Volumes written by Windows NT3. 5x cannot be read by Windows NT3.1 until an update is installed. V1.1, Released with Windows NT3.51 in 1995, supports compressed files, named streams and access control lists v1.2, Released with Windows NT4.0 in 1996. Commonly called NTFS4.0 after the OS release, supports disk quotas, Encrypting File System, sparse files, reparse points, update sequence number journaling, the $Extend folder and its files. Reorganized security descriptors so that multiple files using the same security setting can share the same descriptor, commonly called NTFS5.0 after the OS release. V3.1, Released with Windows XP in Autumn,2001, expanded the Master File Table entries with redundant MFT record number. Commonly called NTFS5.1 after the OS release The NTFS. sys version number is based on the system version. Although subsequent versions of Windows added new file system-related features, they did not change NTFS itself, for example, Windows Vista implemented NTFS symbolic links, Transactional NTFS, partition shrinking, and self-healing. NTFS symbolic links are a new feature in the file system, NTFS is optimized for 4 kB clusters, but supports a maximum cluster size of 64 kB
14.
Unix-like
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A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like application is one that behaves like the corresponding Unix command or shell, there is no standard for defining the term, and some difference of opinion is possible as to the degree to which a given operating system or application is Unix-like. The Open Group owns the UNIX trademark and administers the Single UNIX Specification and they do not approve of the construction Unix-like, and consider it a misuse of their trademark. Other parties frequently treat Unix as a genericized trademark, in 2007, Wayne R. Gray sued to dispute the status of UNIX as a trademark, but lost his case, and lost again on appeal, with the court upholding the trademark and its ownership. Unix-like systems started to appear in the late 1970s and early 1980s, many proprietary versions, such as Idris, UNOS, Coherent, and UniFlex, aimed to provide businesses with the functionality available to academic users of UNIX. These largely displaced the proprietary clones, growing incompatibility among these systems led to the creation of interoperability standards, including POSIX and the Single UNIX Specification. Various free, low-cost, and unrestricted substitutes for UNIX emerged in the 1980s and 1990s, including 4. 4BSD, Linux, some of these have in turn been the basis for commercial Unix-like systems, such as BSD/OS and OS X. The various BSD variants are notable in that they are in fact descendants of UNIX, however, the BSD code base has evolved since then, replacing all of the AT&T code. Since the BSD variants are not certified as compliant with the Single UNIX Specification, dennis Ritchie, one of the original creators of Unix, expressed his opinion that Unix-like systems such as Linux are de facto Unix systems. Eric S. Raymond and Rob Landley have suggested there are three kinds of Unix-like systems, Genetic UNIX Those systems with a historical connection to the AT&T codebase. Most commercial UNIX systems fall into this category, so do the BSD systems, which are descendants of work done at the University of California, Berkeley in the late 1970s and early 1980s. Some of these systems have no original AT&T code but can trace their ancestry to AT&T designs. Trademark or branded UNIX These systems—largely commercial in nature—have been determined by the Open Group to meet the Single UNIX Specification and are allowed to carry the UNIX name, many ancient UNIX systems no longer meet this definition. Around 2001, Linux was given the opportunity to get a certification including free help from the POSIX chair Andrew Josey for the price of one dollar. Some non-Unix-like operating systems provide a Unix-like compatibility layer, with degrees of Unix-like functionality. IBM z/OSs UNIX System Services is sufficiently complete to be certified as trademark UNIX, cygwin and MSYS both provide a GNU environment on top of the Microsoft Windows user API, sufficient for most common open source software to be compiled and run. Subsystem for Unix-based Applications provides Unix-like functionality as a Windows NT subsystem, Windows Subsystem for Linux provides a Linux-compatible kernel interface developed by Microsoft and containing no Linux code, with Ubuntu user-mode binaries running on top of it
15.
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
16.
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
17.
Windows Vista
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Windows Vista is an operating system by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs and media center PCs. Development was completed on 8 November 2006, and over the three months, it was released in stages to computer hardware and software manufacturers, business customers. On 30 January 2007, it was released worldwide and was available for purchase. It was succeeded by Windows 7, which was released to manufacturing on 22 July 2009, Vista aimed to increase the level of communication between machines on a home network, using peer-to-peer technology to simplify sharing files and media between computers and devices. Windows Vista included version 3.0 of the. NET Framework, Microsofts primary stated objective with Windows Vista was to improve the state of security in the Windows operating system. One common criticism of Windows XP and its predecessors was their commonly exploited security vulnerabilities and overall susceptibility to malware, viruses, Microsoft stated that it prioritized improving the security of Windows XP and Windows Server 2003 above finishing Windows Vista, thus delaying its completion. While these new features and security improvements have garnered positive reviews, Vista has also been the target of much criticism, as a result of these and other issues, Windows Vista had seen initial adoption and satisfaction rates lower than Windows XP. In May 2010, Windows Vistas market share had a range from 15% to 26%. On 22 October 2010, Microsoft ceased sales of copies of Windows Vista. As of March 2017, Vistas market share was 0. 72%, Microsoft stopped providing mainstream support for Windows Vista on 10 April 2012. Extended support will end on 11 April 2017, Microsoft began work on Windows Vista, known at the time by its codename Longhorn, in May 2001, five months before the release of Windows XP. It was originally expected to ship sometime late in 2003 as a step between Windows XP and Blackcomb, which was planned to be the companys next major operating system release. Gradually, Longhorn assimilated many of the important new features and technologies slated for Blackcomb, in some builds of Longhorn, their license agreement said For the Microsoft product codenamed Whistler. Many of Microsofts developers were also re-tasked to build updates to Windows XP, faced with ongoing delays and concerns about feature creep, Microsoft announced on 27 August 2004, that it had revised its plans. Longhorn became known as Vista in 2005, the early development stages of Longhorn were generally characterized by incremental improvements and updates to Windows XP. After several months of relatively little news or activity from Microsoft with Longhorn, Microsoft released Build 4008 and it was also privately handed out to a select group of software developers. An optional new taskbar was introduced that was thinner than the previous build, the most notable visual and functional difference, however, came with Windows Explorer. The incorporation of the Plex theme made blue the dominant color of the entire application, the Windows XP-style task pane was almost completely replaced with a large horizontal pane that appeared under the toolbars
18.
Dynamic-link library
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Dynamic-link library is Microsofts implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems. These libraries usually have the file extension DLL, OCX, or DRV, the file formats for DLLs are the same as for Windows EXE files – that is, Portable Executable for 32-bit and 64-bit Windows, and New Executable for 16-bit Windows. As with EXEs, DLLs can contain code, data, and resources, data files with the same file format as a DLL, but with different file extensions and possibly containing only resource sections, can be called resource DLLs. Examples of such DLLs include icon libraries, sometimes having the extension ICL, the first versions of Microsoft Windows ran programs together in a single address space. Every program was meant to co-operate by yielding the CPU to other programs so that the user interface could multitask. All operating-system level operations were provided by the operating system. All higher-level services were provided by Windows Libraries Dynamic Link Library, the Drawing API, Graphics Device Interface, was implemented in a DLL called GDI. EXE, the user interface in USER. EXE. The code in GDI needed to translate drawing commands to operations on specific devices, on the display, it had to manipulate pixels in the frame buffer. When drawing to a printer, the API calls had to be transformed into requests to a printer, although it could have been possible to provide hard-coded support for a limited set of devices, Microsoft chose a different approach. GDI would work by loading different pieces of code, called device drivers, with dynamic linking, shared code is placed into a single, separate file. The programs that call this file are connected to it at run time, with the operating system, for those early versions of Windows, the DLLs were the foundation for the entire GUI. As such, display drivers were merely DLLs with a. EXE extension and this notion of building up the operating system from a collection of dynamically loaded libraries is a core concept of Windows that persists as of 2015. DLLs provide the benefits of shared libraries, such as modularity. Modularity allows changes to be made to code and data in a single self-contained DLL shared by several applications without any change to the applications themselves, another benefit of modularity is the use of generic interfaces for plug-ins. A single interface may be developed which allows old as well as new modules to be integrated seamlessly at run-time into pre-existing applications and this concept of dynamic extensibility is taken to the extreme with the Component Object Model, the underpinnings of ActiveX. In Windows 1. x,2. x and 3. x, a DLL was only loaded once into this address space, from then on, all programs using the library accessed it. The librarys data was shared across all the programs and this could be used as an indirect form of inter-process communication, or it could accidentally corrupt the different programs. With the introduction of 32-bit libraries in Windows 95 every process runs in its own address space, while the DLL code may be shared, the data is private except where shared data is explicitly requested by the library
19.
Cygwin
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Cygwin is a Unix-like environment and command-line interface for Microsoft Windows. Cygwin provides native integration of Windows-based applications, data, and other resources with applications, software tools. Thus it is possible to launch Windows applications from the Cygwin environment, as well as to use Cygwin tools, Cygwin was originally developed by Cygnus Solutions, which was later acquired by Red Hat. It is free and open software, released under the GNU Lesser General Public License version 3. Today it is maintained by employees of Red Hat, NetApp, programmers have ported many Unix, GNU, BSD and Linux programs and packages to Cygwin, including the X Window System, K Desktop Environment 3, GNOME, Apache, and TeX. Cygwin permits installing inetd, syslogd, sshd, Apache, and other daemons as standard Windows services, allowing Microsoft Windows systems to emulate Unix, Cygwin programs are installed by running Cygwins setup program, which downloads the necessary program and feature package files from repositories on the Internet. Setup can install, update, and remove programs and their source code packages, a complete installation will take in excess of 36 GB of hard disk space, but usable configurations may require as little as 1 or 2 GB. Initial mount-points can be configured in /etc/fstab, which has a similar format as on Unix systems. Filesystems can be mounted in binary mode, or in text mode, Cygwin 1.7 introduced comprehensive support for POSIX locales and many character encodings, whereby the UTF-8 Unicode encoding became the default. Windows file-names and other identifiers, which are encoded as UTF-16, are converted to. Windows drive letters map to a directory, so for example C. The /cygdrive prefix can be changed, Windows network paths of the form \\HOST\SHARE\FILE are mapped to //HOST/SHARE/FILE. Windows paths can also be used directly from Cygwin programs, but many programs do not support them correctly, full-featured /dev and /proc file-systems are provided. /proc/registry provides direct access to the registry. Cygwin supports POSIX symbolic links, representing them as files with the system attribute set. Cygwin 1.5 represented them as Windows Explorer shortcuts, but this has changed for reasons of performance. Cygwin also recognises NTFS junction points and symbolic links and treats them as POSIX symbolic links, the Solaris API for handling access control lists is supported and maps to the Windows NT ACL system. Special formats of /etc/passwd and /etc/group are provided that include pointers to the Windows equivalent SIDs, the fork system call for duplicating a process is fully implemented, but it does not map well to the Windows API
20.
Data corruption
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Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or processing, which introduce unintended changes to the original data. Computer, transmission, and storage systems use a number of measures to provide end-to-end data integrity, in general, when data corruption occurs a file containing that data will produce unexpected results when accessed by the system or the related application. Results could range from a loss of data to a system crash. The image to the right is an image file in which most of the information has been lost. Some programs can give a suggestion to repair the file automatically and it depends on the level of corruption, and the built-in functionality of the application to handle the error. There are various causes of the corruption, there are two types of data corruption associated with computer systems, undetected and detected. Undetected data corruption, also known as silent data corruption, results in the most dangerous errors as there is no indication that the data is incorrect, data corruption can occur at any level in a system, from the host to the storage medium. Data corruption during transmission has a variety of causes, interruption of data transmission causes information loss. Environmental conditions can interfere with data transmission, especially dealing with wireless transmission methods. Heavy clouds can block satellite transmissions, wireless networks are susceptible to interference from devices such as microwave ovens. Hardware and software failure are the two causes for data loss. Background radiation, head crashes, and aging or wear of the storage device fall into the former category, cosmic rays cause most soft errors in DRAM. Some errors go unnoticed, without being detected by the firmware or the host operating system. There are many error sources beyond the disk storage subsystem itself, in 39,000 storage systems that were analyzed, firmware bugs accounted for 5–10% of storage failures. All in all, the rates as observed by a CERN study on silent corruption are far higher than one in every 1016 bits. Webshop Amazon. com has acknowledged similar high data rates in their systems. One problem is hard disk drive capacities have increased substantially. The data corruption rate has always been constant in time
21.
Solid-state drive
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A solid-state drive is a solid-state storage device that uses integrated circuit assemblies as memory to store data persistently. SSD technology primarily uses electronic interfaces compatible with traditional block input/output hard disk drives, additionally, new I/O interfaces like SATA Express and M.2 have been designed to address specific requirements of the SSD technology. SSDs have no moving mechanical components and this distinguishes them from traditional electromechanical magnetic disks such as hard disk drives or floppy disks, which contain spinning disks and movable read/write heads. Compared with electromechanical disks, SSDs are typically resistant to physical shock, run silently. However, while the price of SSDs has continued to decline over time, as of 2015, most SSDs use MLC NAND-based flash memory, which is a type of non-volatile memory that retains data when power is lost. For applications requiring fast access but not necessarily data persistence after power loss, such devices may employ batteries as integrated power sources to retain data for a certain amount of time after external power is lost. SSDs had origins in the 1950s with two similar technologies, magnetic core memory and charged capacitor read-only storage and these auxiliary memory units emerged during the era of vacuum-tube computers, though their use ceased with the introduction of cheaper drum storage units. Later, in the 1970s and 1980s, SSDs were implemented in memory for early supercomputers of IBM, Amdahl, and Cray. In the late 1970s, General Instruments produced an electrically alterable ROM which operated somewhat like the later NAND flash memory, unfortunately, a ten-year life was not achievable and many companies abandoned the technology. In 1976, Dataram started selling a product called Bulk Core, in 1978, Texas Memory Systems introduced a 16 kilobyte RAM solid-state drive to be used by oil companies for seismic data acquisition. The following year, StorageTek developed the first RAM solid-state drive, the Sharp PC-5000, introduced in 1983, used 128-kilobyte solid-state storage cartridges containing bubble memory. In 1984, Tallgrass Technologies Corporation had a backup unit of 40 MB with a solid state 20 MB unit built in. The 20 MB unit could be used instead of a hard drive, in September 1986, Santa Clara Systems introduced BatRam, a 4 megabyte mass storage system expandable to 20 MB using 4 MB memory modules. The package included a battery to preserve the memory chip contents when the array was not powered. 1987 saw the entry of EMC Corporation into the SSD market, however, by 1993, EMC had exited the SSD market. Software-based RAM disks remain in use as of 2016 because they are an order of faster than other technology, though they consume CPU resources. In 1989, the Psion MC400 laptop included four slots for removable storage in the form of flash-based solid-state disk cards, in 1991, SanDisk Corporation created a 20 MB solid state drive which sold for around $1,000. In 1994, STEC, Inc. bought Cirrus Logics flash controller operation, in 1995, M-Systems introduced flash-based solid-state drives
22.
Integer
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An integer is a number that can be written without a fractional component. For example,21,4,0, and −2048 are integers, while 9.75, 5 1⁄2, the set of integers consists of zero, the positive natural numbers, also called whole numbers or counting numbers, and their additive inverses. This is often denoted by a boldface Z or blackboard bold Z standing for the German word Zahlen, ℤ is a subset of the sets of rational and real numbers and, like the natural numbers, is countably infinite. The integers form the smallest group and the smallest ring containing the natural numbers, in algebraic number theory, the integers are sometimes called rational integers to distinguish them from the more general algebraic integers. In fact, the integers are the integers that are also rational numbers. Like the natural numbers, Z is closed under the operations of addition and multiplication, that is, however, with the inclusion of the negative natural numbers, and, importantly,0, Z is also closed under subtraction. The integers form a ring which is the most basic one, in the following sense, for any unital ring. This universal property, namely to be an object in the category of rings. Z is not closed under division, since the quotient of two integers, need not be an integer, although the natural numbers are closed under exponentiation, the integers are not. The following lists some of the properties of addition and multiplication for any integers a, b and c. In the language of algebra, the first five properties listed above for addition say that Z under addition is an abelian group. As a group under addition, Z is a cyclic group, in fact, Z under addition is the only infinite cyclic group, in the sense that any infinite cyclic group is isomorphic to Z. The first four properties listed above for multiplication say that Z under multiplication is a commutative monoid. However, not every integer has an inverse, e. g. there is no integer x such that 2x =1, because the left hand side is even. This means that Z under multiplication is not a group, all the rules from the above property table, except for the last, taken together say that Z together with addition and multiplication is a commutative ring with unity. It is the prototype of all objects of algebraic structure. Only those equalities of expressions are true in Z for all values of variables, note that certain non-zero integers map to zero in certain rings. The lack of zero-divisors in the means that the commutative ring Z is an integral domain
23.
Inode
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The inode is a data structure in a Unix-style file system that describes a filesystem object such as a file or a directory. Each inode stores the attributes and disk block location of the objects data, filesystem object attributes may include metadata, as well as owner and permission data. Directories are lists of names assigned to inodes, a directory contains an entry for itself, its parent, and each of its children. There has been uncertainty on the Linux kernel mailing list as to the reason for designating these as i nodes, the question was brought to Unix pioneer Dennis Ritchie, who replied, In truth, I dont know either. It was just a term that we started to use, thus the i-number is an index in this array, the i-node is the selected element of the array. This pointer is a called the i-number of the file. When the file is accessed, its i-number is used as an index into a table stored in a known part of the device on which the directory resides. The entry found thereby contains the description of the file, also, Maurice J. Bach writes, The term inode is a contraction of the term index node and is commonly used in literature on the UNIX system. A file system relies on data structures about the files, beside the file content, the former are called metadata—data that describe data. Each file is associated with an inode, which is identified by an integer number, Inodes store information about files and directories, such as file ownership, access mode, and file type. On many types of file system implementations, the number of inodes is fixed at file system creation. A typical allocation heuristic for inodes in a system is one percent of total size. The inode number indexes a table of inodes in a location on the device. From the inode number, the file system driver can access the inode contents. A files inode number can be using the ls -i command. The ls -i command prints the i-node number in the first column of the report, some Unix-style file systems such as ReiserFS omit an inode table, but must store equivalent data in order to provide equivalent capabilities. The data may be called stat data, in reference to the system call that provides the data to programs. File names and directory implications, inodes do not contain file names, Unix directories are lists of association structures, each of which contains one filename and one inode number
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.
File descriptor
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In Unix and related computer operating systems, a file descriptor is an abstract indicator used to access a file or other input/output resource, such as a pipe or network socket. File descriptors form part of the POSIX application programming interface, a file descriptor is a non-negative integer, generally represented in the C programming language as the type int. This table records the mode with which the file has been opened, for reading, writing, appending and it also indexes into a third table called the inode table that describes the actual underlying files. To perform input or output, the passes the file descriptor to the kernel through a system call. The process does not have access to the file or inode tables. On Linux, the set of file descriptors open in a process can be accessed under the path /proc/PID/fd/, in Unix-like systems, file descriptors can refer to any Unix file type named in a file system. As well as files, this includes directories, block and character devices, Unix domain sockets. File descriptors can refer to other objects that do not normally exist in the file system, such as anonymous pipes. The FILE data structure in the C standard I/O library usually includes a low level file descriptor for the object in question on Unix-like systems, the overall data structure provides additional abstraction and is instead known as a file handle. The following lists typical operations on file descriptors on modern Unix-like systems, most of these functions are declared in the <unistd. h> header, but some are in the <fcntl. h> header instead. The fcntl function is used to various operations on a file descriptor. There are commands to get and set attributes associated with a descriptor, including F_GETFD, F_SETFD. The purpose of new operations is to defend against a certain class of TOCTTOU attacks. Openat faccessat fchmodat fchownat fstatat futimesat linkat mkdirat mknodat readlinkat renameat symlinkat unlinkat mkfifoat fdopendir Unix file descriptors behave in ways as capabilities. They can be passed between processes across Unix domain sockets using the system call. Note, however, that what is actually passed is a reference to an open file description that has mutable state, in operating systems that are specifically designed as capability systems, there is very rarely any mutable state associated with a capability itself. A Unix process file descriptor table is an example of a C-list
26.
Emacs
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Emacs /ˈiːmæks/ and its derivatives are a family of text editors that are characterized by their extensibility. The manual for the most widely used variant, GNU Emacs, describes it as the extensible, customizable, self-documenting, development of the first Emacs began in the mid-1970s and continues actively as of 2017. Emacs has over 2,000 built-in commands and allows the user to combine these commands into macros to automate work, Emacs Lisp provides a deep extension capability allowing users and developers to write new commands using a dialect of the Lisp programming language. Extensions have been written to manage email, files, outlines, the original EMACS was written in 1976 by David A. Moon and Guy L. Steele, Jr. as a set of Editor MACroS for the TECO editor. It was inspired by the ideas of the TECO-macro editors TECMAC, the most popular, and most ported, version of Emacs is GNU Emacs, which was created by Richard Stallman for the GNU Project. XEmacs is a variant that branched from GNU Emacs in 1991, both GNU Emacs and XEmacs use Emacs Lisp and are for the most part compatible with each other. Emacs is, along with vi, one of the two contenders in the traditional editor wars of Unix culture. Both are among the oldest application programs still in use, unlike most modern text editors, TECO used separate modes in which the user would either add text, edit existing text, or display the document. This behavior is similar to that of the program ed. Richard Stallman visited the Stanford AI Lab in 1972 or 1974 and saw the labs E editor and he was impressed by the editors intuitive WYSIWYG behavior, which has since become the default behavior of most modern text editors. Stallman reimplemented this mode to run efficiently and then added a feature to the TECO display-editing mode that allowed the user to redefine any keystroke to run a TECO program. E had another feature that TECO lacked, random-access editing, TECO was a page-sequential editor that was designed for editing paper tape on the PDP-1 and typically allowed editing on only one page at a time, in the order of the pages in the file. Almost all modern editors use this approach, the new version of TECO quickly became popular at the AI Lab and soon accumulated a large collection of custom macros whose names often ended in MAC or MACS, which stood for macro. Two years later, Guy Steele took on the project of unifying the overly diverse macros into a single set, Steele and Stallmans finished implementation included facilities for extending and documenting the new macro set. The resulting system was called EMACS, which stood for Editing MACroS or, alternatively, Stallman picked the name Emacs because <E> was not in use as an abbreviation on ITS at the time. An apocryphal hacker koan alleges that the program was named after Emack & Bolios, the first operational EMACS system existed in late 1976. Stallman saw a problem in too much customization and de facto forking and he later wrote, EMACS was distributed on a basis of communal sharing, which means all improvements must be given back to me to be incorporated and distributed. The original Emacs, like TECO, ran only on the PDP-10 running ITS and its behavior was sufficiently different from that of TECO that it could be considered a text editor in its own right, and it quickly became the standard editing program on ITS. Mike McMahon ported Emacs from ITS to the TENEX and TOPS-20 operating systems, other contributors to early versions of Emacs include Kent Pitman, Earl Killian, and Eugene Ciccarelli
27.
UNIX System V
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UNIX System V is one of the first commercial versions of the Unix operating system. It was originally developed by AT&T and first released in 1983, four major versions of System V were released, numbered 1,2,3, and 4. It was the source of common commercial Unix features. System V is sometimes abbreviated to SysV, as of 2012, the Unix market is divided between three System V variants, IBMs AIX, Hewlett-Packards HP-UX and Oracles Solaris. System V was the successor to 1982s UNIX System III, while AT&T sold their own hardware that ran System V, most customers instead ran a version from a reseller, based on AT&Ts reference implementation. A standards document called the System V Interface Definition outlined the default features, in the 1980s and early-1990s, System V was considered one of the two major versions of UNIX, the other being the Berkeley Software Distribution. Historically, BSD was also commonly called BSD Unix or Berkeley Unix, the dispute had several levels, some technical and some cultural. The divide was roughly between longhairs and shorthairs, programmers and technical people tended to line up with Berkeley and BSD, more business-oriented types with AT&T and System V. While HP, IBM and others chose System V as the basis for their Unix offerings, other such as Sun Microsystems. Throughout its development, though, System V was infused with features from BSD, since the early 1990s, due to standardization efforts such as POSIX and the commercial success of Linux, the division between System V and BSD has become less important. System V, known inside Bell Labs as Unix 5.0, there was never an external release of Unix 4.0, which would have been System IV. This first release of System V was developed by AT&Ts UNIX Support Group, System V also included features such as the vi editor and curses from 4.1 BSD, developed at the University of California, Berkeley, it also improved performance by adding buffer and inode caches. It also added support for communication using messages, semaphores. SVR1 ran on DEC PDP-11 and VAX minicomputers, System V Release 2 was released in April,1984. It added shell functions and the SVID, new kernel features included record and file locking, demand paging, and copy on write. The concept of the base was formalized, and the DEC VAX-11/780 was chosen for this release. The porting base is the original version of a release. Educational source licenses for SVR2 were offered by AT&T for US$800 for the first CPU, a commercial source license was offered for $43,000, with three months of support, and a $16,000 price per additional CPU
