1.
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
2.
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
3.
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
4.
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
5.
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
6.
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
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.
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
9.
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
10.
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
11.
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
12.
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
