Created in 1998, its name is derived from the World Wide Web, but is not affiliated with the W3C (World Wide Web
Consortium). It is run by Refsnes Data in Norway. W3Schools presents thousands of code examples. By using the TryIt
editor, readers can edit examples and execute the code in a sandbox. W3Schools' examples have been criticized as "ugly and
badly formatted", however their pages were stated as "fast" and properly linked.
As the voice of the U.S. standards and conformity assessment system, the American National Standards Institute (ANSI)
empowers its members and constituents to strengthen the U.S. marketplace position in the global economy while helping to assure
the safety and health of consumers and the protection of the environment.
The Institute oversees the creation, promulgation and use of thousands of norms and guidelines that directly impact
businesses in nearly every sector: from acoustical devices to construction equipment, from dairy and livestock production to
energy distribution, and many more. ANSI is also actively engaged in accreditation - assessing the competence of organizations
determining conformance to standards.
To enhance both the global competitiveness of U.S. business and the U.S. quality of life by promoting and facilitating
voluntary consensus standards and conformity assessment systems, and safeguarding their integrity.
ASCII (About this sound listen) ASS-kee) abbreviated from American Standard Code for Information Interchange, is
a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications
equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional
ASCII is the traditional name for the encoding system; the Internet Assigned Numbers Authority (IANA) prefers the
updated name US-ASCII, which clarifies that this system was developed in the US and based on the typographical symbols
predominantly in use there.
ASCII was developed from telegraph code. Its first commercial use was as a seven-bit teleprinter code promoted by Bell
data services. Work on the ASCII standard began on December 11, 1960, with the first meeting of the American Standards
Association's (ASA) (now the American National Standards Institute or ANSI) X3.2 subcommittee. The first edition of the
standard was published in 1963, underwent a major revision during 1967, and experienced its most recent update
during 1986. Compared to earlier telegraph codes, the proposed Bell code and ASCII were both ordered for more convenient
sorting (i.e., alphabetization) of lists, and added features for devices other than teleprinters.
Originally based on the English alphabet, ASCII encodes 128 specified characters into seven-bit integers as shown by
the ASCII chart above. Ninety-five of the encoded characters are printable: these include the digits 0 to 9, lowercase
letters a to z, uppercase letters A to Z, and punctuation symbols. In addition, the original ASCII specification included 33
non-printing control codes which originated with Teletype machines; most of these are now obsolete.
For example, lowercase i would be represented in the ASCII encoding by binary 1101001 = hexadecimal 69 (i is the ninth
letter) = decimal 105.
The American Standard Code for Information Interchange (ASCII) was developed under the auspices of a committee of the
American Standards Association (ASA), called the X3 committee, by its X3.2 (later X3L2) subcommittee, and later by that
subcommittee's X3.2.4 working group (now INCITS). The ASA became the United States of America Standards Institute
(USASI) and ultimately the American National Standards Institute (ANSI).
With the other special characters and control codes filled in, ASCII was published as ASA X3.4-1963, leaving 28
code positions without any assigned meaning, reserved for future standardization, and one unassigned control code.
There was some debate at the time whether there should be more control characters rather than the lowercase alphabet.
The indecision did not last long: during May 1963 the CCITT Working Party on the New Telegraph Alphabet proposed to assign
lowercase characters to sticks[a] 6 and 7, and International Organization for Standardization TC 97 SC 2 voted during
October to incorporate the change into its draft standard. The X3.2.4 task group voted its approval for the change to ASCII
at its May 1963 meeting. Locating the lowercase letters in sticks[a] 6 and 7 caused the characters to differ in bit
pattern from the upper case by a single bit, which simplified case-insensitive character matching and the construction of
keyboards and printers.
The X3 committee made other changes, including other new characters (the brace and vertical bar characters),
renaming some control characters (SOM became start of header (SOH)) and moving or removing others (RU was removed).
ASCII was subsequently updated as USAS X3.4-1967, then USAS X3.4-1968, ANSI X3.4-1977, and finally,
In mathematics and computer science, an algorithm (is an
unambiguous specification of how to solve a class of problems. Algorithms can perform calculation, data processing and
automated reasoning tasks.
An algorithm is an effective method that can be expressed within a finite amount of space and time and in a
well-defined formal language for calculating a function. Starting from an initial state and initial input (perhaps
empty), the instructions describe a computation that, when executed, proceeds through a finite number of well-defined
successive states, eventually producing "output" and terminating at a final ending state. The transition from one state to
the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate random input.
The concept of algorithm has existed for centuries; however, a partial formalization of what would become the modern
algorithm began with attempts to solve the Entscheidungsproblem (the "decision problem") posed by David Hilbert in 1928.
Subsequent formalizations were framed as attempts to define "effective calculability" or "effective method"; those
formalizations included the Gödel–Herbrand–Kleene recursive functions of 1930, 1934 and 1935, Alonzo Church's lambda calculus
of 1936, Emil Post's "Formulation 1" of 1936, and Alan Turing's Turing machines of 1936–7 and 1939. Giving a formal definition
of algorithms, corresponding to the intuitive notion, remains a challenging problem.
Khan Academy is a non-profit educational organization created in 2006 by educator Salman Khan with a goal of
creating a set of online tools that help educate students. The organization produces short lectures in the form of YouTube
videos. Its website also includes supplementary practice exercises and materials for educators. All resources are available
to users of the website. The website and its content are provided mainly in English, but are also available in other languages
like Spanish, Portuguese, Italian, Russian, Turkish, French, Bengali and Hindi.
Khan Academy's website aims to provide a personalized learning experience, mainly built on the videos which are hosted
on YouTube. The website is meant to be used as a supplement to its videos, because it includes other features such as progress
tracking, practice exercises, and teaching tools. The material can also be accessed through mobile applications.
The videos show a recording of drawings on an electronic blackboard, which are similar to the style of a teacher giving
a lecture. The narrator describes each drawing and how they relate to the material being taught. Nonprofit groups have
distributed offline versions of the videos to rural areas in Asia, Latin America, and Africa. Videos range from all
subjects covered in school and for all grades, Kindergarten to High School.
Khan Academy videos have been translated into many of the world's most popular languages, with many videos dubbed into
the world's top spoken languages. There are close to 20,000 subtitle translations available. Khan Academy offers its platform
in 5 languages: English (en), Spanish (es), Portuguese (pt), French (fr) and Bengali (bn).
It also provides online courses for preparing for standardized tests, including the SAT and MCAT.
In mathematics and mathematical logic, Boolean algebra is the branch of algebra in which the values of the variables
are the truth values true and false, usually denoted 1 and 0 respectively. Instead of elementary algebra where the values of
the variables are numbers, and the prime operations are addition and multiplication, the main operations of Boolean algebra are
the conjunction and denoted as ?, the disjunction or denoted as ?, and the negation not denoted as ¬. It is thus a formalism
for describing logical relations in the same way that ordinary algebra describes numeric relations.
Boolean algebra was introduced by George Boole in his first book The Mathematical Analysis of Logic (1847), and set
forth more fully in his
An Investigation of the Laws of Thought (1854).
According to Huntington, the term "Boolean algebra" was first suggested by Sheffer in 1913.
Boolean algebra has been fundamental in the development of digital electronics, and is provided for in all modern
programming languages. It is also used in set theory and statistics.
Cloud storage is a model of data storage in which the digital data is stored in logical pools, the physical storage
spans multiple servers (and often locations), and the physical environment is typically owned and managed by a hosting company.
These cloud storage providers are responsible for keeping the data available and accessible, and the physical environment
protected and running. People and organizations buy or lease storage capacity from the providers to store user, organization,
or application data.
Cloud storage services may be accessed through a co-located cloud computer service, a web service application
programming interface (API) or by applications that utilize the API, such as cloud desktop storage, a cloud storage gateway or
Web-based content management systems.
Cloud computing is believed to have been invented by Joseph Carl Robnett Licklider in the 1960s with his work on
ARPANET to connect people and data from anywhere at any time.
In 1983, CompuServe offered its consumer users a small amount of disk space that could be used to store any files they
chose to upload.
In 1994, AT&T launched PersonaLink Services, an online platform for personal and business communication and
entrepreneurship. The storage was one of the first to be all web-based, and referenced in their commercials as, "you can think
of our electronic meeting place as the cloud." Amazon Web Services introduced their cloud storage service AWS S3 in 2006,
and has gained widespread recognition and adoption as the storage supplier to popular services such as Smugmug, Dropbox,
Synaptop and Pinterest. In 2005, Box announced an online file sharing and personal cloud content management service for
In telecommunications, a communication protocol is a system of rules that allow two or more entities of a
communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules
syntax, semantics and synchronization of communication and possible error recovery methods. Protocols may be implemented by
hardware, software, or a combination of both.
Communicating systems use well-defined formats (protocol) for exchanging various messages. Each message has an exact
meaning intended to elicit a response from a range of possible responses pre-determined for that particular situation. The
specified behavior is typically independent of how it is to be implemented. Communications protocols have to be agreed upon by
the parties involved. To reach agreement, a protocol may be developed into a technical standard. A programming language
describes the same for computations, so there is a close analogy between protocols and programming languages: protocols are to
communications what programming languages are to computations.
Multiple protocols often describe different aspects of a single communication. A group of protocols designed to work
together are known as a protocol suite; when implemented in software they are a protocol stack.
Internet communication protocols are published by the Internet Engineering Task Force (IETF). The IEEE handles wired
and wireless networking The International Organization for Standardization (ISO) other types. The ITU-T handles
telecommunications protocols and formats for the public switched telephone network (PSTN). As the PSTN and Internet converge,
the standards are also being driven towards convergence.
In cryptography, encryption is the process of encoding a message or information in such a way that only authorized
parties can access it. Encryption does not itself prevent interference, but denies the intelligible content to a would-be
interceptor. In an encryption scheme, the intended information or message, referred to as plaintext, is encrypted using an
encryption algorithm – a cipher – generating ciphertext that can only be read if decrypted. For technical reasons, an
encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is in principle possible to decrypt
the message without possessing the key, but, for a well-designed encryption scheme, considerable computational resources and
skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to
recipients but not to unauthorized users.
Symmetric key / Private key
In symmetric-key schemes, the encryption and decryption keys are the same. Communicating parties must have the same
key before they can achieve secure communication.
In public-key encryption schemes, the encryption key is published for anyone to use and encrypt messages. However, only
the receiving party has access to the decryption key that enables messages to be read. Public-key encryption was first
described in a secret document in 1973; before then all encryption schemes were symmetric-key (also called
A publicly available public key encryption application called Pretty Good Privacy (PGP) was written in 1991 by Phil
Zimmermann, and distributed free of charge with source code; it was purchased by Symantec in 2010 and is regularly updated.
Encryption has long been used by militaries and governments to facilitate secret communication. It is now commonly used
in protecting information within many kinds of civilian systems. For example, the Computer Security Institute reported that in
2007, 71% of companies surveyed utilized encryption for some of their data in transit, and 53% utilized encryption for some of
their data in storage. Encryption can be used to protect data "at rest", such as information stored on computers and storage
devices (e.g. USB flash drives). In recent years, there have been numerous reports of confidential data, such as customers'
personal records, being exposed through loss or theft of laptops or backup drives. Encrypting such files at rest helps protect
them should physical security measures fail. Digital rights management systems, which prevent unauthorized use or reproduction
of copyrighted material and protect software against reverse engineering (see also copy protection), is another somewhat
different example of using encryption on data at rest.
In response to encryption of data at rest, cyber-adversaries have developed new types of attacks. These more recent
threats to encryption of data at rest include cryptographic attacks, stolen ciphertext attacks, attacks on encryption
keys, insider attacks, data corruption or integrity attacks, data destruction attacks, and ransomware attacks. Data
fragmentation and active defense data protection technologies attempt to counter some of these attacks, by
distributing, moving, or mutating ciphertext so it is more difficult to identify, steal, corrupt, or destroy.
Encryption is also used to protect data in transit, for example data being transferred via networks (e.g. the
Internet, e-commerce), mobile telephones, wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic
teller machines. There have been numerous reports of data in transit being intercepted in recent years. Data should also be
encrypted when transmitted across networks in order to protect against eavesdropping of network traffic by unauthorized
Explorer++ is a free and open-source navigational file manager for Microsoft Windows. It features multi-tabbed
panes, bookmarks menu, and a customizable user interface. It can be configured to run portably or use the registry. It can also
be set to replace Windows Explorer as the default file manager.
File Explorer, previously known as Windows Explorer
File Explorer, previously known as Windows Explorer, is a file manager application that is included with releases of the
Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file
systems. It is also the component of the operating system that presents many user interface items on the monitor such as the
taskbar and desktop. Controlling the computer is possible without Windows Explorer running (for example, the File | Run command
in Task Manager on NT-derived versions of Windows will function without it, as will commands typed in a command prompt
Windows Explorer was first included with Windows 95 as a replacement for File Manager, which came with all versions of
Windows 3.x operating systems. Explorer could be accessed by double-clicking the new My Computer desktop icon, or launched from
the new Start Menu that replaced the earlier Program Manager. There is also a shortcut key combination: Windows key + E.
Successive versions of Windows (and in some cases, Internet Explorer) introduced new features and capabilities, removed other
features, and generally progressed from being a simple file system navigation tool into a task-based file management system.
While "Windows Explorer" or "File Explorer" is a term most commonly used to describe the file management aspect of the
operating system, the Explorer process also houses the operating system’s search functionality and File Type associations
(based on filename extensions), and is responsible for displaying the desktop icons, the Start Menu, the Taskbar, and the
Control Panel. Collectively, these features are known as the Windows shell.
After a user logs in, the explorer process is created by userinit process. Userinit performs some initialization of the
user environment (such as running the login script and applying group policies) and then looks in the registry at the Shell
value and creates a process to run the system-defined shell – by default, Explorer.exe. Then Userinit exits. This is why
Explorer.exe is shown by various process explorers with no parent – its parent has exited.
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
and the next begins. 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, each group of data is called a "file". 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 ISO 9660 file system is designed specifically for optical discs.
File systems can be used on numerous different types of storage devices that use different kinds of media. The most
common storage device in use today is a hard disk drive. Other kinds of media that are used include flash memory, magnetic
tapes, and optical discs. In some cases, such as with tmpfs, the computer's main memory (random-access memory, RAM) is used to
create a temporary file system for short-term use.
Some file systems are used on local data storage devices; others provide file access via a network protocol (for
example, NFS, SMB, or 9P clients). Some file systems are "virtual", meaning that the supplied "files" (called virtual files)
are computed on request (e.g. procfs) or are merely a mapping into a different file system used as a backing store. The file
system manages access to both the content of files and the metadata about those files. It is responsible for arranging storage
space; reliability, efficiency, and tuning with regard to the physical storage medium are important design considerations.
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. It provides the application program
interface (API) for file operations — OPEN, CLOSE, READ, etc., and passes the requested operation to the layer below it for
processing. The logical file system "manage[s] open file table entries and per-process file descriptors." This layer
provides "file access, directory operations, [and] security and protection."
The second optional layer is the virtual file system. "This interface allows support for multiple concurrent instances
of physical file systems, each of which is called a file system implementation."
The third layer is the physical file system. This layer is concerned with the physical operation of the storage device
(e.g.disk). It processes physical blocks being read or written. It handles buffering and memory management and is responsible
for the physical placement of blocks in specific locations on the storage medium. The physical file system interacts with the
device drivers or with the channel to drive the storage device.
Note: this only applies to file systems used in storage devices.
File systems allocate space in a granular manner, usually multiple physical units on the device. The file system is
responsible for organizing files and directories, and keeping track of which areas of the media belong to which file and which
are not being used. For example, in Apple DOS of the early 1980s, 256-byte sectors on 140 kilobyte floppy disk used a
This results in unused space when a file is not an exact multiple of the allocation unit, sometimes referred to as
slack space. For a 512-byte allocation, the average unused space is 256 bytes. For 64 KB clusters, the average unused space is
32 KB. The size of the allocation unit is chosen when the file system is created. Choosing the allocation size based on the
average size of the files expected to be in the file system can minimize the amount of unusable space. Frequently the default
allocation may provide reasonable usage. Choosing an allocation size that is too small results in excessive overhead if the
file system will contain mostly very large files.
File system fragmentation occurs when unused space or single files are not contiguous. As a file system is used, files
are created, modified and deleted. When a file is created the file system allocates space for the data. Some file systems permit
or require specifying an initial space allocation and subsequent incremental allocations as the file grows. As files are
deleted the space they were allocated eventually is considered available for use by other files. This creates alternating used
and unused areas of various sizes. This is free space fragmentation. When a file is created and there is not an area of
contiguous space available for its initial allocation the space must be assigned in fragments. When a file is modified such
that it becomes larger it may exceed the space initially allocated to it, another allocation must be assigned elsewhere and the
file becomes fragmented.
Google Drive is a file storage and synchronization service developed by Google. Launched on April 24, 2012, Google Drive
allows users to store files in the cloud, synchronize files across devices, and share files. In addition to a website, Google
Drive offers apps with offline capabilities for Windows and macOS computers, and Android and iOS smartphones and tablets.
Google Drive encompasses Google Docs, Sheets and Slides, an office suite that permits collaborative editing of documents,
spreadsheets, presentations, drawings, forms, and more. Files created and edited through the office suite are saved in Google
Google Drive offers users 15 gigabytes of free storage, with 100 gigabytes, 1 terabyte, 2 terabytes, 10 terabytes, 20
terabytes, and 30 terabytes offered through optional paid plans. Files uploaded can be up to 5 terabytes in size. Users can
change privacy settings for individual files and folders, including enabling sharing with other users or making content public.
On the website, users can search for an image by describing its visuals, and use natural language to find specific files, such
as "find my budget spreadsheet from last December". The website and Android app offer a Backups section to see what Android
devices have data backed up to the service, and a completely overhauled computer app released in July 2017 allows for backing
up specific folders on the user's computer. A Quick Access feature can intelligently predict the files users need.
Google Drive is a key component of G Suite, Google's monthly subscription offering for businesses and organizations. As
part of select G Suite plans, Drive offers unlimited storage, advanced file audit reporting, enhanced administration controls,
and greater collaboration tools for teams.
in the agreements grants the company broad rights to reproduce, use, and create derivative works from content stored on Google
Drive. While the policies also confirm that users retain intellectual property rights, privacy advocates raised concerns that
the licenses grant Google the rights to use the information and data to customize advertising and other services Google
provides. In contrast, other members of the media noted that the agreements were no worse than those of competing cloud storage
services, but that the competition uses "more artful language" in the agreements, and also stated that Google needs the rights
in order to "move files around on its servers, cache your data, or make image thumbnails".
As of March 2017, Google Drive has 800 million active users, and as of September 2015, it has over one million
organizational paying users. As of May 2017, there are over two trillion files stored on the service.
A regular expression, regex or regexp (sometimes called a rational expression) is, in theoretical computer
science and formal language theory, a sequence of characters that define a search pattern. Usually this pattern is then used by
string searching algorithms for "find" or "find and replace" operations on strings.
The concept arose in the 1950s when the American mathematician Stephen Cole Kleene formalized the description of a
regular language. The concept came into common use with Unix text-processing utilities. Since the 1980s, different syntaxes for
writing regular expressions exist, one being the POSIX standard and another, widely used, being the Perl syntax.
Regular expressions are used in search engines, search and replace dialogs of word processors and text editors, in text
processing utilities such as sed and AWK and in lexical analysis. Many programming languages provide regex capabilities,
built-in, or via libraries.
The phrase regular expressions (and consequently, regexes) is often used to mean the specific, standard textual syntax
(distinct from the mathematical notation described below) for representing patterns that matching text need to conform to. Each
character in a regular expression (that is, each character in the string describing its pattern) is understood to be a
metacharacter (with its special meaning), or a regular character (with its literal meaning). For example, in the regex a. a is
a literal character which matches just 'a' and . is a meta character which matches every character except a newline. Therefore,
this regex would match for example 'a ' or 'ax' or 'a0'. Together, metacharacters and literal characters can be used to
identify textual material of a given pattern, or process a number of instances of it. Pattern-matches can vary from a precise
equality to a very general similarity (controlled by the metacharacters). For example, . is a very general pattern, [a-z]
(match all letters from 'a' to 'z') is less general and a is a precise pattern (match just 'a'). The metacharacter syntax is
designed specifically to represent prescribed targets in a concise and flexible way to direct the automation of text processing
of a variety of input data, in a form easy to type using a standard ASCII keyboard.
A very simple case of a regular expression in this syntax would be to locate the same word spelled two different ways
in a text editor, the regular expression seriali[sz]e matches both "serialise" and "serialize". Wildcards could also achieve
this, but are more limited in what they can pattern (having fewer metacharacters and a simple language-base).
The usual context of wildcard characters is in globbing similar names in a list of files, whereas regexes are
usually employed in applications that pattern-match text strings in general. For example, the regex ^[ \t]+|[ \t]+$
matches excess whitespace at the beginning or end of a line. An advanced regex used to match any numeral is
See the Examples section for more examples.
A regex processor translates a regular expression in the above syntax into an internal representation which can be
executed and matched against a string representing the text being searched in. One possible approach is the Thompson's
construction algorithm to construct a nondeterministic finite automaton (NFA), which is then made deterministic and the
resulting deterministic finite automaton (DFA) is run on the target text string to recognize substrings that match the regular
expression. The picture shows the NFA scheme N(s*) obtained from the regular expression s*, where s denotes a simpler regular
expression in turn, which has already been recursively translated to the NFA N(s).
A text editor is a type of program used for editing plain text files. Such programs are sometimes known as "notepad"
software, following the Microsoft Notepad.
Text editors are provided with operating systems and software development packages, and can be used to change
configuration files, documentation files and programming language source code.
Plain text files vs. word processor files
There are important differences between plain text files created by a text editor and document files created by word
processors such as Microsoft Word or WordPerfect.
A plain text file uses a character encoding such as UTF-8 or ASCII to represent numbers, letters, and symbols. The only
non-printing characters in the file that can be used to format the text are newline, tab, and formfeed. Plain text files are
often displayed using a monospace font so horizontal alignment and columnar formatting is sometimes done using space
Word processor documents are generally stored in a binary format to allow for localization and formatted text, such as
boldface, italics and multiple fonts, and to be structured into columns and tables.
Although they are often viewed with formatting, documents using markup languages are stored in plain text files that
contain a combination of human-readable text and markup tags. For example, web pages are plain text with HTML tags to achieve
Word processors were developed to allow formatting of text for presentation on a printed page, while text produced by
text editors is generally used for other purposes, such as input data for a computer program.
When both formats are available, the user must select with care. Saving a plain text file in a word-processor format
adds formatting information that can make the text unreadable by a program that expects plain text. Conversely, saving a
word-processor document as plain text removes any formatting information.
A box of punched cards with several program decks.
Before text editors existed, computer text was punched into cards with keypunch machines. Physical boxes of these thin
cardboard cards were then inserted into a card-reader. Magnetic tape and disk "card-image" files created from such card decks
often had no line-separation characters at all, and assumed fixed-length 80-character records. An alternative to cards was
punched paper tape. It could be created by some teleprinters (such as the Teletype), which used special characters to indicate
ends of records.
The first text editors were "line editors" oriented to teleprinter- or typewriter-style terminals without displays.
Commands (often a single keystroke) effected edits to a file at an imaginary insertion point called the "cursor". Edits were
verified by typing a command to print a small section of the file, and periodically by printing the entire file. In some line
editors, the cursor could be moved by commands that specified the line number in the file, text strings (context) for which to
search, and eventually regular expressions. Line editors were major improvements over keypunching. Some line editors could be
used by keypunch; editing commands could be taken from a deck of cards and applied to a specified file. Some common line
editors supported a "verify" mode in which change commands displayed the altered lines.
When computer terminals with video screens became available, screen-based text editors (sometimes called just "screen
editors") became common. One of the earliest full-screen editors was O26, which was written for the operator console of the
CDC 6000 series computers in 1967. Another early full-screen editor was vi. Written in the 1970s, it is still a standard
editor on Unix and Linux operating systems. Emacs, one of the first open source and free software projects, is another early
full-screen or real-time editor, one that was ported to many systems. A full-screen editor's ease-of-use and speed (compared
to the line-based editors) motivated many early purchases of video terminals.
The core data structure in a text editor is the one that manages the string (sequence of characters) or list of records
that represents the current state of the file being edited. While the former could be stored in a single long consecutive
array of characters, the desire for text editors that could more quickly insert text, delete text, and undo/redo previous edits
led to the development of more complicated sequence data structures. A typical text editor uses a gap buffer, a linked list
of lines (as in PaperClip), a piece table, or a rope, as its sequence data structure.
UTF-8 is a character encoding capable of encoding all 1,112,064 valid code points in Unicode using one to four 8-bit
bytes. The encoding is defined by the Unicode standard, and was originally designed by Ken Thompson and Rob Pike. The
name is derived from Unicode (or Universal Coded Character Set) Transformation Format – 8-bit.
It was designed for backward compatibility with ASCII. Code points with lower numerical values, which tend to occur
more frequently, are encoded using fewer bytes. The first 128 characters of Unicode, which correspond one-to-one with ASCII,
are encoded using a single octet with the same binary value as ASCII, so that valid ASCII text is valid UTF-8-encoded Unicode
as well. Since ASCII bytes do not occur when encoding non-ASCII code points into UTF-8, UTF-8 is safe to use within most
programming and document languages that interpret certain ASCII characters in a special way, such as "/" in filenames, "\" in
escape sequences, and "%" in printf.
Note that the ASCII only figure includes web pages with any declared header if they are restricted to ASCII characters.
UTF-8 has been the dominant character encoding for the World Wide Web since 2009, and as of October 2017 accounts for
89.9% of all Web pages. (The next-most popular multibyte encodings, Shift JIS and GB 2312, have 0.9% and 0.6%
respectively). The Internet Mail Consortium (IMC) recommended that all e-mail programs be able to display and create
mail using UTF-8, and the W3C recommends UTF-8 as the default encoding in XML and HTML.
Today IS the very first day of the rest of your life.