A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by buses, often made of groups of wires.
Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a “1”, and when off it represents a “0” (in positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits.
The control unit, ALU, and registers are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (28 = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two’s complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.
The CPU (central processing unit) contains a special set of memory cells called registers that can be read and written too much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer’s speed.
Computer main memory comes in two principal varieties:
A computer is a general purpose device that can be programmed to carry out a set of arithmeticor logical operations automatically. Since a sequence of operations can be readily changed, the computer can solve more than one kind of problem.
Conventionally, a computer consists of at least one processing element, typically a central processing unit (CPU), and some form of memory. The processing element carries out arithmetic and logic operations, and a sequencing and control unit can change the order of operations in response to stored information. Peripheral devices allow information to be retrieved from an external source, and the result of operations saved and retrieved.
A computer monitor or a computer display is an electronicvisual display for computers. A monitor usually comprises the display device, circuitry, casing, and power supply. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) or a flat panel LED display, while older monitors used a cathode ray tubes (CRT). It can be connected to the computer via VGA, DVI, HDMI, DisplayPort, Thunderbolt, LVDS(Low-voltage differential signaling) or other proprietary connectors and signals.
Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and computer monitors, has changed from 4:3 to 16:10, to 16:9.
In computing, a computer keyboardis a typewriter-style device which uses an arrangement of buttons or keysto act as a mechanical lever or electronic switch. Following the decline of punch cards and paper tape, interaction via teleprinter-style keyboards became the main input device for computers.
A keyboard typically has characters engraved or printedon the keys and each press of a key typically corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce letters, numbersor signs (characters), other keys or simultaneous key presses can produce actions or execute computer commands.
Despite the development of alternative input devices, such as the mouse, touchscreen, pen devices, character recognition and voice recognition, the keyboard remains the most commonly used device for direct (human) input of alphanumericdata into computers.
A computer mouse is a pointing device (hand control) that detects two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer on a display, which allows a smooth control of the graphical user interface.
Physically, a mouse consists of an object held in one’s hand, with one or more buttons. Mice often also feature other elements, such as touch surfaces and “wheels”, which enable additional control and dimensional input.
A computer networkor data network is a telecommunications networkwhich allows computersto exchange data. In computer networks, networked computing devices exchange data with each other using a data link. The connections between nodes are established using either cable media or wireless media. The best-known computer network is the Internet.
Network computer devices that originate, route and terminate the data are called network nodes.Nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other.
Computer networks differ in the transmission medium used to carry their signals, the communications protocols to organize network traffic, the network’s size, topologyand organizational intent.
Computer networks support an enormous number of applications such as access to the World Wide Web, video, digital audio, shared use of application and storage servers, printers, and fax machines, and use of emailand instant messaging applications as well as many others. In most cases, application-specific communications protocols are layered (i.e. carried as payload) over other more general communications protocols.
A computer program is a collection of instructionsthat performs a specific task when executed by a computer. A computer requires programs to function, and typically executes the program’s instructions in a central processing unit.
A computer program is usually written by a computer programmer in a programming language. From the program in its human-readable form of source code, a compiler can derive machine code—a form consisting of instructions that the computer can directly execute. Alternatively, a computer program may be executed with the aid of an interpreter.
A part of a computer program that performs a well-defined task is known as an algorithm. A collection of computer programs, libraries and related data are referred to as software. Computer programs may be categorized along functional lines, such as application software or system software.
Computer programming (often shortened to programming) is a process that leads from an original formulation of a computingproblem to executablecomputer programs. Programming involves activities such as analysis, developing understanding, generating algorithms, verification of requirements of algorithms including their correctness and resources consumption, and implementation (commonly referred to as coding) of algorithms in a target programming language. Source code is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate performing a specific task or solving a given problem. The process of programming thus often requires expertise in many different subjects, including knowledge of the application domain, specialized algorithms and formal logic.
Related tasks include testing, debugging, and maintaining the source code, implementation of the build system, and management of derived artifacts such as machine code of computer programs. These might be considered part of the programming process, but often the term software development is used for this larger process with the term programming, implementation, or coding reserved for the actual writing of source code. Software engineering combines engineeringtechniques with software developmentpractices.
Computer graphicsare picturesand moviescreated using computers– usually referring to image data created by a computer specifically with help from specialized graphical hardware and software. It is a vast and recent area in computer science.The phrase was coined by computer graphics researchers Verne Hudson and William Fetter of Boeing in 1960. Another name for the field is computer-generated imagery, or simply CGI.
Important topics in computer graphics include user interface design, sprite graphics, vector graphics, 3D modeling, shaders, GPU design, and computer vision, among others. The overall methodology depends heavily on the underlying sciences of geometry, optics, and physics. Computer graphics is responsible for displaying art and image dataeffectively and beautifully to the user, and processing image data received from the physical world. The interaction and understanding of computers and interpretation of data has been made easier because of computer graphics. Computer graphic development has had a significant impact on many types of media and has revolutionized animation, movies, advertising, video games, and graphic design generally.
Computer hardware(or simply hardware in computing contexts) is the collection of physical elements that constitutes a computer system. Computer hardware is the physical parts or components of a computer, such as the monitor, keyboard, computer data storage, hard disk drive (HDD), graphic cards, sound cards, memory (RAM), motherboard, and so on, all of which are tangible physical objects.By contrast, softwareis instructions that can be stored and run by hardware.
Software is any set of machine-readable instructions that directs a computer’s processor to perform specific operations. A combination of hardware and software forms a usable computing system.
Computer software, or simply software, is that part of a computer system that consists of encoded information or computer instructions, in contrast to the physical hardwarefrom which the system is built. The term is roughly synonymous with computer program.
The term “software” was first proposed by Alan Turing and used in this sense by John W. Tukey in 1957. In computer science and software engineering, computer software is all information processed by computer systems, programs and data.
Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media. Computer hardware and software require each other and neither can be realistically used on its own.
At the lowest level, executable code consists of machine language instructions specific to an individual processor—typically a central processing unit (CPU). A machine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state. For example, an instruction may change the value stored in a particular storage location in the computer—an effect that is not directly observable to the user. An instruction may also (indirectly) cause something to appear on a display of the computer system—a state change which should be visible to the user. The processor carries out the instructions in the order they are provided, unless it is instructed to “jump” to a different instruction, or interrupted.
The majority of software is written in high-level programming languages that are easier and more efficient for programmers, meaning closer to a natural language.High-level languages are translated into machine language using a compileror an interpreter or a combination of the two. Software may also be written in a low-level assembly language, essentially, a vaguely mnemonicrepresentation of a machine language using a natural language alphabet, which is translated into machine language using an assembler.
A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name.
Domain names are used in various networking contexts and application-specific naming and addressing purposes. In general, a domain name represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a web site, or the web site itself or any other service communicated via the Internet. In 2015, 294 million domain names had been registered.
Domain names are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains(gTLDs), such as the prominent domains com, info, net, edu, and org, and the country code top-level domains (ccTLDs). Below these top-level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.
The registration of these domain names is usually administered by domain name registrars who sell their services to the public.
A fully qualified domain name(FQDN) is a domain name that is completely specified with all labels in the hierarchy of the DNS, having no parts omitted. Labels in the Domain Name System are case-insensitive, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.
Web hosting service
A web hosting service is a type of Internet hosting service that allows individuals and organizations to make their websiteaccessible via the World Wide Web. Web hosts are companies that provide space on a server owned or leased for use by clients, as well as providing Internetconnectivity, typically in a data center. Web hosts can also provide data center space and connectivity to the Internet for other servers located in their data center, called colocation, also known as Housing in Latin America or France.
The scope of web hosting services varies greatly. The most basic is web page and small-scale file hosting, where files can be uploadedvia File Transfer Protocol (FTP) or a Web interface. The files are usually delivered to the Web “as is” or with minimal processing. Many Internet service providers(ISPs) offer this service free to subscribers. Individuals and organizations may also obtain Web page hosting from alternative service providers. Personal web site hosting is typically free, advertisement-sponsored, or inexpensive. Business web site hosting often has a higher expense depending upon the size and type of the site.
Single page hosting is generally sufficient for personal web pages. A complex site calls for a more comprehensive package that provides databasesupport and application development platforms (e.g. ASP.NET, ColdFusion, Java EE, Perl/Plack, PHP or Ruby on Rails). These facilities allow customers to write or install scripts for applications like forumsand content management. Also, Secure Sockets Layer (SSL) is typically used for websites that wish to keep the data transmitted more secure.
The host may also provide an interface or control panel for managing the Web server and installing scripts, as well as other modules and service applications like e-mail. A web server that does not use a control panel for managing the hosting account, is often referred to as a “headless” server. Some hosts specialize in certain software or services (e.g. e-commerce, blogs, etc.).
World Wide Web
The World Wide Web (WWW) is an information space where documents and other web resources are identified by URLs, interlinked by hypertextlinks, and can be accessed via the Internet.The World Wide Web was invented by English scientist Tim Berners-Lee in 1989. He wrote the first web browser in 1990 while employed at CERNin Switzerland.
It has become known simply as the Web. When used attributively (as in web page, web browser, website, web server, web traffic, web search, web user, web technology, etc.) it is invariably written in lower case. Otherwise the initial capital is often retained (‘the Web’), but lower case is becoming increasingly common (‘the web’).
The World Wide Web was central to the development of the Information Age and is the primary tool billions of people use to interact on the Internet.
Web pages are primarily textdocuments formatted and annotated with Hypertext Markup Language (HTML). In addition to formatted text, web pages may contain images, video, and software components that are rendered in the user’s web browser as coherent pages of multimediacontent. Embedded hyperlinks permit users to navigatebetween web pages. Multiple web pages with a common theme, a common domain name, or both, may be called a website. Website content can largely be provided by the publisher, or interactive where users contribute content or the content depends upon the user or their actions. Websites may be mostly informative, primarily for entertainment, or largely for commercial purposes.