A web browser (commonly referred to as a browser) is a software application for accessing information on the World Wide Web. Each individual web page, image, and video is identified by a distinct Uniform Resource Locator (URL), enabling browsers to retrieve these resources from a web server and display them on the user's device.
The web browser works as follows. First, the rendering engine parses CSS and HTML files. While parsing the HTML file, the rendering engine also produces DOM tree data construct where every node refers to an HTML tag, a property or a section of a text. CSS decides the visual style of the webpage based on the style rules, each of which selects single/multiple HTML tags for applying the properties. During parsing, CSS rules are extracted and corresponding data structure is constructed. Based on CSS rules and DOM tree, the style resolution unit decides the style information of the page (such as color font) by generating the render tree. Every node of the render tree corresponds to one visual component of the webpage. From this, the layout unit computes the precise screen-coordinates of every visual component. Finally, the painting unit traverses the render tree and invokes graphics libraries to actually display the page on the screen.
A web browser is not the same thing as a search engine, though the two are often confused. For a user, a search engine is just a website, such as google.com, that stores searchable data about other websites. But to connect to a website's server and display its web pages, a user needs to have a web browser installed on their device.
As of March 2019, more than 4.3 billion people are web browser users, around 55% of the world’s population. Their success is in part caused by their flexibility, due to their Turing-complete execution and powerful graphic capabilities.
The first web browser, called WorldWideWeb, was created in 1990 by Sir Tim Berners-Lee. He then recruited Nicola Pellow to write the Line Mode Browser, which displayed web pages on dumb terminals; it was released in 1991.
1993 was a landmark year with the release of Mosaic, credited as "the world's first popular browser". Its innovative graphical interface made the World Wide Web system easy to use and thus more accessible to the average person. This, in turn, sparked the Internet boom of the 1990s when the Web grew at a very rapid rate. Marc Andreessen, the leader of the Mosaic team, soon started his own company, Netscape, which released the Mosaic-influenced Netscape Navigator in 1994. Navigator quickly became the most popular browser.
Microsoft debuted Internet Explorer in 1995, leading to a browser war with Netscape. Microsoft was able to gain a dominant position for two reasons: it bundled Internet Explorer with its popular Microsoft Windows operating system and did so as freeware with no restrictions on usage. Eventually the market share of Internet Explorer peaked at over 95% in 2002.
In 1998, desperate to remain competitive, Netscape launched what would become the Mozilla Foundation to create a new browser using the open source software model. This work evolved into Firefox, first released by Mozilla in 2004. Firefox reached a 28% market share in 2011.
The last major entrant to the browser market was Google. Its Chrome browser, which debuted in 2008, has been a huge success. It steadily took market share from Internet Explorer and became the most popular browser in 2012. Chrome has remained dominant ever since.
This process begins when the user inputs a URL, such as
https://en.wikipedia.org/, into the browser. Virtually all URLs on the Web start with either
https: which means the browser will retrieve them with the Hypertext Transfer Protocol. In the case of
https:, the communication between the browser and the web server is encrypted for the purposes of security and privacy. Another URL prefix is
file: which is used to display local files already stored on the user's device.
Web pages usually contain hyperlinks to other pages and resources. Each link contains a URL, and when it is clicked, the browser navigates to the new resource. Thus the process of bringing content to the user begins again.
Web browsers can typically be configured with a built-in menu. Depending on the browser, the menu may be named Settings, Options, or Preferences.
The menu has different types of settings. For example, users can change their home page and default search engine. They also can change default web page colors and fonts. Various network connectivity and privacy settings are also usually available.
During the course of browsing, cookies received from various websites are stored by the browser. Some of them contain login credentials or site preferences. However, others are used for tracking user behavior over long periods of time, so browsers typically provide settings for removing cookies when exiting the browser. Finer-grained management of cookies requires a browser extension.
The most popular browsers have a number of features in common. They allow users to set bookmarks and browse in a private mode. They also can be customized with extensions, and some of them provide a sync service.
Most browsers have these user interface features:
- Allow the user to open multiple pages at the same time, either in different browser windows or in different tabs of the same window.
- Back and forward buttons to go back to the previous page visited or forward to the next one.
- A refresh or reload button to reload the current page.
- A stop button to cancel loading the page. (In some browsers, the stop button is merged with the reload button.)
- A home button to return to the user's home page.
- An address bar to input the URL of a page and display it.
- A search bar to input terms into a search engine. (In some browsers, the search bar is merged with the address bar.)
Web browsers are installed on almost all computers. As a result, they are popular targets for attackers to exploit vulnerabilities (security holes). Attackers can use these vulnerabilities to steal information, destroy files, and use computers to attack other computers. Common methods to attack browsers include installing Trojan software or spyware. Instead of actively targeting vulnerabilities, attackers often compromise systems passively when a malicious website is visited.
Certain browser features contain commonly exploited vulnerabilities. They include:
- Plug-ins, applications used by browsers, which may contain programming flaws
- Software frameworks like ActiveX, which can increase the attack surface of a system
- Virtual machines such as a Java virtual machine, which can be bypassed with certain applets
- Cookies, which can grant attackers access to websites
- Scripting languages, which are vulnerable to cross-site scripting (XSS)
Methods used to secure web browsers and computers in general include keeping browser software updated, installing and using antivirus software, and avoiding malicious content and website-based exploits.
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- "What is a Browser?". Google (on YouTube). 30 April 2009.
Less than 8% of people who were interviewed on this day knew what a browser was.
- "No-Judgment Digital Definitions: Internet, Search Engine, Browser". Mozilla. 11 October 2017.
Let’s start by breaking down the differences between internet, search engine, and browser. Lots of us get these three things confused with each other.
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