(computer science) A program that processes document requests; it also has a database, which is a repository of data and content.
| Sci-Tech Dictionary: Web server |
(computer science) A program that processes document requests; it also has a database, which is a repository of data and content.
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| Computer Desktop Encyclopedia: Web server |
A computer that delivers Web pages to browsers and other files to applications via the HTTP protocol. It includes the hardware, operating system, Web server software, TCP/IP protocols and site content (Web pages and other files). If the Web server is used internally and not by the public, it may be called an "intranet server."
HTTP Server
"Web server" may refer to just the software and not the entire computer system. In such cases, it refers to the HTTP server (IIS, Apache, etc.) that manages requests from the browser and delivers HTML documents and files in response. It also executes server-side scripts (CGI scripts, JSPs, ASPs, etc.) that provide functions such as database searching and e-commerce.
One Computer or Thousands
A single computer system that provides all the Internet services for a department or a small company would include the HTTP server (Web pages and files), FTP server (file downloads), NNTP server (newsgroups) and SMTP server (mail service). This system with all its services could be called a Web server. In ISPs and large companies, each of these services could be in a separate computer or in multiple computers. A datacenter for a large public Web site could contain hundreds and thousands of Web servers.
Web Servers Are Built Into Everything
Web servers are not only used to deliver Web pages. Web server software is built into numerous hardware devices and functions as the control panel for displaying and editing internal settings. Any network device, such as a router, access point or print server may have an internal Web server (HTTP server), which is accessed by its IP address just like a Web site. Contrast with Web client. See application server and embedded Web server.
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| Accounting Dictionary: Web Server |
Software that manages and controls information at the Web site. The program enables responses to be made to requests for information from Web browsers.
| Wikipedia: Web server |
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A web server is a computer program that delivers (serves) content, such as this web page, using the Hypertext Transfer Protocol. The term web server can also refer to the computer or virtual machine running the program.
Contents |
The primary function of a web server is to deliver web pages (HTML documents) and associated content (e.g. images, style sheets, JavaScripts) to clients. A client, commonly a web browser or web crawler, makes a request for a specific resource using HTTP and, if all goes well, the server responds with the content of that resource. The resource is typically a real file on the server's secondary memory, but this is not necessarily the case and depends on how the web server is implemented.
While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files.
Many generic web servers also support server-side scripting (e.g. Apache HTTP Server and PHP). This means that a script can be executed by the server when a client requests it. Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents. This is referred to as dynamic and static content respectively.
Highly niched web servers can be found in devices such as printers and routers in order to ease administration using a familiar user interface in the form of a web page.
In 1989 Tim Berners-Lee proposed to his employer CERN (European Organization for Nuclear Research) a new project, which had the goal of easing the exchange of information between scientists by using a hypertext system. As a result of the implementation of this project, in 1990 Berners-Lee wrote two programs:
Between 1991 and 1994 the simplicity and effectiveness of early technologies used to surf and exchange data through the World Wide Web helped to port them to many different operating systems and spread their use among lots of different social groups of people, first in scientific organizations, then in universities and finally in industry.
In 1994 Tim Berners-Lee decided to constitute the World Wide Web Consortium to regulate the further development of the many technologies involved (HTTP, HTML, etc.) through a standardization process.
The origin of the content sent by server is known as:
Serving static content is usually much faster (from 2 to 100 times) than serving dynamic content, especially if the latter involves data pulled from a database.
Web servers are able to map the path component of a Uniform Resource Locator (URL) into:
For a static request the URL path specified by the client is relative to the Web server's root directory.
Consider the following URL as it would be requested by a client:
http://www.example.com/path/file.html
The client's web browser will translate it into a connection to www.example.com with the following HTTP 1.1 request:
GET /path/file.html HTTP/1.1 Host: www.example.com
The web server on www.example.com will append the given path to the path of its root directory. On Unix machines, this is commonly /var/www. The result is the local file system resource:
/var/www/path/file.html
The web server will then read the file, if it exists, and send a response to the client's web browser. The response will describe the content of the file and contain the file itself.
A web server (program) has defined load limits, because it can handle only a limited number of concurrent client connections (usually between 2 and 80,000, by default between 500 and 1,000) per IP address (and TCP port) and it can serve only a certain maximum number of requests per second depending on:
When a web server is near to or over its limits, it becomes overloaded and thus unresponsive.
A web server can be either implemented into the OS kernel, or in user space (like other regular applications).
An in-kernel web server (like TUX on Linux or Microsoft IIS on Windows) will usually work faster because, as part of the system, it can directly use all the hardware resources it needs, such as:
Web servers that run in user-mode have to ask the system the permission to use more memory or more CPU resources. Not only these requests to the kernel take time, but they are not always satisfied because the system reserves resources for its own usage and has the responsibility to share hardware resources with all the other running applications.
Also applications cannot access the system internal buffers, which is causing useless buffer copies that create another handicap for user-mode web servers. As a consequence, the only way for a user-mode web server to match kernel-mode performances is to raise the quality of its code to much higher standards than the code used into another web server that runs in the kernel.
This is more difficult under Windows than under Linux where the user-mode overhead is 6 times smaller than under Windows.[1]
At any time web servers can be overloaded because of:
The symptoms of an overloaded web server are:
To partially overcome above load limits and to prevent overload, most popular web sites use common techniques like:
http://images.example.com
http://www.example.com
Given below is a list of top Web server software vendors published in a Netcraft survey in January 2009.
| Vendor | Product | Web Sites Hosted | Percent |
|---|---|---|---|
| Apache | Apache | 108,078,535 | 46.90% |
| Microsoft | IIS | 49,723,999 | 21.58% |
| Tencent | qq.com | 30,069,136 | 13.05% |
| GWS | 13,819,947 | 6.0% | |
| nginx | nginx | 13,813,997 | 5.99% |
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