Edited Page 2 --web Server

Web server The term Web server can mean one of two things: 1. A computer program that is responsible for accepting HTTP requests from clients, which are known as Web browsers, and serving them HTTP responses along with optional data contents, which usually are Web pages such as HTML documents and linked objects (images, etc.). 2. A computer that runs a computer program which provides the functionality described in the first sense of the term.

Common features Although Web server programs differ in detail, they all share some basic common features. 1. HTTP: every Web server program operates by accepting HTTP requests from the network, and providing an HTTP response to the requester. The HTTP response typically consists of an HTML document, but can also be a raw text file, an image, or some other type of document (defined by MIME-types); if something bad is found in client request or while trying to serve the request, a Web server has to send an error response which may include some custom HTML or text messages to better explain the problem to end users. 2. Logging: usually Web servers have also the capability of logging some detailed information, about client requests and server responses, to log files; this allows the Webmaster to collect statistics by running log analyzers on log files. In practice many Web servers implement the following features too. 1. Authentication, optional authorization request (request of user name and password) before allowing access to some or all kind of resources. 2. Handling of not only static content (file content recorded in server's filesystem(s)) but of dynamic content too by supporting one or more related interfaces (SSI, CGI, SCGI, FastCGI, JSP, PHP, ASP, ASP .NET, Server API such as NSAPI, ISAPI, etc.). 3. HTTPS support (by SSL or TLS) to allow secure (encrypted) connections to the server on the standard port 443 instead of usual port 80. 4. Content compression (i.e. by gzip encoding) to reduce the size of the responses (to lower bandwidth usage, etc.). 5. Virtual Hosting to serve many web sites using one IP address. 6. Large file support to be able to serve files whose size is greater than 2 GB on 32 bit OS. 7. Bandwidth throttling to limit the speed of responses in order to not saturate the network and to be able to serve more clients.

Origin of returned content The origin of the content sent by server is called: • •

static if it comes from an existing file lying on a filesystem; dynamic if it is dynamically generated by some other program or script or API called by the Web server.

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.

Performances Web servers (programs) are supposed to serve requests quickly from more than one TCP/IP connection at a time. Main key performance parameters (measured under a varying load of clients and requests per client), are: • • •

number of requests per second (depending on the type of request, etc.); latency time in milliseconds for each new connection or request; throughput in bytes per second (depending on file size, cached or not cached content, available network bandwidth, etc.).

Above three parameters vary noticeably depending on the number of active connections, so a fourth parameter is the concurrency level supported by a Web server under a specific configuration. Last but not least, the specific server model used to implement a Web server program can bias the performance and scalability level that can be reached.

Load limits A web server (program) has defined load limits, because it can handle only a limited number of concurrent client connections (usually between 2 and 60,000, by default between 500 and 1,000) per IP address (and IP port) and it can serve only a certain maximum number of requests per second depending on: • • • • •

its own settings; the HTTP request type; content origin (static or dynamic); the fact that the served content is or is not cached; the hardware and software limits of the OS where it is working.

When a web server is near to or over its limits, it becomes overloaded and thus unresponsive.

Software The most common HTTP serving programs are:[2] • • •

Apache HTTP Server from the Apache Software Foundation. Internet Information Services (IIS) from Microsoft. Sun Java System Web Server from Sun Microsystems.

There are thousands of different Web server programs available, many of which are specialized for very specific purposes, so the fact that a web server is not very popular does not necessarily mean that it has a lot of bugs or poor performance.

Apache HTTP Server Apache HTTP Server Developer: Latest release: OS:

Apache Software Foundation 2.2.4 / January 10, 2007 Cross-platform

Genre:

Web server

License:

Apache License

Website:

http://httpd.apache.org/

The Apache HTTP Server, commonly referred to simply as Apache, is a web server notable for playing a key role in the initial growth of the World Wide Web. Apache was the first viable alternative to the Netscape Communications Corporation web server (currently known as Sun Java System Web Server), and has since evolved to rival other Unix-based web servers in terms of functionality and performance. Since April 1996 Apache has been the most popular HTTP server on the World Wide Web; as of March 2007 Apache served 58% of all websites.[1] The project's name was chosen for two reasons:[2] out of respect for the Native American Indian tribe of Apache (Indé), well-known for their endurance and their skills in warfare,[3] and due to the project's roots as a set of patches to the codebase of NCSA HTTPd 1.3 - making it "a patchy" server.[4]

Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation. The application is available for a wide variety of operating systems including Microsoft Windows, Novell NetWare and Unixlike operating systems such as Linux and Mac OS X. Released under the Apache License, Apache is free and open source software.

History The first version of the Apache web server was created by Robert McCool, who was heavily involved with the National Center for Supercomputing Applications web server, known simply as NCSA HTTPd. When Rob left NCSA in mid-1994, the development of httpd stalled, leaving a variety of patches for improvements circulating through e-mails. Rob McCool was not alone in his efforts. Several other developers helped form the original "Apache Group": Brian Behlendorf, Roy T. Fielding, Rob Hartill, David Robinson, Cliff Skolnick, Randy Terbush, Robert S. Thau, Andrew Wilson, Eric Hagberg, Frank Peters, and Nicolas Pioch. Version 2 of the Apache server was a substantial re-write of much of the Apache 1.x code, with a strong focus on further modularization and the development of a portability layer, the Apache Portable Runtime. The Apache 2.x core has several major enhancements over Apache 1.x. These include UNIX threading, better support for non-Unix platforms (such as Microsoft Windows), a new Apache API, and IPv6 support.[5] The first alpha release of Apache 2 was in March 2000, with the first general availability release on 6 April 2002.[6] Version 2.2 introduced a new authorization API that allows for more flexibility. It also features improved cache modules and proxy modules.[7]

Features Apache supports a variety of features, many implemented as compiled modules which extend the core functionality. These can range from server-side programming language support to authentication schemes. Some common language interfaces support mod_perl, mod_python, Tcl, and PHP. Popular authentication modules include mod_access, mod_auth, and mod_digest. A sample of other features include SSL and TLS support (mod_ssl), a proxy module, a useful URL rewriter (also known as a rewrite engine, implemented under mod_rewrite), custom log files (mod_log_config), and filtering support (mod_include and mod_ext_filter). Apache logs can be analyzed through a web browser using free scripts such as AWStats/W3Perl or Visitors. Virtual hosting allows one Apache installation to serve many different actual websites. For example, one machine, with one Apache installation could simultaneously serve www.example.com, www.test.com, test47.test-server.test.com, etc.

Apache features configurable error messages, DBMS-based authentication databases, and content negotiation. It is also supported by several graphical user interfaces (GUIs) which permit easier, more intuitive configuration of the server.

Usage Apache is primarily used to serve both static content and dynamic Web pages on the World Wide Web. Many web applications are designed expecting the environment and features that Apache provides. Apache is the web server component of the popular LAMP web server application stack, alongside Linux, MySQL, and the PHP/Perl/Python programming languages. Apache is redistributed as part of various proprietary software packages including the Oracle RDBMS or the IBM WebSphere application server. Mac OS X integrates Apache as its built-in web server and as support for its WebObjects application server. It is also supported in some way by Borland in the Kylix and Delphi development tools. Apache is included with Novell NetWare 6.5, where it is the default web server. Apache is used for many other tasks where content needs to be made available in a secure and reliable way. One example is sharing files from a personal computer over the Internet. A user who has Apache installed on their desktop can put arbitrary files in the Apache's document root which can then be shared. Programmers developing web applications often use a locally installed version of Apache in order to preview and test code as it is being developed. Microsoft Internet Information Services (IIS) is the main competitor to Apache, trailed by Sun Microsystems' Sun Java System Web Server and a host of other applications such as Zeus Web Server.

License The software license under which software from the Apache Foundation is distributed is a distinctive part of the Apache HTTP Server's history and presence in the open source software community. The Apache License allows for the distribution of both open and closed source derivations of the source code. The Free Software Foundation does not consider the Apache License to be compatible with version 2.0 of the GNU General Public License (GPL) in that software licensed under the Apache License cannot be integrated with software that is distributed under the GPL: This is a free software license but it is incompatible with the GPL. The Apache Software License is incompatible with the GPL because it has a specific requirement that is not in the GPL: it has certain patent termination cases that the GPL does not require. We don't think those patent

termination cases are inherently a bad idea, but nonetheless they are incompatible with the GNU GPL. —http://www.gnu.org/philosophy/license-list.html

The current draft of Version 3 of the GPL includes a provision (Section 7e) which allows it to be compatible with licenses that have patent retaliation clauses, including the Apache License. The name Apache is a registered trademark and may only be used with the trademark holder's express permission.[8]

Web browser From Wikipedia, the free encyclopedia

A Web browser is a software application that enables a user to display and interact with text, images, and other information typically located on a Web page at a website on the World Wide Web or a local area network. Text and images on a Web page can contain hyperlinks to other Web pages at the same or different website. Web browsers allow a user to quickly and easily access information provided on many Web pages at many websites by traversing these links. Web browsers format HTML information for display, so the appearance of a Web page may differ between browsers. Some of the Web browsers available for personal computers include Internet Explorer, Mozilla Firefox, Safari, Opera, and Netscape in order of descending popularity (as of August 2006).[1] Web browsers are the most commonly used type of HTTP user agent. Although browsers are typically used to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or content in file systems.

Protocols and standards Web browsers communicate with Web servers primarily using HTTP (hypertext transfer protocol) to fetch webpages. HTTP allows Web browsers to submit information to Web servers as well as fetch Web pages from them. The most commonly used HTTP is HTTP/1.1, which is fully defined in RFC 2616. HTTP/1.1 has its own required standards that Internet Explorer does not fully support, but most other current-generation Web browsers do.

Market Share for May, 2007 [2] Internet Explorer - 78.67% Firefox - 14.54% Safari - 4.82% Netscape - 0.83% Opera - 0.74% Opera Mini - 0.16% Mozilla - 0.15%

Pages are located by means of a URL (uniform resource locator, RFC 1738 ), which is treated as an address, beginning with http: for HTTP access. Many browsers also support

a variety of other URL types and their corresponding protocols, such as gopher: for Gopher (a hierarchical hyperlinking protocol), ftp: for FTP (file transfer protocol), rtsp: for RTSP (real-time streaming protocol), and https: for HTTPS (an SSL encrypted version of HTTP). The file format for a Web page is usually HTML (hyper-text markup language) and is identified in the HTTP protocol using a MIME content type. Most browsers natively support a variety of formats in addition to HTML, such as the JPEG, PNG and GIF image formats, and can be extended to support more through the use of plugins. The combination of HTTP content type and URL protocol specification allows Web page designers to embed images, animations, video, sound, and streaming media into a Web page, or to make them accessible through the Web page. Early Web browsers supported only a very simple version of HTML. The rapid development of proprietary Web browsers led to the development of non-standard dialects of HTML, leading to problems with Web interoperability. Modern Web browsers support a combination of standards- and defacto-based HTML and XHTML, which should display in the same way across all browsers. No browser fully supports HTML 4.01, XHTML 1.x or CSS 2.1 yet. Currently many sites are designed using WYSIWYG HTML generation programs such as Macromedia Dreamweaver or Microsoft FrontPage. These often generate non-standard HTML by default, hindering the work of the W3C in developing standards, specifically with XHTML and CSS (cascading style sheets, used for page layout). Some of the more popular browsers include additional components to support Usenet news, IRC (Internet relay chat), and e-mail. Protocols supported may include NNTP (network news transfer protocol), SMTP (simple mail transfer protocol), IMAP (Internet message access protocol), and POP (post office protocol). These browsers are often referred to as Internet suites or application suites rather than merely Web browsers.

Internet Explorer Windows Internet Explorer (formerly Microsoft Internet Explorer, abbreviated MSIE), and commonly abbreviated to IE, is a series of proprietary graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995. After the first release for Windows 95, additional versions of Internet Explorer were developed for other operating systems: Internet Explorer for Mac and Internet Explorer for UNIX (the latter for use through the X Window System on Solaris and HP-UX). Only the Windows version remains in active development; the Mac OS X version is no longer supported.

It has been the most widely used web browser since 1999, peaking at nearly 90% market share with IE6 in the early 2000s—corresponding to over 900 million users worldwide by 2006.[1][2] Though released in 1995 as part of the initial OEM release of Windows 95, Internet Explorer was not included in the first retail, or shrink-wrap, release of Windows 95. The most recent release is version 7.0, which is available as a free update for Windows XP with Service Pack 2, and Windows Server 2003 with Service Pack 1, and is included with Windows Vista. Versions of Internet Explorer prior to 6.0 SP2 are also available as a separate download for versions of Windows prior to Windows XP. An embedded OEM version called Internet Explorer for Windows CE (IE CE) is also available for WinCE based platforms and is currently based on IE6. Another Windows CE/ Windows Mobile browser known as Pocket Internet Explorer is from a different codebase and should not be confused with desktop versions of the browser. Main article: History of Internet Explorer Internet Explorer was originally derived primarily from Spyglass, Inc. Mosaic, an early commercial proprietary web browser. In 1995, Microsoft licensed Spyglass Mosaic from Spyglass for a quarterly fee plus a percentage of Microsoft's revenues for the software. Although bearing a name similar to NCSA Mosaic, which was the first widely used browser, Spyglass Mosaic was relatively unknown in its day and used the NCSA Mosaic source code only sparingly.[3]

Versions 1, 2, and 3 Browser Market Share in May 2007[4][5]

Internet Explorer, All Versions

78.67%

Internet Explorer 4

0.01%

Internet Explorer 5.0

0.28%

Internet Explorer 5.5

0.23%

Internet Explorer 6

46.76%

Internet Explorer 7

31.26%

Netscape (web browser) Jump to: navigation, search Netscape is the general name for a series of web browsers originally produced by Netscape Communications Corporation, now a subsidiary of AOL. The original browser was once the dominant browser in terms of usage share, but as a result of the first browser war it lost virtually all of its share to Internet Explorer. Netscape Navigator 4.08 Main article: Netscape Navigator Netscape Navigator was the name of Netscape's web browser from versions 1.0–4.8. The first beta release versions of the browser were released in 1994 and known as Mosaic and then Mosaic Netscape until a legal challenge from the National Center for Supercomputing Applications (makers of NCSA Mosaic), which many of Netscape's founders used to develop, led to the name change to Netscape Navigator. The company's name also changed from Mosaic Communications Corporation to Netscape Communications Corporation. The browser was easily the most advanced available and was therefore an instant success, becoming market leader while still in beta. Netscape's feature-count and market share continued to grow rapidly after version 1.0 was released. Version 2.0 added a full mail reader called Netscape Mail, thus transforming Netscape from a mere web browser to an Internet suite. During this period, both the browser and the suite were known as Netscape Navigator. Around the same time, AOL started bundling their software with Microsoft's Internet Explorer. Version 3.0 of Netscape (the first beta was codenamed "Atlas") was the first to face any serious competition in the form of Microsoft Internet Explorer 3.0. Netscape, however, easily held off Microsoft's challenge and remained the number one browser for the time being. Version 3.0 was also available in a "Gold" version which featured a WYSIWYG HTML editor (later added to Netscape Communicator as a standard feature). Netscape 3.0 introduced many new features such as new plugins, background colors for tables, the archive attribute and the applet element. Netscape Navigator 3 was a huge success and the undisputed Web Browser giant in its time. The latest version is 3.04.