Web Servers

A Web server is a program that, using the client/server model and the World Wide Web's Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). Every computer on the Internet that contains a Web site must have a Web server program. Two leading Web servers are Apache, the most widely-installed Web server, and Microsoft's Internet Information Server (IIS). Other Web servers include Novell's Web Server for users of its NetWare operating system and IBM's family of Lotus Domino servers, primarily for IBM's OS/390 and AS/400 customers.
Web servers often come as part of a larger package of Internet- and intranet-related programs for serving e-mail, downloading requests for File Transfer Protocol (FTP) files, and building and publishing Web pages. Considerations in choosing a Web server include how well it works with the operating system and other servers, its ability to handle server-side programming, security characteristics, and publishing, search engine, and site building tools that may come with it.

Apache:

Often referred to as simply Apache, a public-domain open source Web server developed by a loosely-knit group of programmers. The first version of Apache, based on the NCSA httpd Web server, was developed in 1995.
Core development of the Apache Web server is performed by a group of about 20 volunteer programmers, called the Apache Group. However, because the source code is freely available, anyone can adapt the server for specific needs, and there is a large public library of Apache add-ons. In many respects, development of Apache is similar to development of the Linux operating system.
The original version of Apache was written for UNIX, but there are now versions that run under OS/2, Windows and other platforms.
The name is a tribute to the Native American Apache Indian tribe, a tribe well known for its endurance and skill in warfare. A common misunderstanding is that it was called Apache because it was developed from existing NCSA code plus various patches, hence the name a patchy server, or Apache server.

IIS:

Microsoft Internet Information Services (IIS, formerly called Internet Information Server) is a set of Internet-based services for servers using Microsoft Windows. It is the world's second most popular web server in terms of overall websites, behind Apache HTTP Server. As of June 2008 it served 35.39% of all websites according to Netcraft. The servers currently include FTP, SMTP, NNTP, and HTTP/HTTPS.
Versions
• IIS 1.0, Windows NT 3.51 available as a free add-on
• IIS 2.0, Windows NT 4.0
• IIS 3.0, Windows NT 4.0 Service Pack 3
• IIS 4.0, Windows NT 4.0 Option Pack
• IIS 5.0, Windows 2000
• IIS 5.1, Windows XP Professional,Windows MCE
• IIS 6.0, Windows Server 2003 and Windows XP Professional x64 Edition
• IIS 7.0, Windows Server 2008 and Windows Vista



History:

The first Microsoft-endorsed webserver was a research project by the European Microsoft Windows NT Academic Centre (EMWAC), part of the University of Edinburgh in Scotland, and was distributed as freeware. However since the EMWAC server was unable to scale sufficiently to handle the volume of traffic going to microsoft.com, Microsoft was forced to develop its own webserver, IIS.
IIS was initially released as an additional set of Internet based services for Windows NT 3.51. IIS 2.0 followed adding support for the Windows NT 4.0 operating system and IIS 3.0 introduced the Active Server Pages dynamic scripting environment.
IIS 4.0 dropped support for the Gopher protocol and was bundled with Windows NT as a separate "Option Pack" CD-ROM.
The current shipping version of IIS is 7.0 for Windows Vista and Windows Server 2008, 6.0 for Windows Server 2003 and Windows XP Professional x64 Edition, and IIS 5.1 for Windows XP Professional. Windows XP has a restricted version of IIS 5.1 that supports only 10 simultaneous connections and a single web site. IIS 6.0 added support for IPv6. A FastCGI module is also available for IIS5.1, IIS6 and IIS7.
Windows Vista does not install IIS 7.0 by default, but it can be selected among the list of optionally installed components. IIS 7.0 is available in all editions of Windows Vista except Home Basic and Starter. IIS 7 on Vista does not limit the number of allowed connections, like IIS on XP did, but limits concurrent requests to 10 (Windows Vista Ultimate, Business, and Enterprise Editions) or 3 (Vista Home Premium). Additional requests are queued which hampers performance but they are not rejected like in XP which resulted in the 'server too busy' error message.