Internet Information Services (IIS, 2S) is an extensible web server created by Microsoft for use with the Windows NT family. IIS supports HTTP, HTTP/2, HTTPS, FTP, FTPS, SMTP and NNTP. It has been an integral part of the Windows NT family since Windows NT 4.0, though it may be absent from some editions (e.g. Windows XP Home edition), and is not active by default.
History
The first Microsoft web server was a research project at 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 handle the volume of traffic going to Microsoft.com, Microsoft was forced to develop its own web server, IIS.
Almost every version of IIS was released either alongside or with a version of Microsoft Windows: IIS 1.0 was initially released as a free add-on for Windows NT 3.51. IIS 2.0 was included with Windows NT 4.0. IIS 3.0, which was included with Service Pack 2 of Windows NT 4.0, introduced the Active Server Pages dynamic scripting environment. IIS 4.0 was released as part of the "Option Pack" for Windows NT 4.0. It introduced the new MMC-based administration application and also was the first version where multiple instances of web and FTP servers can run, differentiating them by port number and/or hostname. It was also the first version to run application pools. IIS 5.0 shipped with Windows 2000 and introduced additional authentication methods, support for the WebDAV protocol, and enhancements to ASP. IIS 5.0 also dropped support for the Gopher protocol. IIS 5.0 added HTTP.SYS. IIS 5.1 was shipped with Windows XP Professional and was nearly identical to IIS 5.0 on Windows 2000. IIS 6.0 included with Windows Server 2003 and Windows XP Professional x64 Edition, added support for IPv6 and included a new worker process model that increased security as well as reliability. HTTP.sys was introduced in IIS 6.0 as an HTTP-specific protocol listener for HTTP requests. Also each component (like for example Server Side Includes or ASP) now has to be explicitly installed, because in earlier versions often hackers entered sites by using security bugs of components that were not even in use by the hacked site, improving security. IIS 7.0 was a complete redesign and rewrite of IIS and was shipped with Windows Vista and Windows Server 2008. IIS 7.0 included a new modular design that allowed for a reduced attack surface and increased performance. It also introduced a hierarchical configuration system allowing for simpler site deploys, a new Windows Forms-based management application, new command-line management options and increased support for the .NET Framework. IIS 7.0 on Vista does not limit the number of allowed connections as 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 as with XP. IIS 7.5 was included in Windows 7 (but it must be turned on in the side panel of Programs and Features) and Windows Server 2008 R2. IIS 7.5 improved WebDAV and FTP modules as well as command-line administration in PowerShell. It also introduced TLS 1.1 and TLS 1.2 support and the Best Practices Analyzer tool and process isolation for application pools. IIS 8.0 is only available in Windows Server 2012 and Windows 8. IIS 8.0 includes SNI (binding SSL to hostnames rather than IP addresses), Application Initialization, centralized SSL certificate support, and multicore scaling on NUMA hardware, among other new features. IIS 8.5 is included in Windows Server 2012 R2 and Windows 8.1. This version includes Idle worker-Process page-out, Dynamic Site Activation, Enhanced Logging, ETW logging, and Automatic Certificate Rebind. IIS 10.0 version 1607 a.k.a. version 10.0.14393 is included in Windows Server 2016 released 2016-09-26 and Windows 10 Anniversary Update released 2016-08-02. This version includes support for HTTP/2, running IIS in Windows containers on Nano Server, a new Rest management API and corresponding web-based management GUI, and Wildcard Host Headers. IIS 10.0 version 1709 is included in Windows Server, version 1709 (Semi-Annual Channel) and Windows 10 Fall Creators Update both released 2017-10-17. This version adds support for HSTS, container enhancements, new site binding PowerShell cmdlets, and 4 new server variables prefixed with "CRYPT_". IIS 10.0 version 1809 a.k.a. version 10.0.17763 is included in Windows Server 2019 and Windows 10 October Update released 2018-10-02.