How does iis work

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 8, 2026

Quick Answer: Internet Information Services (IIS) is a flexible, secure web server from Microsoft that runs on Windows systems. First released in 1995 with Windows NT 3.51, IIS 10.5 (2021) supports HTTP/2, TLS 1.3, and processes over 30% of active websites globally. It uses modules like URL Rewrite for routing and integrates with ASP.NET for dynamic content.

Key Facts

First released in 1995 with Windows NT 3.51
IIS 10.5 added in 2021 supports HTTP/2 and TLS 1.3
Processes over 30% of active websites worldwide
Uses modular architecture with over 40 native modules
Integrates with ASP.NET for dynamic web applications

Overview

Internet Information Services (IIS) is Microsoft's web server software designed to host websites, web applications, and services on Windows operating systems. First introduced in 1995 as part of Windows NT 3.51, IIS has evolved through multiple versions, with IIS 10.5 being the latest as of 2021. Historically, IIS gained significant market share during the early 2000s, particularly with the release of IIS 6.0 in 2003, which introduced major security and performance improvements. According to W3Techs, IIS currently powers approximately 30% of all active websites, making it the second most popular web server after Apache. The software is included with Windows Server editions and some Windows client versions, providing a tightly integrated solution for Microsoft-based web hosting environments. IIS supports various web standards and protocols, including HTTP, HTTPS, FTP, FTPS, SMTP, and WebSocket, making it versatile for different hosting scenarios.

How It Works

IIS operates through a modular architecture where core functionality is handled by the HTTP.sys kernel-mode driver, which manages HTTP requests at the operating system level for improved performance. When a request arrives, HTTP.sys routes it to the appropriate application pool—a group of worker processes (w3wp.exe) that isolate applications for stability. IIS uses a configuration system based on XML files (applicationHost.config and web.config) that define settings for sites, applications, and security. Key modules include the URL Rewrite module for routing requests, the Authentication modules for security, and the Output Cache for performance optimization. For dynamic content, IIS integrates with frameworks like ASP.NET through the ISAPI extension, processing server-side code to generate HTML responses. The server also supports FastCGI for running scripts in languages like PHP and Python, making it compatible with diverse web technologies.

Why It Matters

IIS is crucial for organizations relying on Microsoft ecosystems, providing a secure and scalable platform for hosting enterprise web applications, intranets, and cloud services. Its integration with Windows Server features like Active Directory simplifies authentication and management for large deployments. In real-world applications, IIS powers major services such as Microsoft's own websites, SharePoint servers, and numerous corporate portals, handling billions of daily requests. The server's support for modern protocols like HTTP/2 and TLS 1.3 enhances performance and security for e-commerce and sensitive data transactions. Additionally, IIS's modular design allows customization through third-party extensions, fostering innovation in web hosting solutions. Its significance extends to development workflows, where tools like IIS Express enable local testing of ASP.NET applications, streamlining the creation of robust web services.