What IIS (Internet Information Services) Is and How It Works

IIS is Microsoft's web server software that runs websites on Windows computers

Internet Information Services (IIS) is a web server made by Microsoft. It receives requests from web browsers, finds the files you ask for, and sends them back to your screen. IIS runs on Windows Server operating systems, which is why you'll see it most often in businesses and organizations that already use Microsoft products.

Think of IIS as the software that sits between your browser and the files stored on a computer. When you type a web address into your browser, that request travels to a server running IIS. IIS figures out which file you want, retrieves it, and sends it back. If the file doesn't exist, IIS sends back an error message instead.

IIS comes built into Windows Server — you don't buy it separately. You turn it on through Windows settings, configure it to point to your website files, and it starts handling requests. Many hosting companies use IIS on their servers, which is why you might encounter it when choosing where to host a website.

Key Takeaways

IIS is Microsoft's web server software that runs on Windows Server and handles requests from web browsers to deliver website files.
IIS comes included with Windows Server and doesn't require a separate purchase, though you do need to enable and configure it.
IIS works well with Microsoft technologies like ASP.NET, SQL Server, and Active Directory, making it common in enterprise environments.
IIS and Apache are the two most widely used web servers, with IIS stronger in Windows-based organizations and Apache more common overall.
Hosting providers offer IIS-based plans if your website needs ASP.NET, Microsoft SQL Server, or other Windows-specific tools.

How IIS receives and responds to browser requests

When someone visits your website, their browser sends an HTTP or HTTPS request to your server's address. IIS listens on port 80 (for HTTP) or port 443 (for HTTPS) — these are like mailboxes where web requests arrive. IIS reads the request, which includes the web address and what the browser is asking for.

IIS then looks for the file in the folder you've told it to use — usually called the "root" folder. If the file exists, IIS sends it back with a 200 status code, which means "success." If the file doesn't exist, IIS sends back a 404 error, which means "not found." IIS can also run code before sending the file back — for example, it can run an ASP.NET program that builds a custom page based on what the browser asked for.

IIS keeps logs of every request it receives. These logs show which files were requested, when, from which computer, and whether the request succeeded or failed. Website owners use these logs to understand how many visitors they get and what pages people look at.

IIS works best with Microsoft's own software and tools

IIS is tightly integrated with Microsoft technologies. If your website runs ASP.NET — Microsoft's framework for building dynamic websites — IIS handles it natively without extra setup. The same is true for Microsoft SQL Server, the database software that stores your website's data. IIS can also connect to Active Directory, which is how large organizations manage user accounts and permissions across many computers.

This integration is one reason large companies choose IIS. If your organization already uses Windows Server, SQL Server, and Active Directory, adding IIS means everything talks to each other smoothly. You don't have to learn a different system or translate between incompatible tools.

If your website uses other languages like PHP or Python, IIS can run them, but it requires extra configuration. Apache, the other major web server, handles these languages more naturally because it was designed to work with them from the start.

IIS versus Apache: the two main web server choices

Apache and IIS are the two most common web servers in use today. Apache runs on Linux, Unix, and Windows. IIS runs only on Windows Server. Because Linux hosting is cheaper than Windows hosting, Apache powers more websites overall — but IIS is still widely used, especially in enterprise settings.

Apache is open-source, meaning anyone can read its code and modify it. IIS is proprietary, meaning only Microsoft controls it. Open-source software often has more community support and more third-party tools built around it, while proprietary software usually has more direct support from the company that made it.

The choice between them usually comes down to what your website needs. If you're building an ASP.NET site or need SQL Server, IIS is the natural choice. If you're using PHP, Python, or Ruby, Apache or Nginx (another popular web server) might be easier. Many hosting companies offer both, so you can choose based on your website's requirements rather than being locked into one option.

What you need to run IIS on your own server

To run IIS, you need a computer running Windows Server — not regular Windows. Windows Server is the version of Windows designed for servers, and it includes IIS as an optional component. You can't run IIS on Windows 10 or Windows 11 (the versions most people use on home computers), though those versions do include a limited version called IIS Express for testing.

Once you have Windows Server installed, you enable IIS through the "Add Roles and Features" tool in Windows. You tell it which version of IIS you want (the latest is IIS 10.0 on Windows Server 2022), and Windows installs it automatically. Then you point IIS to the folder where your website files live, and it starts serving them.

Running your own server requires technical knowledge — you need to understand how to secure it, back it up, update it, and troubleshoot problems. Most small businesses and individuals use a hosting company instead, which handles all of this for you.

Hosting companies that offer IIS-based plans

If you want to host a website on IIS but don't want to run your own server, you can rent space from a hosting company that uses IIS. These companies maintain the servers, handle security updates, and manage backups. You just upload your website files and configure your domain name.

IIS hosting plans typically cost more than Apache hosting plans because Windows Server licenses are more expensive than Linux. A basic IIS hosting plan might cost $10 to $20 per month, while a comparable Apache plan might cost $5 to $10. The price difference reflects the cost of the Windows Server license, not a difference in quality or features.

When you're choosing a hosting company, ask whether they offer IIS and what version. Older versions like IIS 7.5 are still in use but lack security features found in newer versions. Most reputable hosting companies offer at least IIS 10.0, which is current as of 2024.

Common reasons websites use IIS

Organizations choose IIS when they're already invested in Microsoft technology. A company that uses Active Directory for employee accounts, SQL Server for databases, and Office 365 for email will find IIS a natural fit. IIS integrates with all of these without extra work.

IIS is also common in industries with strict compliance requirements. Financial institutions, healthcare organizations, and government agencies often use Windows Server and IIS because they're familiar with how to audit and secure them. The tools for logging, monitoring, and controlling access are well-established.

Some websites use IIS simply because the developer or company knows it well. If your development team has years of experience with ASP.NET and IIS, building on that platform is faster and cheaper than learning Apache and PHP.

Frequently Asked Questions

Can I run IIS on a regular Windows computer?

Not the full version. Windows 10 and Windows 11 include IIS Express, a lightweight version for testing websites during development. For a production website that serves real visitors, you need Windows Server. IIS Express is free and useful for learning, but it's not designed to handle heavy traffic or run continuously.

Is IIS secure?

IIS can be secure if configured correctly, but it requires knowledge. You need to keep Windows Server updated with security patches, disable unnecessary features, set proper file permissions, and use HTTPS. Many security breaches happen because IIS was installed but not properly hardened. Hosting companies handle this for you, which is one reason many people prefer managed hosting.

What's the difference between IIS and a hosting company's web server?

IIS is the software. A hosting company's web server is a physical computer running IIS (or Apache, or Nginx). When you rent hosting, you're renting space on their server, which runs IIS in the background. You don't interact with IIS directly — you just upload files and the hosting company's IIS handles serving them.

Do I need to know IIS to host a website?

Not if you use a hosting company. They manage IIS for you. You only need to know IIS if you're running your own Windows Server, which is rare for small websites. Most people choose a hosting plan and never think about IIS at all.

Can IIS run websites built with PHP or Python?

Yes, but it requires extra setup. IIS can run PHP through an extension and Python through a module, but these languages were designed for Apache and Linux. Running them on IIS works, but Apache or Nginx are more natural choices. If your website uses PHP or Python, ask your hosting company whether they offer Apache hosting — it's usually cheaper and simpler.

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