The number of users that Internet Information Services (IIS) can support concurrently depends on various factors, including the hardware configuration, the specific workload, and the performance optimizations implemented. Here are some considerations:

1. Hardware Resources: The capacity of IIS to handle concurrent users is influenced by the hardware resources available, such as CPU power, memory, and network bandwidth. A more powerful server with sufficient resources can generally handle a larger number of concurrent users.
2. Application Design and Complexity: The design and complexity of the web application hosted on IIS can impact its ability to handle concurrent connections. Efficiently written code, optimized database queries, and caching mechanisms can improve performance and enable better scalability.
3. Configuration and Tuning: Proper configuration and tuning of IIS settings can help optimize its performance. This includes adjusting the maximum concurrent connection limits, managing connection timeouts, and fine-tuning the worker processes and thread pool settings.
4. Network Infrastructure: The capacity of IIS can also be influenced by the network infrastructure, including network bandwidth, load balancing, and firewall settings. A well-configured and robust network infrastructure can better handle concurrent connections.
5. User Behavior: The behavior of users accessing the web application hosted on IIS can also impact its concurrent user capacity. If users perform frequent resource-intensive actions, such as uploading or downloading large files, it may reduce the number of concurrent users that can be effectively supported.

It is challenging to provide an exact number of concurrent users that IIS can support, as it depends on the specific factors mentioned above. In real-world scenarios, the capacity can range from a few hundred to several thousand concurrent users. Load testing and performance profiling specific to your application and infrastructure can provide a better understanding of the concurrent user capacity of your IIS setup.