IIS creating two instances of code running in Visual Studio

When you run your website from Visual Studio in debug mode, a browser will open "localhost:55471" and IIS express will host the site on your local machine. If you open a second browser and navigate to the same address "localhost:55471" will IIS express create a second instance of the code running in Visual Studio (kind of like how a regular IIS runs on the server) or will it use the same instance and not create the second instance resulting in only one session for both browsers?