I can't seem to find any information on this anywhere.
Either it's my imagination or the ASP.NET Dev Server (Cassini) cannot handle multiple threads (e.g. multiple requests). Is this correct?
Does IIS Express handle multiple threads?
Yes, functionally speaking, cassini processes one request at a time.
IIS Express is an almost full IIS implementation and will provide expected performance.
来源：https://stackoverflow.com/questions/3261144/asp-net-dev-server-cassini-iis-express-and-multiple-threads