I noticed that so many times and I don’t know why it works like this 
for this example: all this is written in asp, buffering, IIS 7, carrier-class server, full RAM and CPU
As you can see on capture, the main page is executed first, then 3 ajax scripts are invoked with jQuery.
I had to call the first message before the document.ready event in order to reply to it up to 2 others.
Otherwise, if 3 is called at the same time, they will not receive a response until the execution of the slowest one is completed. The last 2 are called in document.ready. We clearly see that 2 begin to react when the execution of the slowest is completed. But the lightest of them would be very fast, a few ms.
This also happens when downloading some files from the application. The application sends files using the bynarystream method. When a file is downloaded from the browser client, the application will not respond to any other browser request (for example, on another tab) until the download is complete.
It is strange that you can open another browser (IE, Chrome ...), and the server will immediately respond to any request, but it will act the same for this new browser. No requests from this browser can be executed in parallel.
I know ASP is old stuff, but can someone tell me why it works this way?
Is it due to limitations or browser technologies? due to session mechanism? because of IIS? due to access to the database (I suppose not, because the download is not related to database access when streaming content)? Will it work differently for other languages and environments?
Can I change this behavior? How?
Greetings
Fred