Browser concurrent threads

Question

I've been looking around for information on the threading model / count common browsers use.

Specifically I imagine when a browser visits a page it will kick off new threads to download the linked resources (css / images etc.) it needs to render the page. I assume there is a finite limit to the amount of concurrent threads they will use, this would conserve bandwidth for the resources nearer the top of the page so the "above the fold" stuff will render quickly.

Does any one have any information on the size of he thread pools used in specific modern browsers? Also if I've oversimplified their operation please let me know.

Answer 1

Asynchronous downloads do not require separate threads; they're handled by the operating system.

However, browsers do have an upper bound (usually 2, 6, 8, or 15) on the number connections to each domain name. (Firefox) (IE)