Assume we have page A and on this page we have a number of elements, including a couple of script and style tags. With synchronous data transfer the script tag needs to be parsed before the next element is parsed. In this way then the next element to be parsed by the browser is dependent upon the script tag being parsed first. Effectively we are creating a bottleneck of one connection between Web page and browser. Style tags and link elements in the head section of the document create the same bottleneck effect. They have to be parsed one at a time before other page elements can download.

Once they have been parsed then the elements in the body section can use concurrent connections to help speed up the download process. For example, most servers handle between 2 to 4 concurrent connections between web page and browser.