low level information needed for the uploading of the files via http and html

[unumpigmank]

I have been studying the process of the file uploading via http. My question is that how the file is upload via ajax and not through full page postbacks. I want to know how the file is transmitted via ajax. I read this article. The article mentioned says this method is not possible if the FormData is not available. But I want to know is there anyother method to make the ajax file upload work on all the browser without using iframe method?