Scrolling Background

I have seen this on websites before where the website will be one page. And you have to scroll down our sideways to view the different sections of the website like “about”, “contact” etc. But when you scroll the background scrolls slower than the foreground. King of like how the android phones work when you swipe home screens and the background moves just a little bit. I heard it was done using JavaScript but I have Google my brain off and cannot find much on it. Any help? Please move if I am indeed in the wrong section.

the backgrounds are DIV’s positioned fixed (or absolute)
and the TOP position (and LEFT) is changed depending on the scroll position.

just go to one of those websites and view (steal) source

See every time I view source on one of those websites it looks like there is java script controlling it. I cant even remember one of the sites off the top of my head. Let me look for one.