And if you’re looking for the ‘history of the AS/400′, you should probably start with Wikipedia. See for example IBM Power Systems. Keep in mind that “AS/400″ was only one product generation in System/38-> AS/400-> iSeries-> System i-> IBM Power Systems.
Here is a link to an article using the initial code name of the AS400. It was called SilverLake, http://wiki.midrange.com/index.php/Silverlake