Why was the working memory model designed?

The working memory model was designed in order to add extra knowledge to the short term memory, which shows the short term memory not only as being small and with limited capacity but to expand upon that and show that at one side of the working memory you have the phonological loop (which is to show speech based form information) and the visuo spatial, which is commonly known as the "inner eye" and is for visual coding, which turns our knowledge into pictures. It also tries to show what problems can occur if you have to listen to 2 people talking at once...