Baddeley and Hitch’s working memory model suggest that short term memory isn’t a single system but rather an alliance of several temporary memory systems working together. The components of the working memory are, the central executive, phonological loop, visuo-spatial sketch pad (VSS) and the episodic buffer. Each part plays a vital role.
In order for the WMM to work there must be some input which enters your sensory memory. The capacity is very large. The duration for sensory memory is very short up to 2 seconds. If the information receives no attention it gets lost through decay. However if I does get attention it goes into the central executive. The central executive is the key component of the working memory. Its function is to direct attention to particular tasks determining which of the slave systems should be allocated with a certain task. The capacity of the central executive is very limited therefore can’t attend to many things at once. After information enters the central executive depending on what the information is it would enter one of the three slave systems.
One slave system is the phonological loop. Which is further subdivided into the articulatory process which is the inner voice and phonological store which is the inner ear. The phonological loop too has a limited capacity. It deals with auditory information and preserves the order of information. The phonological store holds words we hear like an inner ear. The articulatory process is used for words that are heard or seen. These words are silently repeated like an inner voice. This is a form of maintenance rehearsal.
The second slave system is the visuo-spatial sketchpad. This is used when you have to plan a spatial task like getting from one room to another. Visual and spatial information is temporarily stored here. Visual information is what things look like. Spatial information is the relationship between things. It has been suggested that the visuo-spatial sketchpad can be divided into visual cache and inner scribe which deals with spatial relations.
The third and final slave system is the episodic buffer. The buffer was added by Baddeley in 2000 because he had realised the model needed a general store. The phonological loop and visuo-spatial sketchpad deal with processing and temporary storage of specific kind of information. The central executive has no storage capacity so there is nowhere to hold information that relates to both visual and acoustic information. The episodic buffer much like all of the working memory units has limited capacity. Its job is to integrate information from the central executive, the phonological loop, the visual-spatial sketchpad and also from the long term memory.

Some of the key evidence for the working memory model come from case studies of individuals who have suffered serious brain damage. There are a number of problems with using this. Firstly it doesn’t let the researches make a before and after observation to see if their findings are caused because that’s what everyone is like or it is because of the brain damage. Secondly brain damage is traumatic so it may change behaviour itself. Thirdly you cannot generalise this with the entire population because not everybody is brain damaged.
Supportive evidence comes from Paulesu who found out when participant who were required to store a series of letter or sounds of the letters. He found out that when asked to do different things two different parts of the brain were active. This supports the working memory because it explains that there must be two different stores. Therefore the phonological loop is made from two components. A part that deals with sound and another with visual, so one which is capacity pf the mental rehearsal item.
Research into the phonological loop has suggested that it plays an important role in learning to speak and read as well as understanding spoken language.
One main weakness of the working memory model is the researcher Baddeley himself has pointed out that they still don’t have detailed understanding of the way in which working memory actually works.