The Working Memory Model (Baddeley and Hitch 1974) elaborated on Shiffrin and Atkinsons Multi store memory model, describing memory as a flow of information, They argued that Short term memory isn't a unitary store but rather separated into different stores.
The Central Executive: Is in charge of the other slave systems.
The Visuo Spatial Sketch pad: deals with both Visual and Spatial information. (inner eye and inner scribe)
The Phonological loop: (this separates into two sub stores) (inner ear and inner voice)
The Phonological store: A speech based storage system.
The Articulatory system: works on rehearsal within the store.
Eventually the Episodic buffer was introduced (2000): this integrates information into the Long Term Memory.
Baddeley and Hitchs Working Memory Model is supported by various study's (as shown above) and is a much more detailed and accurate description of short term memory than that supplied by Shiffrin and Atkinson. However, it's description of the central executive is extremly simplistic and it's reliability can be questioned as the model doesn't fully explain what it is and does.