In 1974, Baddeley & Hitch presented the Working Memory model - a new theory of primary memory, which distinguished itself from previous theories by splitting up the memory store into multiple components.
The Working Memory Model divides primary memory into the following parts:
The Central Executive
A core, supervisory module. The Central Executive controls the flow of information to and from the various slave systems and conscious thought.
The Visuo-Spatial Sketchpad
Split into two parts, the Visuo-Spatial sketchpad is responsible for visual information. For example recalling a journey, or picturing a scene. The Visual Cache interprets information about colour and form (something of an inner eye), and the Inner Scribe arranges visual information in the 'mind's eye'.
The Phonological Loop
This element of Working Memory is responsible for auditory and semantic information. The Phonological Store operates as an inner ear, whilst the Articulatory Process rehearses words to keep them in Working Memory whilst required.
The Episodic Buffer
Not much is known about the Episodic Buffer, but it is assumed that Working Memory must have an interaction with Long Term Memory, and so the Episodic Buffer has been included in the model to represent this function.
Baddeley & Hitch's model has been repeatedly tested and developed over the last few decades and remains the leading theory of primary memory. The model receives empirical support from dual-task studies as well as brain-damage case studies, such as KF.