Mental Models

Before one can really understand operating systems, one must have a clear understanding of how a processor works and how computer hardware aids in the development of operating systems.  That is, one must have a conceptual model of how a computer works.

Mental Models

There is a theory of learning referred to as "mental models" (www.tcd.ie/Psychology/Ruth_Byrne/mental_models/). This theory, which seems evident after one has taught for many years, is that people interpret and try to make sense of their world with the help of mental models of how things work.  For example, a person might try to orient him or herself by noticing where the sun is in the sky at a particular time, based on a mental model that holds that the sun rises in the east and sets in the west.  Of course, the setting of the sun is due to many things: the alignment of the earth on its axis with respect to the sun, the daily rotation of the earth, and where the earth is in its annual orbit around the sun, among other things.  These additional details are not particularly important if one can get his or her bearings straight based on the model "the sun rises in the east and sets in the west."  Many humans and animals have been able to navigate correctly for years without understanding astronomy in depth. That is, to be effective a mental model does not have to be entirely accurate as long as it is functionally correct. 

The more accurate a model is, however, the more effective it will be in helping a person interpret the world.  For example, the mental model "the sun rises in the east and sets in the west" becomes increasingly less functionally correct the farther north or south a person lives from the equator.  The sun does not set at all in the usual sense during some periods of the year in the far north and far south.  This is easily explained by modern astronomy, which provides one with an accurate mental model of this phenomenon.  Still peoples who lived in those regions for centuries were able to develop functional mental models based on seasons and sun location in the sky that helped them properly orient themselves at any time of the year without any knowledge of "the way things really work."

The theory of mental models has profound implications for teaching and learning. One is that an instructor should not focus merely on providing students with correct information, but rather that the focus should also be on providing students with a functionally correct model for processing information commensurate with the level of the student in the curriculum.  For example, every person who has used a computer has begun to develop some understanding (a mental model) of how the computer works: what will happen when the computer is turned on, how the computer responds to input from a mouse, and so forth.  Much of such an initial mental model is likely incorrect and will lead to erroneous conclusions as a student progresses through a computer science curriculum unless the mental model is continuously tuned and revised.

Correcting a deficient mental model is not as easy as it might seem.  There is evidence to suggest that merely providing students with a great lecture on a topic does not necessarily result in the students changing their mental models of a concept in response.  The students may continue to make mistakes in the future if the internal model upon which they formulate answers to questions remains incorrect.  The issue seems to be that students need to be able to recognize when their mental models are wrong and also need to be able to make appropriate changes to those models.  Indeed, this capability may be what distinguishes the truly great minds amongst us: the ability to use new information to reformulate mental models to become more accurate.  If instructors can help students (and themselves!) with this task, they may have accomplished the most important task in teaching and learning.

A Mental Model of a Processor

In order to understand operating systems it is imperative that one have a functional mental model of how a computer works.  We provide one in the next section.