trust enabled motor action responses; in other words, to cognitive functions much closer to what are effected by the human mind.

In our overview of concepts presented by Donald, we have had a cursory look at five distinct memory facilities within the human mind: procedural, episodic, mimetic, mythic and theoretic memories. It is important to note that within the human brain, the elemental unit of information storage has yet to be identified. Computer memory stores strings of bits. For the moment, we do not know the equivalent to a bit in human memory, if the question makes sense. Within human memory there is a significant degree of cognitive capacity that seems inexorably intertwined with the concept of pure memory. The form and processes that these different memory mechanisms support have direct bearing on the cognitive facilities of the human mind. The same situation holds for computer systems, albeit making use of memory mechanisms of different form but with similar application. Many of the end requirements of the cognitive systems are the same in both environments.

Within the human mind, context appears to be an integral aspect of memory. However, at the most basic sensori-motor level of computer systems there exists a need to explicitly establish context. The steps of a stored computer program effect transitions between well-defined states. The interpretation of these states requires a well-defined context; it must be well defined for the central processing unit to execute successive instructions in a meaningful way. At a primitive level within a program, this context tends to be established in one of two ways: either through a set of registers that are loaded with information that defines the context in which an instruction is interpreted and executed, or through a stack. A stack is a sequential series of memory locations into which context information can be loaded. If a specific location within the stack is known, then context information can be positioned relative to this known location. While true, this is context at a much finer level of granularity than we are seeking. In order to draw parallels to human memory, we are interested in establishing the level of context that would allow us to differentiate among mending the wing of our pet parrot, mending the wing of our model airplane or mending the wing of our latest flight of fancy.

To begin to draw the parallels, we can recognize a similar progression in the connection of memory with the facilities of procedural computation in computer systems. These computer mechanisms derived through an evolutionary progression enabled by technological advance and market guidance. In the very earliest machines, there was little external memory associated with the central processing unit of the computer. It had what is often termed main memory in which the controlling stored program was contained and on which this stored program impressed the results of minute state transitions. However, the only means of entering or delivering a large volume of information was through punched cards or punched paper tape. As we have noted previously, these were mechanism more worthy of automated looms than of what we now think of as computers. The point is that the available main memory of the earliest computers had extremely limited space for just storing information.

A stored program might contain a section in which it represents a collection of numbers as something called an array. With a bit of ingenuity, the stored program can be made to efficiently access one particular number in the array by creating an index into the array. Building on this facility, stored programs then evolved to create arrays that could be logically interpreted as doubly indexed collections of numbers. Thus, two dimension arrays and subsequently tables came into being. It is relatively straightforward to relate these mechanisms to the purely procedural memory facilities of the brain considered by Donald. Note that before arrays or tables are of much use within an operational stored program, actual information must somehow be placed into them. That

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