“In computer design three levels can be distinguished: architecture, implementation and realisation; for the first of them, the following working definition is given: The architecture of a system can be defined as the functional appearance of the system to the user, its phenomenology.”

—  Gerrit Blaauw

Although the term architecture was introduced only ten years ago in computer technology (Buchholz), the concept of architecture is as old as the use of mechanism by man. When a child is taught to look at a clock, it is taught the architecture of the clock. It is told to observe the position of the short and the long hand and to relate these to the hours and the minutes. Once it can distinguish the architecture from the visual appearance, it can tell time as easily from a wrist watch as from the clock on the church tower.
The inner structure of a system is not considered by the architecture: we do not need to know what makes the clock tick, to know what time it is. This inner structure, considered from a logical point of view, will be called the implementation, and its physical embodiment the realisation.
Source: Computer architecture (1972), p. 154

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Gerrit Blaauw 5
Dutch computer scientist 1924–2018

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“There always is an architecture, whether it is defined in advance - as with modern computers - or found out after the fact - as with many older computers. For architecture is determined by behavior, not by words. Therefore, the term architecture, which rightly implies the notion of the arch, or prime structure, should not be understood as the vague overall idea. Rather, the product of the computer architecture, the principle of operations manual, should contain all detail which the user can know, and sooner or later is bound to know.”

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