In this remarkable book on computer design, long-known in the field and widely used in manuscript form, Gerrit A. Blaauw and Frederick P. Brooks, Jr.… - Gerrit Blaauw

By architecture I mean 'appearance to the user' - it is the functional specification of the system (its behavioural appearance). By implementation I mean 'internal logical organisation which performs the functions specified by the architecture' and by realisation I mean 'the physical components in which the logical organisation is embodied'.

The term architecture is used here to describe the attributes of a system as seen by the programmer, i.e., the conceptual structure and functional behavior, as distinct from the organization of the data flow and controls, the logical design, and the physical implementation. i. Additional details concerning the architecture,

Blaauw and Brooks first develop a conceptual framework for understanding computer architecture. They then describe not only what present architectural practice is, but how it came to be so. A major theme is the early divergence and the later reconvergence of computer architectures. They examine both innovations that survived and became part of the standard computer, and the many ideas that were explored in real machines but did not survive. In describing the discards, they also address "why" these ideas did not make it