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Computer architecture refers to those attributes or features of a system visible to a programmer. This view includes aspects such as the sizes of data types (e.g. using 16 binary digits to represent an integer), and the types of operations that are supported (like addition, subtraction, and subroutine calls). In other words, it refers to those attributes that have a direct impact on the logical execution of a program. It includes instruction formats, the instruction set, the number of bits used to represent various data types (e.g. number, character), I/O mechanisms and techniques of addressing memory.

There is a concept of levels in computer architecture. The basic idea is that there are many levels, or views, at which a computer can be considered, from the highest level, where the user is running programs, or using the computer, to the lowest level, consisting of transistors and wires. Between the high and low levels are a number of intermediate levels. Before we discuss those levels we will present a brief history of computing in order to gain a perspective on how it all came about.

Computer organization refers to the operational unit and their interconnections which are not visible to the programmer and that realize the architectural specifications. It is concerned with the way the hardware components operate and the way they are connected together to form the computer system. It includes attributes like those hardware details transparent to the programmer, such as control signals, interfaces between the computer and peripherals, and the memory technology used.

Still today, the distinction between architecture and organization has been an important one. Many computer manufacturers offer a family of computer models all with the same architecture but with different organization. Architecture may survive many years, but its organization changes with technology.

Computer architecture and design is the combination of study of architecture of computer and the hardware design of the computer. Once the computer specifications are formulated, it is the task of the designer to develop hardware for the system. Computer design is concerned with the determination of what hardware should be used and how the parts should be connected. Early computer design consist of only instruction set design but today many aspects like pipelining, parallel processing should be considered while designing the processor.

Many computer manufacturers offer a family of computer models, all with the same architecture but differences in organization. Consequently, the different models in the family have different price and performance characteristics. A particular architecture may span many years be able to encompass a number of different computer models, its organization changing with changing technology. Due to this, the customer with modest requirements could buy a cheaper, slower model and, if demand increased, later upgrade to a more expensive, faster model without having to abandon software that had already been developed. Hence the customer’s software investment is protected.

In microcomputers, the relationship between architecture and organization is very close.

Change in technology not only influence organization but also result in the introduction of more powerful and more complex architectures. Generally, there is less of a requirement for generation-to-generation compatibility for these smaller machines. Thus, there is more interplay between organization and architecture design decisions.

Why Study Computer Architecture? (Objective)

1. To acquire some understanding and appreciation of a computer system’s functionalcomponents, their characteristics, their performance and their interactions.
2. To understand computer architecture in order to structure a program so that it runs more efficiently on a real machine.
3. To be able to understand the trade off among various components, such as CPU clock speed vs. memory size.
4. To understand the way in which the computer provides architectural support for programming languages and operating systems.