Module 1: introduction to organization and architecture of computer

Organization and architecture

In describing computer system, a distinction is often made between computer architecture and computer organization . Although it is difficult to give precise definition for these terms, a consensus exists about the general areas covered by each.

Computer architecture refers to those attributes of a system visible to a programmer, or put another way, those attributes that have a direct impact on the logical execution of a program.

Computer organization refers to the operational units and their interconnection that realize the architecture specification.

Examples of architecture attributes include the instruction set, the number of bit to represent various data types (e.g.., numbers, and characters), I/O mechanisms, and technique for addressing memory. Organization attributes include those hardware details transparent to the programmer, such as control signals, interfaces between the computer and peripherals, and the memory technology used.

As an example, it is an architectural design issue whether a computer will have a multiply instruction. It is an organizational issue whether that instruction will be implemented by a special multiply unit or by a mechanism that makes repeated use of the add unit of the system. The organization decision may be bases on the anticipated frequency of use of the multiply instruction, the relative speed of the two approaches, and the cost and physical size of a special multiply unit.

Historically, and still today, the distinction between architecture and organization has been an important one. Many computer manufacturers offer a family of computer model, all with the same architecture but with differences in organization. Consequently, the different models in the family have different price and performance characteristics. Furthermore, an architecture may survive many years, but its organization changes with changing technology.

Structure and function

A computer is a complex system; contemporary computers contain million of elementary electronic components. How, then, can one clearly describe them? The key is to recognize the hierarchic nature of most complex system. A hierarchic system is a set of interrelated subsystem, each of the later, in turn, hierarchic in structure until we reach some lowest level of elementary subsystem.

The hierarchic nature of complex systems is essential to both their design and their description. The designer need only deal with a particular level of the system at a time. At each level, the system consists of a set of components and their interrelationships. The behavior at each level depends only on a simplified, abstracted characterization of the system at the nest lower level. At each level, the designer is concerned with structure and function: