1. ORGANIZATION AND ARCHITECTURE
In describing computers, a distinction is often made between computer architecture and computer organization. Although it is difficult to give precise definitions for these terms, a consensus exists about the general areas covered by each (e.g., see [VRAN80], [SIEW82], and [BELL78a]); an interesting alternative view is presented in [REDD76].
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 interconnections that realize the architectural specifications. Examples of architectural attributes include the instruction set, the number of bits used to represent various data types (e.g., numbers, characters), I/O mechanisms, and techniques for addressing memory. Organizational attributes include those hardware details transparent to the programmer, such as control signals; interfaces between the computer and peripherals; and the memory technology used.
For 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 ol the add unit of the system. The organizational decision may be based 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 models, all with the same architecture but with differences in organization Consequently, the different models in the family have different price and performance characteristics. Furthermore, a particular architecture may span many yean and encompass a number of different computer models, its organization changing with changing technology. A prominent example of both these phenomena is the
IBM System/370 architecture. This architecture was first introduced in 1970 and in- cluded a number of models. 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. Over the years, IBM has introduced many new models with improved technology to replace older models, offering the customer greater speed, lower cost, or both. These newer models retained the same architecture so that the customer’s software investment was protected. Remarkably, the System/370 architecture, with a few enhance ments, has survived to this day as the architecture of IBM's mainframe product line.
In a class of computers called microcomputers, the relationship between architecture and organization is very close. Changes 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 organizational and architectural design decisions. An intriguing example of this is the reduced instruction set computer (RISC), which we examine in Chapter 13.
This book examines both computer organization and computer architecture. The emphasis is perhaps more on the side of organization. However, because a computer organization must be designed to implement a particular architectural specification, a thorough treatment of organization requires a detailed examination of architecture as well.
STRUCTURE AND FUNCTION
A computer is a complex system; contemporary computers contain millions of elementary electronic components. How, then, can one clearly describe them? The key is to recognize the hierarchical nature of most complex systems, including the computer [SIM096]. A hierarchical system is a set of interrelated subsystems, each of the latter, in turn, hierarchical in structure until we reach some lowest level of elementary subsystem.
The hierarchical 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 next lower level. At each level, the designer is concerned with structure and function:
Structure: The way in which the components are interrelated
Function: The operation of each individual component as part of the structure
In terms of description, we have two choices: starting at the bottom and building up to a complete description, or beginning with a top view and decomposing the system into its subparts. Evidence from a number of fields suggests that the top- down approach is the dearest and most effective [WEIN75].
The approach taken in this book follows from this viewpoint. The computer system will be described from the top down. We begin with the major components of a computer, describing their structure and function, and proceed to successively lower layers of the hierarchy. The remainder of this section provides a very brief overview of this plan of attack.
Function
Both the structure and functioning of a computer are, in essence, simple. Figure 1.1 depicts the basic functions that a computer can perform. In general terms, there are only four;
Data processing
Data storage
Data movement
Control
The computer, of course, must be able to process data. The data may take a wide variety of forms, and the range of processing requirements is broad. However, we shall see that there are only a few fundamental methods or types of data processing
It is also essential that a computer store data. Even if the computer is processing data on the fly (Le„ data come in and get processed, and the results go out immediately), the computer must temporarily store at least those pieces of data that are being
In describing computers, a distinction is often made between computer architecture and computer organization. Although it is difficult to give precise definitions for these terms, a consensus exists about the general areas covered by each (e.g., see [VRAN80], [SIEW82], and [BELL78a]); an interesting alternative view is presented in [REDD76].
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 interconnections that realize the architectural specifications. Examples of architectural attributes include the instruction set, the number of bits used to represent various data types (e.g., numbers, characters), I/O mechanisms, and techniques for addressing memory. Organizational attributes include those hardware details transparent to the programmer, such as control signals; interfaces between the computer and peripherals; and the memory technology used.
For 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 ol the add unit of the system. The organizational decision may be based 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 models, all with the same architecture but with differences in organization Consequently, the different models in the family have different price and performance characteristics. Furthermore, a particular architecture may span many yean and encompass a number of different computer models, its organization changing with changing technology. A prominent example of both these phenomena is the
IBM System/370 architecture. This architecture was first introduced in 1970 and in- cluded a number of models. 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. Over the years, IBM has introduced many new models with improved technology to replace older models, offering the customer greater speed, lower cost, or both. These newer models retained the same architecture so that the customer’s software investment was protected. Remarkably, the System/370 architecture, with a few enhance ments, has survived to this day as the architecture of IBM's mainframe product line.
In a class of computers called microcomputers, the relationship between architecture and organization is very close. Changes 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 organizational and architectural design decisions. An intriguing example of this is the reduced instruction set computer (RISC), which we examine in Chapter 13.
This book examines both computer organization and computer architecture. The emphasis is perhaps more on the side of organization. However, because a computer organization must be designed to implement a particular architectural specification, a thorough treatment of organization requires a detailed examination of architecture as well.
STRUCTURE AND FUNCTION
A computer is a complex system; contemporary computers contain millions of elementary electronic components. How, then, can one clearly describe them? The key is to recognize the hierarchical nature of most complex systems, including the computer [SIM096]. A hierarchical system is a set of interrelated subsystems, each of the latter, in turn, hierarchical in structure until we reach some lowest level of elementary subsystem.
The hierarchical 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 next lower level. At each level, the designer is concerned with structure and function:
Structure: The way in which the components are interrelated
Function: The operation of each individual component as part of the structure
In terms of description, we have two choices: starting at the bottom and building up to a complete description, or beginning with a top view and decomposing the system into its subparts. Evidence from a number of fields suggests that the top- down approach is the dearest and most effective [WEIN75].
The approach taken in this book follows from this viewpoint. The computer system will be described from the top down. We begin with the major components of a computer, describing their structure and function, and proceed to successively lower layers of the hierarchy. The remainder of this section provides a very brief overview of this plan of attack.
Function
Both the structure and functioning of a computer are, in essence, simple. Figure 1.1 depicts the basic functions that a computer can perform. In general terms, there are only four;
Data processing
Data storage
Data movement
Control
The computer, of course, must be able to process data. The data may take a wide variety of forms, and the range of processing requirements is broad. However, we shall see that there are only a few fundamental methods or types of data processing
It is also essential that a computer store data. Even if the computer is processing data on the fly (Le„ data come in and get processed, and the results go out immediately), the computer must temporarily store at least those pieces of data that are being
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Abbe bsdk book se sara copy paste krke yha chapawa he chodu kuch apna to likh leta
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