Chapter 4: Computer System
4
COMPUTER SYSTEM
Unit Structure
4.0 Objective
4.1 Introduction To Computer Systems
4.2 Computer Types
4.3 Basic Organization of Computer
4.3.1 Input Unit
4.3.2 Memory Unit
4.3.3 Arithmetic and Logic Unit
4.3.4. Output Unit
4.3.5. Control Unit
4.4 Basic Operational Concept
4.5 Bus Structures
4.5.1 Single Bus Structure
4.5.2 Multiple Bus Structures
4.5.3 Bus Design parameters
4.5.3.1 Bus Types
4.5.3.2 Method of Arbitration
4.5.3.3 Bus Timings
4.5.3.4 Bus Width
4.5.3.5 Data Transfer type
4.6 Summary
45
,COMPUTER ORGANIZATION AND ARCHITECTURE
4.0 Objective
Understand the difference between computer architecture and organization.
Describe the different types of computer.
Understand the organization of computer and its various units.
Describe the bus structures in detail and their interconnections.
4.1 Introduction to Computer Systems
The purpose of computer organization and architecture is to prepare clear and
complete understanding of the nature and characteristics of modern-day computer
systems. We begin this text with the overview of computer organization and
architecture and structural /functional view of a computer.
It is necessary to make distinction between computer organization and architecture.
Although it is difficult to give precise definitions for these terms we define them as
follows:
Computer architecture refers to those attributes of a system visible to a
programmer. In other words, we can also say that the computer architecture
refers to the attributes that have a direct impact on the logical execution of
the program.
Computer organization refers to the operational units and their
interconnections that realize the architectural specifications.
The architectural attributes include the instruction set, data types, number of bits
used to represent data types, I/O mechanism, and techniques for addressing
memory. On the other hand, the organizational attributes include those hardware
details transparent to programmer, such as control signals, interfaces between the
computer, memory and I/O peripherals. For example, it is an architectural issue
whether a computer will have a multiply and division instructions. It is an
organizational issue whether to implement multiplication and division by special
unit or by a mechanism that makes repeated use of the add and subtract unit to
perform multiplication and division, respectively. The organizational issue may be
based on which approach to be used depending on the speed of operation, cost and
size of the hardware and the memory required to perform the operation.
Many computer manufactures offer a family of computer models with different
price and performance characteristics. These computers have the same architecture
46
, Chapter 4: Computer System
but different organizations. Their architectures have survived for many years, but
their organizations change with changing technology. For example, IBM has
introduced many new computer models with improved technology to replaced
older models, offering the customer greater speed, lower cost or both. These newer
models have the same architecture with advance computer organizations. The
common architecture between the computer model maintains the software
compatibility between them and hence protects the software investments of the
customers.
In microcomputers, the relationship between computer architecture and
organization is very close. In which, changes in technology not only influence
organization but also result in the introduction of new powerful architecture. The
RISC (Reduced Instruction Set) machine is good example of this.
4.2 Computer Types
A digital computer in its simplest form is a fast electronic calculating machine that
accepts digitized information from the user, processes it according to a sequence of
instructions stored in the internal storage, and provides the processed information
to the user. The sequence of instructions stored in the internal storage is called
computer programand internal storage is called computer memory.
According to size, cost computational power and application computers are
classified as:
Microcomputers
Minicomputers
Desktop computers
Personal computers
Portable notebook computers
Workstations
Mainframes or enterprise system
Serves
Super computers
Microcomputers: As the name implies micro-computers are smaller computers.
They contain only one Central Processing Unit. One distinguishing feature of a
47
4
COMPUTER SYSTEM
Unit Structure
4.0 Objective
4.1 Introduction To Computer Systems
4.2 Computer Types
4.3 Basic Organization of Computer
4.3.1 Input Unit
4.3.2 Memory Unit
4.3.3 Arithmetic and Logic Unit
4.3.4. Output Unit
4.3.5. Control Unit
4.4 Basic Operational Concept
4.5 Bus Structures
4.5.1 Single Bus Structure
4.5.2 Multiple Bus Structures
4.5.3 Bus Design parameters
4.5.3.1 Bus Types
4.5.3.2 Method of Arbitration
4.5.3.3 Bus Timings
4.5.3.4 Bus Width
4.5.3.5 Data Transfer type
4.6 Summary
45
,COMPUTER ORGANIZATION AND ARCHITECTURE
4.0 Objective
Understand the difference between computer architecture and organization.
Describe the different types of computer.
Understand the organization of computer and its various units.
Describe the bus structures in detail and their interconnections.
4.1 Introduction to Computer Systems
The purpose of computer organization and architecture is to prepare clear and
complete understanding of the nature and characteristics of modern-day computer
systems. We begin this text with the overview of computer organization and
architecture and structural /functional view of a computer.
It is necessary to make distinction between computer organization and architecture.
Although it is difficult to give precise definitions for these terms we define them as
follows:
Computer architecture refers to those attributes of a system visible to a
programmer. In other words, we can also say that the computer architecture
refers to the attributes that have a direct impact on the logical execution of
the program.
Computer organization refers to the operational units and their
interconnections that realize the architectural specifications.
The architectural attributes include the instruction set, data types, number of bits
used to represent data types, I/O mechanism, and techniques for addressing
memory. On the other hand, the organizational attributes include those hardware
details transparent to programmer, such as control signals, interfaces between the
computer, memory and I/O peripherals. For example, it is an architectural issue
whether a computer will have a multiply and division instructions. It is an
organizational issue whether to implement multiplication and division by special
unit or by a mechanism that makes repeated use of the add and subtract unit to
perform multiplication and division, respectively. The organizational issue may be
based on which approach to be used depending on the speed of operation, cost and
size of the hardware and the memory required to perform the operation.
Many computer manufactures offer a family of computer models with different
price and performance characteristics. These computers have the same architecture
46
, Chapter 4: Computer System
but different organizations. Their architectures have survived for many years, but
their organizations change with changing technology. For example, IBM has
introduced many new computer models with improved technology to replaced
older models, offering the customer greater speed, lower cost or both. These newer
models have the same architecture with advance computer organizations. The
common architecture between the computer model maintains the software
compatibility between them and hence protects the software investments of the
customers.
In microcomputers, the relationship between computer architecture and
organization is very close. In which, changes in technology not only influence
organization but also result in the introduction of new powerful architecture. The
RISC (Reduced Instruction Set) machine is good example of this.
4.2 Computer Types
A digital computer in its simplest form is a fast electronic calculating machine that
accepts digitized information from the user, processes it according to a sequence of
instructions stored in the internal storage, and provides the processed information
to the user. The sequence of instructions stored in the internal storage is called
computer programand internal storage is called computer memory.
According to size, cost computational power and application computers are
classified as:
Microcomputers
Minicomputers
Desktop computers
Personal computers
Portable notebook computers
Workstations
Mainframes or enterprise system
Serves
Super computers
Microcomputers: As the name implies micro-computers are smaller computers.
They contain only one Central Processing Unit. One distinguishing feature of a
47
