ORGANIZATION AND ARCHITECTURE:
In computer engineering and computer science, computer architecture is a set of rules
and methods that describe the functionality, organization and implementation of
computer systems.
Computer Architecture refers to those attributes of a system that have a direct impact on
the logical execution of a program.
Computer architecture is the conceptual design and fundamental operational
structure of a computer system. It is a blueprint and functional description of
requirements and design implementations for the various parts of a computer,
focusing largely on the way by which the central processing unit (CPU) performs
internally and accesses addresses in memory. It may also be defined as the science
and art of selecting and interconnecting hardware components to create computers
that meet functional, performance and cost goals.
Attributes of Computer architecture:
1. The instruction set
2. The number of bits used to represent various data types (e.g.,
numbers, characters)
3. I/O mechanisms
4. Techniques for addressing memory
Instruction Set Architecture, or ISA, is the image of a computing system that is
seen by a machine language programmer. It includes the instruction set, word size,
memory address modes, processor registers, and address and data formats. OR
The ISA defines the machine code that a processor reads and acts upon as well as
the word size, memory address modes, processor registers, and data formats.
Computer Organization is a lower level and detailed description of the system that
involves how the different parts of the system are interconnected and how they
interoperate in order to implement the ISA. OR
computer organization describes how a particular processor will implement the ISA.
The size of a computer's CPU cache for instance, is an organizational issue that
generally has nothing to do with the ISA.
System Design which includes all of the other hardware components within a
computing system such as:
o Computer buses and switches
o Memory controllers
o Direct Memory Access (DMA)
o Issues like multi-processing
Computer organization:
It refers to the operational units and their interconnections that realize
the architectural specifications. Organizational attributes include those
hardware details transparent to the programmer.
Attributes of Computer organization
1. Control signals
2. Interfaces between the computer and peripherals
3. The memory technology used
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 years and encompass a number
of different computer models, its organization changing with changing
technology. A prominent example of both these phenomena is the
System/370 architecture. This architecture was first introduced in 1970
and included 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 enhancements, 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.
Structure and function of Computer:
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. 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 behaviour 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
Top Down approach to define a system:
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 clearest and most effective.
The computer Top-level structure
