Basic Components of a digital Computer lecture

Chapter – 1
Basic Components of a digital Computer
1.1 Introduction
Recent Advanced research by microelectronics research society, Computer is an
essential part of our society. Each day of our lives are start with digital alarm clock or
mobile, drive car or any other vehicle in digital processor controlled automobiles and
speedometers .work in extensively automated offices. in market all prices are tagged
with a digital system which can store the product information and price of the
product. Computer is used in every productive and non productive field. A great
majority of the computers of our daily use are known as general purpose machines,
other are special purpose machines is an important for solve a specific task, i.e.
scientist use machine for reducing the complexity of their research work.
Computer is a combination of electronics and mechanical, so it is an electro
mechanical device. The technological revolution witnessed in the computer industry
is the result of a long chain of enormous and successful efforts made by two major
forces. These are the academia, and the industry, represented by computer companies.
This chapter describing the architecture of general purpose digital computer system.
1.2 Computer System Architecture
Basic function of computer is process data input by user and output or store the
result of the processed data, for better used in specific application, so computer
architecture is divided in four part input, output control and storage.
For example, controlling the room temperature system sensor sense the current
room temperature, this is input of the system. Control temperature is output of system
and if the temperature is set at 18 degree centigrade for lowest, system sensor control
the compressor and turn off the compressor when room temperature is 18, it is the
control part of system.
The computer revolution continues. Each time the cost of computing improves by
another factor of 10, the opportunities for computers multiply. Applications that were
economically infeasible suddenly become practical. In the recent past, the following
applications were "computer science fiction."
• Automatic teller machines: A computer placed in the wall of banks to distribute
and collect cash would have been a ridiculous concept in the 1950s, when the
cheapest computer cost at least $500,000 and was the size of a car.
• Computers in automobiles: Until microprocessors improved dramatically in price
and performance in the early 1980s, computer control of cars was ludicrous. Today,

computers reduce pollution and improve fuel efficiency via engine controls and
increase safety through the prevention of dangerous skids and through the inflation of
air bags to protect occupants in a crash.
• Laptop computers: Who would have dreamed that advances in computer systems
would lead to laptop computers, allowing students to bring computers to coffeehouses
and on airplanes?
• Human genome project: The cost of computer equipment to map and analyze
human DNA sequences is hundreds of millions of dollars. It’s unlikely that anyone
would have considered this project had the computer costs been 10 to 100 times
higher, as they would have been 10 to 20 years ago.
• World Wide Web: Not in existence at the time of the first edition of this book, the
World Wide Web has transformed our society. Among its uses are distributing news,
sending flowers, buying from online catalogues, taking electronic tours to help pick
vacation spots, finding others who share your esoteric interests, and even more
mundane topics like finding the lecture notes of the authors of your textbooks.
General purpose computer is a supplementary combination of Hardware and
Software. There are two basic components of computer system architecture
(A) Computer Hardware.
(B) Computer Software.
A. Computer Hardware
All above application of computers are use special purpose computer hardware,
which contains less hardware components, General purpose computer containing a
four basic hardware blocks which are memory unit (MU), arithmetic and logic unit
(ALU), input/output unit (IOU), and control unit (CU). Input/output (I/O) devices
input and output data into and out of the memory unit. In some systems, I/O devices
send and receive data into and from the ALU rather than the MU. Programs reside in
the memory unit. The ALU processes the data taken from the memory unit (or the
ALU) and stores the processed data back in the memory unit (or the ALU). The
control unit coordinates the activities of the other three units. It retrieves instructions
from programs resident in the MU, decodes these instructions, and directs the ALU to
perform corresponding processing steps. It also oversees I/O operations.

1. I/O Unit: The input unit contains the hardware devices those are used to enter the
data in to computer system, Keyboard and mouse are most common devices. The
out put contain the hardware devices those are use to output the data from the
computer system, Monitor and printer are most common output devices.
Nowadays so many other I/O devices are shown in Fig 1.2.
2. Control Unit: The control unit maintains the sequence of the operation,
controlling the actions of all other units it can perform the instruction which
constitute the program and direct as per the operation perform by machine.
3. Arithmetic and logic Unit: The ALU unit functions are perform arithmetical
operation, i.e. addition, subtraction, multiplication, division as well as logical
operation i.e. and, or, not.

The control unit gives the instruction to the ALU which operations they have
to perform and where it supplied (store purpose), it is directed to perform the
operations.
4. Memory Unit: The memory unit or storage section of the computer consist the
devices used to store the data or information during the process. Memory unit is
used to hold intermediate and final result of computer program. There are various
types of memory which are used in computer system are as below. In this memory
structure importance of the memory as per top to down approach in Fig 1.3.
B. Computer Software:
If a machine is to be capable of solving a wide range of problems, it must be
able to execute programs written in different high level languages, like ‘C’ or ‘C++’,
while a the only physical components we have to work with are wires and gates.
There is a difficult gap between these physical components and high level languages.
For a system to be practical, the semantic gap must be invisible to most of the users of
the system.
As per the practical rules that if the problem is large then it should be break it
down and use “divide and conquer” thoughts. In programming approach, we divide a
problem into modules and then design each module separately. Each module performs
a specific task and modules need only know how to interface with other modules to
make use of them.
Computer system organization can be approached in hierarchy of levels, in
which each level has a specific function and exists as a distinct hypothetical machine.
By studying computer organization, these layers are implemented and interface with
each other.

Level 6, User Level: is composed of applications and is the level with which everyone
is most familiar. At this level, we run programs such as word processors, graphics
packages, or games. The lower levels are nearly invisible from the User Level.
Level 5, the High-Level Language: Programming languages such as C, C++,
FORTRAN, Lisp, Pascal, and Prolog consisting of this level. These languages must
be translated (using either a compiler or an interpreter) to a language the machine can
understand. Compiled languages are translated into assembly language and then
assembled into machine code. (They are translated to the next lower level.) The user
at this level sees very little of the lower levels. Even though a programmer must know
about data types and the instructions available for those types, she need not know
about how those types are actually implemented.
Level 4, the Assembly Language: As earlier mentioned, compiled higher-level
languages are first converted to assembly, which is directly translated to machine
language. This is a one-to-one translation, meaning that one assembly language
instruction is translated to exactly one machine language instruction. By having
separate levels, we reduce the semantic gap between a high-level language, such as
C++, and the actual machine language (which consists of 0s and 1s).
Level 3, the System Software: deals with operating system instructions. This level is
responsible for multiprogramming, protecting memory, synchronizing processes, and
various other important functions. Often, instructions translated from assembly
language to machine language are passed through this level unmodified.

Level 2, the Instruction Set Architecture (ISA), or Machine Level: consists of the
machine language recognized by the particular architecture of the computer system.
Programs written in a computer’s true machine language on a hardwired computer
(see below) can be executed directly by the electronic circuits without any
interpreters, translators, or compilers.
Level 1, the Control level: control unit makes sure that instructions are decoded and
executed properly and that data is moved where and when it should be. The control
unit interprets the machine instructions passed to it, one at a time, from the level
above, causing the required actions to take place. Control units can be designed in one
of two ways: They can be hardwired or they can be micro programmed.
Level 0, the Digital Logic Level: physical components of the computer system: the
gates and wires. These are the fundamental building blocks, the implementations of
the mathematical logic that are common to all computer systems.
Summary:
Electronics computer are newest but the technology behind the historical
development in the last sixty years, in these chapter we are only concentrated the
architecture of general purpose computer system because of our syllabus but more
architectural study is RISC, and CISC. We will study Memory Organization, ALU,
CPU, and I/O Organization in depth.

Basic Components of a digital Computer lecture

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