Welcome
to Computer Education for All, this video tutorial covers a Complete Tutorialon Computer Systems for Class 9th Federal Board Computer Science Subject Unit No. 1
A
computer system is a fundamental part of modern life. It has revolutionized the
way we work, communicate, learn, and entertain ourselves. A computer system is
not just a single device but a sophisticated combination of hardware and
software components that work together to process information, solve problems, and
execute a multitude of tasks.
Understanding
computer systems is very important in today's digital age, whether some one is
a casual user or a professional in the field of computing. It empowers the
users to utilize the capacities of computers for diverse purposes, from
business and scientific research to creative activities and entertainment.
1.1
Brief History of Computer Systems and Generation
Computers
A
computer is a programmable electronic device that performs arithmetic and
logical operations automatically using a set of instructions provided by the
user. When we study the aspects of computing and computers, it is important to
know about the history of computers.
1.1.1
Early Computing Devices
Humans
used sticks, leaves, stones, and bones as counting tools before computers were
invented. More computing devices were produced as technology advanced and human
intelligence improved over time. A few early-age computing devices are
discussed as follows.
Abacus
The
abacus was one earliest counting devices, consisting of beads or stones on rods
or wires. It has been used for centuries in various cultures for arithmetic
calculations by sliding beads to represent different numerical values. The
abacus is shown in Fig. 1.1.
Fig. 1.1 Abacus
Napier's
Bone
John
Napier developed Napier's bones, a manually operated calculating device. It
used 9 separate strips (bones) marked with numerals to multiply and divide. It
was also the first machine to calculate using the decimal point system.
Napier's Bone is shown in Fig. 1.2.
Fig.1.2
Napier's Bone
Unit
1
COMPUTER
SYSTEMS
PASCALINE
Pascaline
was invented in 1642 by Bliaise Pascal, a French mathematician. It was thought
to be the first mechanical and automated calculator. It consisted of a wooden
box with gears and wheels in it. Pascaline is shown in Fig. 1.3.
Fig. 1.3
Pascaline
STEPPED RECKONER OR LEIBNIZ WHEEL
In
1673, a German mathematician named Wilhelm Leibniz improved on Pascal's
invention to create this device. It was a digital mechanical calculator known
as the stepped reckoner because it used grooved wheels instead of gears.
Leibniz wheel is shown in Fig. 1.4.
Fig.1.4 Leibniz
wheel
Difference Engine
In
the early 1820s, Charles Babbage created the Difference Engine. It was a
mechanical computer that could do basic computations. It was a steam-powered
calculating machine used to solve numerical problems.
Analytical Engine
Charles
Babbage created another calculating machine, the Analytical Engine, in 1830. It
was a mechanical computer that took input from punch cards. It was capable of
solving any mathematical problem and storing data in memory. Analytical Engine
is shown in Fig. 1.5.
Fig.1.5
Analytical Engine
Tabulating Machine
An
American Statistician - Herman Hollerith invented this machine in the year
1890. Tabulating Machine was a punch card-based mechanical calculator. It could
compute statistics and record data or information. Hollerith began
manufacturing these machines in his company, which ultimately became International
Business Machines (IBM) in 1924. Tabulating machine is shown in Fig. 1.6.
Fig. 1.6
Tabulating Machine
Differential Analyzer
Vannevar
Bush introduced the first electrical computer, the Differential Analyzer, in
1930. This machine was made up of vacuum tubes used as switches to electrically
impulse to do calculations. It was capable of performing 25 calculations per
minute. Differential Analyzer is shown in Fig. 1.7.
Fig. 1.7
Differential Analyzer
Mark I
The
next successful computing machine invented was a digital computer known as
Mark-I. It was invented by Howard Aiken in 1944. Mark-I could add three numbers
having eight digits in one second. It could print out its results on punched
cards or on an electric typewriter. Mark-I was 50 feet long, 8 feet high and
weighed about 5 tons. It used 3,000 electric switches. Mark-I is shown in Fig.
1.8.
Fig.1.8 Mark-I
Computer
1.1.2 Computer Generations
History
of computers is a chain that runs from the ancient abacus and the analytical
engine of the nineteenth century, through the modern quantum computers of
present age. It is generally divided into five generations. Each generation of
computers is characterized by major technological developments of that time.
First Generation Computers (1940-1956)
First-generation
computers, emerged in the late 1940s and lasted through the early 1950s, were
characterized by the use of vacuum tube technology. Vacuum tubes were used as a
main electronic devices in the first generation computers. It consists of a
glass tube containing electrodes (cathode, anode, and some additional elements)
and a partial vacuum. A vacuum tube is shown is Fig. 1-9.
Fig.1.9 Vacuum
Tube
The
following are some characteristics of first-generation computers.
·
Vacuum tubes were used in
first-generation computers.
·
The processing speed was slow.
·
Memory capacity was limited.
·
These computers were massive,
occupying entire rooms.
·
First-generation computers were both
costly and unreliable.
·
They consumed significant power and
generated substantial heat. Input relied on punched cards.
·
Output was obtained through
printouts via electric typewriters.
·
Machine language was the only
programming paradigm.
Some
examples of first generation Mini/Mainframe computers are ENIAC, UNIVAC I, IBM
604, Mark-I and EDSAC.
Second Generation Computers (1956-1963)
Second
Generation computers emerged in the late 1950s and extended through the early
1960s. This period marked a significant advancement in computing technology,
characterized by the transition from vacuum tubes to transistors. Transistor
functions like a vacuum tube. It was faster, more reliable, smaller and much
cheaper than vacuum tube. A transistor is shown in Fig 1-10.
Fig. 1.10
Transistor
The
following are some characteristics of second-generation computers.
·
Second generation computers replaced
vacuum tubes with transistors, leading to enhanced efficiency.
·
The adoption of transistors resulted
in a reduction in computer by improvements in speed and memory capacity.
·
Second-generation computers
demonstrated increased reliability and cost- effectiveness.
·
Key input and output methods
included punch card readers, magnetic tapes, magnetic disks, and printers.
·
Assembly language was employed for
programming purposes.
·
This generation introduced
high-level programming languages such as FORTRAN and COBOL.
·
Some examples of second-generation
computers comprise UNIVAC II, IBM 7030, General Electric GE 635, and Control
Data Corporation's CDC 1604 computers.
Third Generation Computers (1963 - 1971)
Third-generation
computers emerged in the 1960s and extended into the 1970s. This era marked
further advancements in computing technology, characterized by the use of
integrated circuits (ICs) and the development of smaller, faster, and more
reliable systems. IC chips are shown in Fig.1-11.
Fig.1.11 IC
Chips
The
following are the characteristics of third generation of computers.
·
Third-generation computers used
Integrated Circuit (IC) chips.
·
The utilization of IC chips led to
enhancements in computer speed and memory.
·
These computers demonstrated
improvements in energy efficiency, size reduction, cost- effectiveness, and
reliability compared to second- generation computers.
·
Interaction with third-generation
computers involved the use of a keyboard and monitor.
·
These computers had the capability
to concurrently run multiple application programs.
DO
YOU KNOW?
Intel
invented the world's first microprocessor, the Intel 4004 in November, 1971
Examples
of third-generation computers include IBM System/360 and Control Data
Corporation's 3300 and 6600 computers.
Fourth Generation Computers (1971-Present)
Fourth-generation
computers, starting from late 70s to the present, are characterized by
significant advancements in technology, particularly the development of Large
Scale Integration (LSI) and Very Large Scale Integration (VLSI) chips. One of
the key innovations of this era was the development of the microprocessor, a
single chip capable of handling all processing tasks within a computer. A
microprocessor is shown in Fig. 1-12.
Fig.1.12
Microprocessor
The
following are the characteristics of fourth generation of computers.
·
The introduction of microprocessors
marked a defining feature of fourth-generation computers, leading to the
emergence of microcomputers.
·
Fourth-generation computers are
known for exceptional speed, large storage capacity, and the incorporation of
advanced input/output devices.
·
Microcomputers in this generation
are characterized by their small size, high reliability, low power consumption,
and affordability.
·
A wide variety of software became
available for use in microcomputers during the fourth generation.
·
Operating systems with Graphical
User Interfaces (GUIS) were developed during this period, enhancing user
interaction and experience.
·
Fourth-generation computers support
multimedia software, enabling the integration of text, image, sound, and video.
·
These computers are compatible with
modern programming languages such as Visual Basic, C++, Java, and Python,
facilitating the development of powerful software applications.
·
Fourth-generation computers support
a diverse range of portable and wireless input/output devices.
Examples of
microprocessors developed during this era include the Intel Pentium series,
Dual Core, Core2 Duo, Core i3, i5, 17, and AMD Athlon. Notable fourth-generation
computer models include the IBM ThinkPad series, HP Pavilion series, Dell
Inspiron series, as well as Apple's MacBook Pro and MacBook Air series.
Fifth Generation Computers (Present to Beyond)
The timeline
for the fifth generation is not as precisely defined as the earlier
generations, but it is generally associated with ongoing advancements in
computing that were expected to emerge in the late 20th century and beyond. The
main objective of fifth generation of computers is to develop devices that can
understand natural languages and have thinking power. This is a big challenge
for computer developers and programmers to design such systems and software for
them.
The following
are the characteristics of fifth generation of computers.
·
The primary focus of
fifth-generation computers tis to develop and utilize Al (Artificial
Intelligence) technologies. This involves machines (called Robots) with the
capability to learn, think, innovate, reason, and solve problems automatically
and independently.
·
Fifth-generation computers support
advanced parallel processing capabilities, allowing them to execute multiple
tasks simultaneously and handle complex computations more efficiently.
·
A key aspect of fifth-generation
computing is the ability to understand and respond to human languages. This
involves developing systems capable of NLP (Natural language processing) and
communication.
·
These computers are planned to
incorporate advanced ES (Expert systems), which are software programs designed
to replicate the decision-making abilities of human experts in specific fields,
like medical, mining, and engineering.
·
In this generation of computers user
interfaces have become more intuitive and user-friendly, incorporating features
like Voice recognition and gesture-based controls.
1.2
Understanding Systems and their Types
What is a
System?
A
"System" refers to a collection of interconnected or interrelated
components or elements that work together to achieve a specific purpose or
function. Systems can be found in various aspects of life, from natural
ecosystems to human-made artificial systems. Any kind of system is a group of
resources which work collectively in order to produce desired results from
given inputs. It accepts input and produces the output.
Understanding
and categorizing systems is important for various fields, including
engineering, biology, sociology, and management, as it allows for better
analysis, design, and optimization of these systems to achieve their intended
goals. Different types of systems may show distinct properties and behaviors,
which necessitate different approaches to study and manage them effectively.
1.2.1 Natural
and Artificial Systems
Natural Systems
A natural
system is an interconnected collection of elements or components that exist in
the nature. These systems are typically found in the environment and are
characterized by their ability to self-regulate, adapt, and maintain a certain
degree of stability. Natural systems are incredibly diverse and fascinating,
each with its unique characteristics and interactions. Some natural systems are
shown in Fig. 1.13.
Fig.1.13
Natural Systems
The following
are a few examples of natural systems.
Ecosystems: Ecosystems are
perhaps the most common and diverse natural systems. They encompass various
types, including:
Forest
Ecosystems: Such as a tropical rainforest with its myriad of plant and animal
species.
Aquatic
Ecosystems: Like freshwater lakes, rivers, and marine ecosystems such as coral
reefs.
Grassland
Ecosystems: Such as the African savanna, home to grazing animals like zebras
and wildebeests.
Weather
Systems:
Weather systems involve the interactions of the Earth's atmosphere, including
phenomena like rainfall, wind patterns, and temperature changes.
Geological
Systems:
These systems encompass geological processes and features like:
Plate
Tectonics: movement of
Earth's lithospheric plates, leading to phenomena like earthquakes and volcanic
eruptions.
Mountain
Systems: Such as the Himalayas, formed by tectonic
plate collision. Hydrological Systems: These systems involve the movement,
distribution, and quality of water on Earth, including rivers, lakes, and the
water cycle.
Solar System: Our solar
system itself is a natural system, with the Sun, planets, moons, asteroids, and
comets all interacting under the influence of gravity.
Biological
Systems:
Biological systems encompass a wide range of living organisms and their
interactions:
Human Body: A complex
biological system with organs, tissues, cells, and biochemical processes.
Coral Reef: An ecosystem
built by coral colonies and inhabited by various marine species.
Rainforest
Canopy: The
upper layer of a rainforest, home to a unique set of plants and animals.
Artificial
Systems
Artificial systems, also known as
man-made or human-made systems, are created and designed by humans to serve
specific purposes, solve problems, or achieve particular goals. Unlike natural
systems, which occur organically in the natural world, artificial systems are
intentionally constructed by humans to address various needs and objectives.
These systems can range from simple devices to highly complex structures, and
they exist in numerous domains.
Artificial systems are essential
components of modern society, contributing to our ability to meet a wide range
of needs and advance in various fields. They often require careful planning,
engineering, and maintenance to function efficiently and effectively. Some
artificial systems are shown in Fig. 1.14.
Fig. 1.14 Artificial Systems
The following are some common
examples of artificial systems.
Communication
Systems:
Telephone
Networks: Created to facilitate voice communication over long distances.
Internet and
Computer Networks: Built to enable data sharing and digital communication globally.
Satellite
Communication Systems: Developed for long-distance, wireless communication.
Information
Systems:
Databases: Used for
storing and retrieving data efficiently.
Software Applications: Such as word
processors, spreadsheets, and video editing software.
Transportation
Systems:
Automobiles: Designed for
personal and mass transportation on roads.
Aircraft: Engineered for
air travel, including commercial airplanes, helicopters, and drones.
Trains and Rail
Systems:
Developed for efficient land transportation on tracks.
Subways and
Mass Transit: Designed to move large numbers of people within urban areas.
Energy Systems:
Power Plants: Designed to generate electricity using various energy sources like
coal, natural gas, nuclear, or renewable resources.
Renewable Energy Systems: Including solar panels, wind turbines, and hydroelectric plants.
Electrical Grids: Infrastructure for the distribution of electrical power.
Manufacturing
Systems:
Factory Automation: Systems that automate manufacturing processes, such as robotics
and conveyor systems.
Assembly Lines: Organized systems for mass-producing goods.
Healthcare
Systems:
Hospital Information Systems (HIS): Designed to
billing, and other healthcare data.
Medical Devices: Including MRI machines, X-ray equipments and artificial organs.
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Welcome
to Computer Education for All, Today’s Topic;;
1.3 Core Components of a Computer System
A
computer system comprises of several core components that work together to
perform various tasks. The essential components of a computer system include
Input devices, Output devices, System unit (motherboard, memory, CPU, power
supply, etc.), and data storage devices.
1.3.1 Input
Devices
Input devices
are used to provide data into the computer system. Input devices allow us to
communicate with the computer. Some commonly used input devices are keyboard,
mouse, microphone, scanner, barcode reader, digital camera and touch screens.
Keyboard
It is the main
input device to communicate with the computer. It allows the computer user to
enter letters, numbers and special symbols into the computer. A keyboard is
shown is Fig.1.15.
POINT TO
PONDER:
Why the keys on
keyboard are not arranged in alphabetical order?
Mouse
It is a
hand-held device used to control the movement of cursor or pointer on the
screen. It has two or three buttons at the front that allows the computer user
to make selection in menu, draw graphics or open files, folders and programs. A
typical mouse is shown is Fig.1.16.
Microphone
It is a device
that allows computer user to input audio into the computer. It changes audio
signals into electrical signals which are translated into digital form by the
sound card for processing in the computer. A microphone is shown in Fig. 1.17.
Scanner
It is a device
that captures images from photographs, magazines, books etc. and stores them in
computer in digital form. These images can be edited, displayed on the screen
or inserted in documents. A scanner is shown in Fig.1.18.
Barcode Reader
It is a device
that reads the barcode printed on products that represents product code,
description and price. This information is used by the computer to print bill
for the customer. A barcode reader is shown in Fig.1.19.
Digital Camera
It is
input/output device used to capture pictures and store them in digital form.
These pictures can be downloaded to computer for editing, viewing or inserting
in documents. A digital camera is shown in Fig. 1.20.
Touch Screen
It is a
pressure-sensitive display screen that is used to interact with the computer by
touching pictures or words with finger. Touch screen is more commonly used with
mobile phone and tablet. A touch screen is shown in Fig. 1.21.
1.3.2 System
Unit
System unit is
the main part of computer. It includes motherboard, power supply and drives
(such as DVD and hard disk) inside the computer casing. All the input/output
devices of a computer are connected to system unit through the ports.
Motherboard
Motherboard is
the main circuit board inside the system unit. It contains microprocessor, main
memory, expansion cards, many IC chips, connectors, and other electronic
components. It has many buses (electric pathways) printed on it. These are used
to transmit information between various components of the computer. All the
input/output devices are connected to the motherboard. A motherboard is shown
in Fig.1.22.
Microprocessor
A
microprocessor is the main chip on the motherboard that controls all the
activities of the computer. It is also known as Central Processing Unit (CPU)
or simply processor. It contains Control Unit (CU), Arithmetic Logic Unit (ALU)
and registers. A microprocessor and the block diagram of CPU are shown in Fig.
1.23.
ALU is the part
of the computer that performs all the calculations and comparisons. It consists
of arithmetic unit and logic unit. Arithmetic unit performs all the arithmetic
operations such as addition, subtraction, multiplication, and division. Logic
unit performs logical operations which include comparisons of numbers or
alphabets.
Control unit
controls the operations of all the components of the computer. It controls the
working of all the input/output devices, storage devices and ALU. CU loads
programs into memory and executes them. It consists of very complicated
circuits.
Registers are
small memory units inside the microprocessor used to temporarily store some
information during the execution of a program. Some commonly used registers are
Instruction Register, Accumulator Register, Data Register and Memory Address
Register.
1.3.3 Storage
Devices
Storage devices
are used to store programs and data that are not currently used by the
computer. They have huge storage capacity. Therefore, they are also known as
mass storage devices or secondary memory. Hard disk is the most commonly used
storage device that is fixed inside the system unit. Portable storage devices
are CD, DVD, memory cards and USB flash drive. Portable storage devices have
less storage capacity than hard disk but they are cheap and easy to carry.
Hard Disk
A hard disk is
a magnetic storage device used to store computer data permanently. It has
storage capacity of hundreds of Gigabyte (GB). It is fixed inside the computer
casing. Portable hard disk is also available that is attached to USB port.
Compact Disk
(CD)
CD (DVD) is a
portable optical storage device with a storage capacity of 700 Megabytes (MB).
A CD is 1.2 millimeter thick with a diameter if 120 millimeters. CD drive is
used to read data from or write data to a CD.
Digital
Versatile Disk
DVD is also
portable optical storage device. It has the same thickness and diameter as CD
but has more storage capacity. Its storage capacity is in the range of 4 to 16
GB. A DVD writer is installed in the computer to read data from or write data
to a DVD. A CD can also be used in a DVD writer.
Memory Card
Memory card is
a small storage device having storage capacity of few Gigabytes. It is
available in different sizes and storage capacities. Memory cards are generally
used in laptop computers and portable devices such as mobile phone and digital
camera for storing pictures, audio and video. A memory card is Fig.1.24 Memory
Card shown in Fig.1.24.
USB Flash Drive
USB flash drive
is a small portable drive that is connected to computer through USB port. It is
also known as USB memory. It is very fast in operation and its storage capacity
is up to 128 GB till now. A USB flash drive is shown in Fig.1.25.
1.3.4 Output
Devices
Output devices
are used to display text, graphics, and images on the monitor or to print
information on paper. Information displayed on monitor is known as softcopy and
anything printed on paper is known as hardcopy or printout. Commonly used
output devices are monitor, printer, plotter and speaker.
Monitor
It is an output
device that has a screen on which information is displayed. It has two common
types i.e. CRT (Cathode Ray Tube) monitor and LED (Light Emitting Diode)
monitor. CRT monitor is very similar to old television. It is almost obsolete
due to its big size and low display quality. LED monitor is slim, uses less
power and has better display quality than CRT monitor. CRT and LED monitors are
shown in Fig. 1-26.
Printer
Printer is an
output device that prints text and graphics on paper which is known as
hardcopy. There are two types of printers which are impact and non-impact
printers.
Impact printer
Impact printer
uses electro-mechanical mechanism which causes the character shape to strike
against the paper and leave an image of the character on the paper. Dot matrix
printer is the most commonly used impact printer. The printing speed varies
from 50 to 500 cps (characters per second). Their printing is very cheap but
print quality is poor. They produce lot of noise while printing. These printers
are still in use for p r printing invoices, bank statements, utility bills,
etc. A Dot matrix printer is shown in Fig. 1-27(a).
FOR YOUR
INFORMATION: The first high-speed printer was developed in 1953 by Remington
Rand (an early American business machines manufacturer) for use on UNIVAC
computer.
Non-Impact
printer
Non-Impact
printer prints without striking the paper. There are two types of non- Impact
printers which are inkjet and laser printers. Inkjet printer stores ink in
cartridge and sprays on paper through fine nozzles on the print-head. Laser printers
use technology similar to photocopying machine. Laser printer is more
expensive, faster and has very high print quality compared to inkjet printer.
Inkjet printers are used in all sectors such as homes and simple businesses.
Laser printers are perfect for large scale businesses. Inkjet and laser
printers are shown in Fig.1.27.(b,c).
Plotter
Plotter is an
output device used for printing engineering drawings, machine parts, building
designs, maps, charts and panna-flexes etc. on large size papers/sheets. Such
large size printing is not possible on printers. It is more expensive than
printer. There are two types of plotters, that is, ink plotter and pen plotter.
Ink plotter is used for printing images whereas pen plotter is used for
printing engineering drawings, machine parts, building designs, etc. Plotter is
a slow output device but its printing quality is good. A plotter is shown in
Fig. 1.28.
Speaker
Speaker is a
device used to produce audio output. A pair of speakers are attached to the
sound card on the motherboard. Speakers are commonly used with multimedia
software and for playing music and videos on computer. A pair of speakers are
shown in Fig.1.29.
1.3.5 Ports,
Expansion Slots and Expansion Cards Ports
Port is an
interface for connecting various devices to the system unit. These are located
on the motherboard and are usually seen at the back of the system unit. There
are various types of ports for connecting keyboard, mouse, monitor, microphone,
speakers.
and
other input/output devices as shown in Fig.1.30. (a). In modern computers, USB
(Universal Serial Bus), HDMI (High-Definition Multimedia Interface), DVI
(Digital Visual Interface), Audio and LAN (Local Area Network) ports are used
for connecting various devices to the computer. These devices include digital
camera, scanner, printer, external hard disk or DVD writer and USB memory, etc.
Expansion Slots
and Expansion Cards
Expansion slots
are long narrow sockets on the motherboard used for installing expansion cards.
Expansion cards
are small circuit boards. These cards add new capabilities to the computers.
Commonly used expansion cards are sound card, graphics card, modem card and
network card. In modern computers these cards are built-in on the motherboard.
A network card is shown in Fig. 1.31.
1.4 Von Neumann
Architecture
Von Neumann
Architecture is an essential concept in computer science that explains how a
computer's hardware and software work together to process information. It was
first published by John von Neumann in 1945. His computer architecture design
consists of a Control Unit, Arithmetic and Logic Unit (ALU), Memory Unit,
Registers and Inputs/Outputs.
Von Neumann
architecture is based on the stored-program computer concept, where instruction
data and program data are stored in the same memory. This design is still used
in most computers produced today. Modern Von Neumann architecture is shown in
Fig. 1.32.
Fig. 1.32 Von Neumann
architecture
Central
Processing Unit (CPU)
The Central
Processing Unit (CPU) is the main electronic circuit responsible for executing
the instructions of a computer program. The CPU contains the ALU, CU and a
variety of registers.
Registers
Registers are
high speed storage areas in the CPU. All data must be stored in a register
before it can be processed.
|
MAR |
Memory Address Register |
Holds the memory location of data that needs to be accessed. |
|
|
|
|
|
MDR |
Memory Data Register |
Holds data that is being transferred to or from memory |
|
AC |
Accumulator |
Where intermediate arithmetic and logic results are stored. |
|
PC |
Program Counter |
Contains the memory address of the next instruction to be
executed. |
|
CIR |
Current Instruction Register |
Contains the current instruction during processing. |
Arithmetic and
Logic Unit (ALU)
The ALU allows
arithmetical (add, subtract etc.) and logical (AND, OR, NOT etc.) operations to
be carried out.
Control Unit
(CU)
The control
unit controls the operation of the computer's ALU, memory and input/output
devices, telling them how to respond to the program instructions interpreted
from the memory unit. The control unit also provides the timing and control
signals required by other computer components. Control Unit is shown in Fig.1.33
Buses
Buses are the
pathways or lines by which data is transmitted from one part of a computer to
another, connecting all major internal components to the CPU and memory. A
standard CPU system bus is comprised of a control bus, data bus and address
bus.
Address Bus Carries the addresses of data (but not the
data) between the processor
Data Bus Carries data between the processor,
the memory unit and the input/output devices
Control Bus Carries control signals or commands from
the CPU in order to control and coordinate all the activities within the
computer.
Memory Unit
In Von Neumann
architecture the memory unit consists of RAM and Cache memory, sometimes
referred to as primary or main memory. This memory is fast and also directly
accessible by the CPU. RAM is split into partitions. Each partition consists of
an address and its contents (both in binary form). The address uniquely
identifies every location in the memory. Memory Unit is shown in Fig.1.34
Input/Output
(1/0) Controller
This component
manages the flow of data between the CPU and external devices like hard drives,
USB devices, and network interfaces.
1.5 Data
Transmission within a computer system
Data
transmission within a computer system involves the movement of data/information
between various components such as the CPU, memory, storage devices, and
input/output devices. This process is vital for the proper functioning of a
computer and its ability to execute tasks efficiently.
The following
point give an overview of how data is transmitted within a computer system:
Bus
Architecture: Computers use a bus architecture to transmit data. A bus is a
communication pathway that allows the transfer of data and control signals
between various components such as the CPU, memory, and peripheral devices. It
is just like a highway system for data inside the computer system. There are
different types of buses:
·
Data Bus: Carries the
actual data being transmitted.
Address Bus: Specifies the
location in memory or I/O device where data should be read from or written to.
Control Bus: Carries
control signals that manage the data transfer process (e.g., read, write, halt,
etc.).
Data Paths: Inside the
CPU, data paths are dedicated paths known as data circuits that facilitate the
movement of data between various functional units. These functional units
include the Arithmetic Logic Unit (ALU), registers, cache, and other components
involved in data processing. The data paths allow the CPU to perform operations
on data by providing routes for data to move within the processor.
Data paths are
more internal and pertain to how data moves within the CPU, while bus
architecture addresses the broader communication infrastructure that enables
data transfer between the CPU and other parts of the computer system. Details
are shown in Fig.1.36
Registers: Registers are
small, high-speed storage units located within the CPU. They hold data that is
frequently used by the CPU during processing. Data is quickly transferred
between registers and main memory via the buses.
Memory
Hierarchy: Modern computers use a memory hierarchy to improve data
transmission. Data is stored in different levels of memory, ranging from
high-speed but small Cache memory to larger and slower RAM, and even slower
secondary storage (hard drives, SSDs). The CPU fetches data from the higher
levels of the hierarchy first due to their faster access times.
Instruction
Cycle:
When a program is executed, it goes through a series of steps called the
instruction cycle. This cycle involves fetching the next instruction from
memory, decoding it to understand what operation is required, fetching operands
from memory or registers, executing the operation, and storing the results back
in memory or registers. It is called fetch-decode-execute cycle.
Pipeline
Processing: Many modern CPUs use pipelining to increase efficiency. In a
pipeline, multiple instructions are in different stages of execution
simultaneously. This allows for better utilization of the CPU's resources and
faster execution of instructions. Interrupts and I/O: Input/output devices
(e.g., keyboard, mouse, display, network interface) communicate with the CPU
using interrupts. An interrupt is a signal that halts the current program's
execution to handle an important event. This allows data to be transmitted
between the CPU and these devices.
Parallelism: Some computer
architectures use parallelism to improve data transmission speed. This can
involve multiple cores within a CPU or even distributed systems with multiple
interconnected computers working together.
1.6 Types and Hierarchy
of Computer Memory
In computing,
memory refers to the physical devices used to store programs (sequence of
instructions) or data on a temporary or permanent basis for use in a computer
or other digital/computing devices. Memory in a digital computer contains the
main part of the operating system and all the application programs and related
data that are being used. Fig. 1.37 shows different types of computer memory.
Fig. 1.37
Memory Classification
1.6.1 Memory
Terminology
The following
are some important memory terms.
Bit: The smallest
unit of memory in digital computer is a bit, which stands for binary digit 0 or
1. The memory of a computer consists of millions of memory (or electronic)
cells. Each cell contains one bit of information. The memory cell has two
states, ON and OFF. The ON state represents a binary 1 and OFF state binary 0.
Byte: Byte is the
basic unit of computer memory and it is the minimum piece of data to be
processed by a computer. A group of 8 bits is known as one byte. One byte of
memory is required to store one character in the computer, for example, 'A',
'a', 'b', "", etc. A byte is generally used to express the memory
size of a computer. Computer memory is measured in terms of bytes. The higher
units are Kilobyte (KB), Megabyte (MB), Gigabyte (GB) and Terabyte (TB). In the
future, memories will also be available in Petabyte (PB) and Exabyte (EB) as
indicated in red color in Table 1.1. The relationship between the memory units
is shown in Table 1.1.
Memory Word: In computing,
the smallest amount or size of data that a computer can process is called a memory
word. It is a fixed-sized piece of data handled as a unit by the processor. The
number of bits in a word is called the word size. Word size in modern computers
typically ranges from 16 to 64 bits, depending on the size of the computer. A
computer that has a bigger word size can transfer more bits into the
microprocessor at a time for processing and this improves the processing speed
of the computer.
|
MEMORY UNIT |
EQUIVALENT TO |
|
1 Bit |
1 Bit |
|
1 Nibble |
4 Bits |
|
1 Byte |
8 Bits |
|
1 Kilobyte |
1024 Bytes |
|
1 Megabyte |
1, 024 Kilobytes |
|
1 Gigabyte |
1, 024 Megabytes |
|
1 Terabyte |
1, 024 Gigabytes |
|
1 Petabyte |
1, 024 Terabytes |
|
1 Exabyte |
1, 024 Petabytes |
|
1 Zettabyte |
1, 024 Exabytes |
|
1 Yottabyte |
1, 024 Zettabytes |
Table 1.1
Memory Units and their Equivalents
Word Size: Word size
refers to the number of bits that a computer's CPU can process or manipulate in
a single instruction or operation. The word size of a CPU is a fundamental
characteristic that affects its performance and capabilities. For example, a
CPU with a 32-bit word size can process data in 32-bit chunks, while a CPU with
a 64-bit word size can process data in 64-bit chunks. A larger word size
generally allows a CPU to handle larger integers, perform more complex
arithmetic operations, and address larger memory spaces.
1.6.2 Memory
Built-up and Retention Power
All types of
computer memory, as far as their built-up or manufacturing is concerned, are
divided into Chip memory, Magnetic memory, and Optical memory. And as far as
their retention power is concerned these memories are divided into Volatile
memory and non-volatile memory.
Chip Memory
A chip is a
small piece of semi-conducting material (usually silicon). A small circuit
called IC (Integrated Circuit) is embedded on it. A typical chip contains
millions of electronic components (transistors).
Chip memories
are better in speed compared to other memory types due to the absence of
mechanical moving parts. Unlike traditional forms of memory, chip memories rely
on electric currents for their operation. This reliance on electrical processes
contributes to their rapid data access and retrieval capabilities.
Examples of
chip memory are main memory (RAM, ROM, and Cache), Flash memory drives, memory
cards, registers, and Solid State drives (SSDs). Many special-purpose chips,
known as application-specific integrated circuits, are also being made today
for automobiles, home appliances, telephones, and other devices. Different
types of chip memory devices are shown in Fig.1.38.
Fig.1.38 Chip
Memory devices
Magnetic Memory
One of the most
widely used types of digital data storage is magnetic memory/storage. This
refers to any type of data storage using a magnetized medium. Magnetic tapes
and disks are examples of magnetic memory devices. A thin layer of magnetic
material is coated on the
DO YOU KNOW?
In September
1956 IBM launched the 305 RAMAC, the first 'SUPER' computer with a hard disk
drive (HDD). The HDD weighed over a ton and stored 5 MB of data.
Magnetic disk
Read/Write Head
surface of
magnetic tape and magnetic disks. Binary information is stored in the form of
tiny magnetized and non-magnetized spots on the surface of magnetic tape or
disk. A magnetized spot represents a binary 1 and a non-magnetized spot a
binary 0. A read-write head moves very close to the magnetic surface. The head
is able to detect and modify the magnetization of the material. Magnetic
storage is widely used because it is relatively cheap in comparison with other
storage technologies. The storage capacity is also very large, making it
attractive for storing very large amounts of data. The major limitation of
magnetic storage is that accessing the data can be quite slow. Hard disk is the
common example of magnetic memory as shown in Fig 1.39.
Fig. 1.39
Magnetic disk with read/write
Optical Memory
In optical
storage technology, a laser beam encodes digital data onto an optical disk in
the form of tiny pits and lands arranged in concentric tracks on the disk's
surface as shown in Fig. 1.40. A low-power laser scanner is used to
"read" data or information from these pits and lands, and converts it
to digital form.
Optical storage
provides cheaper and greater memory capacity than magnetic storage. An entire
set of encyclopedias, for example, can be stored on a standard 12-centimetre
(4.72-inch) optical disk. Optical disks include CDs, DVDs and Blu-ray
disks(BDs)
Fig.1.40
Optical Memory technology
1.6.3 Main
Memory
Main Memory
stores data and programs that are being executed by the computer. It also
stores the results produced by the ALU after processing the data. There are
three types of main memories on the motherboard which are ROM (Read Only
Memory), RAM (Random Access Memory) and Cache. These are known as main memory
or primary memory of computer.
ROM (Read Only
Memory)
ROM is a single
IC chip which is installed on the motherboard as shown in Fig. 1.41.
Fig.1.41 ROM
chip
It stores the
Basic Input/Output System (BIOS) of computer that controls input/output devices
and the start- up or boot process. BIOS programs test the computer's components
when it is turned on and then load the operating system into the RAM to make
the computer ready for operation.
BIOS programs
are permanently stored in ROM when it is manufactured. It is non- volatile
memory, that is, the programs stored in it are not lost when the computer is
turned off. There are three common types of ROM which are PROM (Programmable
ROM), EPROM (Erasable Programmable ROM) and EEPROM (Electronically Erasable
Programmable ROM).
RAM (Random
Access Memory)
RAM is high
speed memory installed on the motherboard. It is READ/WRITE memory. Information
can be read from or written into it. Programs are loaded into RAM from
secondary storage devices such as hard disk or USB flash drive for execution by
the microprocessor. It is volatile memory which means information stored in it,
is lost when the computer is turned off.
RAM modules are
installed in the memory slots on the motherboard. RAM modules are shown in
Fig.1.42.
Fig. 1.42 RAM
modules.
Cache Memory
Cache is a very
small amount of extremely fast memory inside the microprocessor or on the
motherboard. It is faster and more expensive than RAM. It stores information
that is most frequently used by the computer. The purpose of using cache is to
improve the processing speed of computer. There are three types of cache
memories which are Level 1 (L1), Level 2 (L2) and Level 3 (L3) as shown in
Fig.1.43. L1 cache is built inside the microprocess whereas L2 and L3 are on
the motherboard. L1 cache is faster than L2 and L3 cache.
Fig.1.43 L1, L2
and L3 Cache Memories
1.6.4 Volatile
and Non-Volatile Memory
Memory, on the
divided into two types: . volatile and non-volatile memory.
Volatile memory
Volatile memory
is a temporary memory, that requires power (electricity) to maintain the stored
information. Volatile memory retains the information as long as power supply is
on, but when power supply is off or interrupted the stored memory is lost. It is
also known as temporary memory. Examples of such memory are RAM (Random access
memory), Cache memory and Registers.
Non-Volatile
memory
Non-volatile
memory is a permanent memory, that can retain the stored information even when
powered off. Examples of non-volatile memory include ROM (Read-only memory),
flash memory, magnetic storage devices (e.g. hard disks and magnetic taps),
optical disks, and blue-ray disk. Non-volatile memory is typically used as
secondary storage for long-term or future use.
1.7 Computer
Software
Computer
software, often referred to simply as "software," is a collection of
programs, data, and instructions that tell a computer how to perform specific
tasks or functions. It is an important component of any computer system,
enabling it to process data, run applications, and interact with users.
Software is typically categorized into two main types: system software and
application software.
Computer
software can be classified into the following types.
·
System Software
·
Application Software
1.7.1 System
Software
System software
refers to a type of computer program that manages and controls the hardware
components of a computer system, as well as provides a platform for running
application software. It plays a crucial role in enabling interaction between
the user, application software, and the underlying hardware.
System software
serves as an intermediary between the user and the hardware, making it easier
for users to interact with and utilize computer systems effectively. The
following are some common types of system software.
Operating
System (OS):
The operating
system is a fundamental type of system software that manages hardware resources
and provides services for computer programs. It controls tasks such as process
scheduling, memory management, file system management, and hardware device
communication. Common examples of operating systems include Microsoft Windows,
macOS, Linux, and Android. Some common functions of OS include:
·
The OS facilitates user interaction
by providing a user-friendly interface.
·
It manages input/output operations.
·
It looks after the allocation of
tasks to the processor.
·
It handles the allocation and
deallocation of memory to programs.
·
It helps in organizing files and
directories, as well as provides mechanisms for storage and retrieval.
·
It manages peripheral devices, such
as printers and storage devices, and provides necessary device drivers.
·
It provides security and access
control through user authentications like User Identifications, passwords and
PINs etc.
Device Drivers:
Device drivers
are software components that facilitate communication between the operating
system and hardware devices like printers, graphics cards, and network
adapters. They ensure that the OS can interact with these devices correctly.
Utilities:
System
utilities are tools that help manage and maintain the computer system. They can
perform tasks such as disk cleanup, data backup, system monitoring, and virus
scanning. Examples include disk defragmenters, antivirus software, and system
diagnostic tools.
Compiler and
Assembler:
These tools are
essential for converting high-level programming languages (like C++, Java, or
Python) into machine code that the computer's processor can understand.
Compilers translate high level language code (source code) into executable
programs, while assemblers do a similar job for assembly language code.
High-level
Program Compiler Low-level Program
Linkers and
Loaders:
Linkers and
loaders are programs that help with the execute of programs. Linkers combine
multiple object files (compiled code) into a single executable file, while
loaders load these files into memory for execution.
Firmware:
Firmware is a
type of software that is permanently stored on hardware devices. It provides
low-level control over the device's operation. Examples include the BIOS (Basic
Input/Output System) in a computer's motherboard or the firmware in a digital
washing machine.
1.7.2
Application Software
Application
software, often referred to as "apps" or "software
applications," is a category of computer programs designed to perform
specific tasks or functions for computer users. Unlike system software, which
manages and controls the hardware and provides a platform for running
applications, application software is created to address the various needs and
requirements of users.
Some examples
of application software are:
·
Productivity Software
·
Business Software
·
Entertainment Software
·
Educational Software
Productivity
Software
Productivity
software is designed to help users perform tasks efficiently, organize
information, and create contents like documents, presentations, spreadsheets,
and databases. It includes software that facilitate office work, document
management, and collaboration.
Examples:
·
Microsoft Office Suite: Includes
applications like Microsoft Word (word processing), Excel (spreadsheets), and
PowerPoint (presentation).
·
Google Workspace: Offers tools like
Google Docs, Sheets, and Slides for online collaboration and document creation.
·
LibreOffice: A free and open-source
office suite with applications similar to Microsoft Office.
Business
Software
Business software
are specifically designed to meet the needs of businesses and organizations.
These software aim to streamline and enhance various aspects of business
operations, ultimately improving efficiency, productivity, and decision-making.
Examples:
• QuickBooks:
Accounting software for managing financial transactions and generating reports.
• Salesforce:
Customer Relationship Management (CRM) software for sales and marketing.
Trello: Project
management tool that helps teams organize projects.
Entertainment
Software
Entertainment
software is designed for leisure and enjoyment. It includes a wide range of
applications, from video games to multimedia players and streaming services.
Examples:
·
Minecraft: A popular game that
allows players to build and explore virtual worlds.
·
Spotify: A music application that
offers a vast library of songs and playlists.
·
Netflix: An online streaming service
for movies, TV shows, and documentaries.
Educational
Software
·
Educational software is created to
support learning and skill development. It includes a variety of applications
and tools that support educational activities, ranging from interactive
learning games to digital resources for teaching and assessment.
Examples:
·
Learning Management Systems (LMS): LMS platforms
provide a centralized place for educational content, resources, assessments,
and communication between educators and students. Some examples are AIOU Aaghi
LMS, Virtual Academy, FBISE LMS, etc.
·
Kahoot!: An online learning platform
that allows educators to create interactive quizzes and games for students.
·
Duolingo: Language learning app that
gamifies the process of learning new languages.
·
Scratch: A visual programming
language for teaching coding concepts to children.
1.1.1
Programming Languages
A programming
language is a structured and systematic method of communicating instructions to
a computer. It consists of a set of predefined commands, syntax, and rules that
allow programmers to write instructions, enabling the computer to perform
specific tasks or solve problems. It serves as a means of communication between
a human programmer and a computer, facilitating the development of software and
applications. Programming languages can be classified into two categories, that
is, low level languages and high-level languages.
Low Level
Languages
Low level
language is machine-oriented language. To understand low-level language,
detailed knowledge of internal working of computer is required. Low level
languages include machine language and assembly language.
Machine Language: Programming language that is directly understood by computer
hardware is known as machine language. Machine language is associated with
architecture of computer. Therefore, programs written in machine language for
one computer will not work on another because of design differences. It
consists of OS and 1S. It is almost impossible for humans to use machine
language because it entirely consists of numbers. Therefore, practically no
programming is done in machine language. Instead, assembly languages and high-level
languages are used.
Assembly Language: Assembly language consists of symbolic codes or abbreviations
known as mnemonics. It was developed to make computer programming easier than
machine language. The abbreviations used in assembly language make it easier to
learn and write programs compared to machine language. A program written in
assembly language must be converted into machine language before it is executed
by computer. A program known as assembler is used to translate assembly
language into machine language. Some important characteristics of Assembly
language are:
·
Assembly language allows programmers
to have access to all the special features of the computer they are using.
Certain types of operations which are not possible in high level languages are
easily programmed using assembly language.
·
Generally, a program written in
assembly language will require less storage and less running time than one
prepared in a high-level language.
·
Assembly languages are still the
best choice in some applications, but their use is gradually declining.
High-Level
Languages (HLLS)
High level
languages are English-oriented languages, and they are commonly used for
writing computer programs. These languages use English language words such as
print, goto, if, end, etc. Therefore, they are easy to learn and use. Some
examples of high-level languages are Visual Basic, C, Java and Pascal.
A program known
as compiler/interpreter is required to translate a high-level program into
machine language. Coding and debugging of a high-level language program is much
easier than a program written in a low level language.
High-level
languages can be classified into procedural, structured and object-oriented
programming languages.
Procedural and
Structured Languages
Procedural
programming is based upon the concept of modular programming. In modular
programming, programs are divided into smaller parts known as modules. Modular
programs consist of one or more modules. A module is a group of statements that
can be executed more than once in a program. Each module in a program performs
a specific task. It is easy to design, modify and debug a program in a
procedural language since it provides better programming facilities.
Structured
languages consist of three fundamental elements, which are sequence, selection,
and repetition.
Sequence: It means,
writing program statements in a logical sequence. Each step in the sequence
must logically progress to the next without producing any undesirable effects.
Selection: It allows the
selection of any number of statements based on the result of evaluation of a
condition which may be true or false. Examples of statements that implement
selection in programming are if, else-if, switch, etc.
Repetition
(loops): It
means executing one or statements a number of times until a condition is
satisfied. Repetition is implemented in programs using statements, such as for
and while loops.
Some examples
of structured and procedural languages are FORTRAN, Pascal, C, BASIC, ALGOL,
PL/1 and Ada Pascal.
Object-Oriented
Programming Languages
Object-oriented
programming (OOP) refers to a programming method that is based on objects such
as student, vehicle, building, etc. Object-oriented programming language
provides a set of rules for defining and managing objects. An object can be
considered a thing that can perform a set of activities. For example, the
object vehicle can be defined as an object that has number of wheels, number of
doors, color, number of seats, etc. The set of activities that can be performed
on this object include Steer, Accelerate, Brake, etc.
Complicated
large computer programs are difficult to design, develop, maintain, and debug.
The concept of object-oriented programming solves this problem. The most widely
used object-oriented programming languages are C++, Visual Basic, C#(known as C
Sharp) and Java.
Uses of
Low-Level Languages
Important uses
of low-level programming languages include:
|
Use |
Explanation |
|
Operating System Development |
Writing the core software that manages hardware resources. |
|
Device Drivers |
Creating software to enable communication with hardware devices. |
|
Embedded Systems |
Programming microcontrollers and loT devices for specialized
functions. |
|
Firmware Development |
Developing software that resides on hardware components. |
|
Real-Time Systems |
Ensuring precise timing and responsiveness in industrial control,
robotics, and aerospace systems. |
|
Security Tools |
Building intrusion detection, firewalls, and encryption software
for robust security. |
|
Game Development |
Optimizing game engines, physics simulations, and graphics rendering
for performance |
Uses of High-Level
Languages
Important uses
of high-level programming languages include:
|
Use |
Explanation |
|
Applications (Apps) Development |
Creating desktop, mobile, and web applications (Apps) for various
platforms. |
|
Web Development |
High-level languages are used to build websites, making them
interactive and functional. |
|
Data Analysis and Science |
Analyzing large datasets and conducting scientific research. |
|
Machine Learning and Al |
Developing machine learning models and Al algorithms. |
|
Automation and Scripting |
Automating tasks and processes, including system administration
and data manipulation. |
|
Game Development |
Developing gameplay logic, Al, and user interfaces for games. |
|
Database Management |
Creating, querying, and managing databases. |
|
Scientific and Engineering Simulations |
Simulating complex systems and conducting simulations. |
|
Business Software |
Developing enterprise-level software for various industries. |
|
Educational Tools |
Creating e-learning platforms and educational software. |
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Data Communication
Data
communication refers to the process of exchanging data or information (through
a computer network) between two or more devices or systems through a
transmission medium such as cables, optical fibers, or wireless mediums. This
communication can involve the transfer of various types of data, including
text, numbers, images, audio, and video, and it is a fundamental component of
modern information technology and telecommunications. A simple communication
network having wired and wireless connections is shown in Fig. 1.44.
Network
Communication Components
Data
communication is the process of transferring information from one point to
another in a networking environment. Network communication consists of five
basic components, as shown is Fig. 1.45.
Sender
Message
Medium
Protocol
Receiver
Sender
A
sender, also called a transmitter is a computer/device that sends the message
(data or information) from source to destination in a communication network. It
may be a computer, workstation, cell phone or camera. The sender device
converts the electrical signal into a form that is suitable for transmission
over the communication network.
Message
Message
is the data or information that is to be transmitted. Message can be in the
form of text, audio, video, or any combination of these.
Medium
Medium
is the path through which message travels from source to destination. A medium
can be wired, for example, telephone cable, coaxial cable, and fiber optics. It
can also be wireless for example Bluetooth, Wi-Fi, microwave, radio wave and
satellite.
Receiver
Receiver
is the device which receives transmitted message. It can be a computer,
workstation, telephone handset or television set. The data received from the
transmission medium may not be in proper form to be accepted to the receiver
and it must be converted to appropriate form before it is received.
Protocol
A
protocol is a set of rules that governs data communications. It represents an
agreement between the communicating devices. Without a protocol, two devices
are connected but may not communicating with each other.
Modes of Network Communication
Modes
of network communication refer to the methods or the ways information is
transmitted from one place to another.
The
following are different modes of data communication
Ø
Simplex, Half-duplex and Full-duplex
Ø
Synchronous and Asynchronous
Simplex Mode:
In Simplex
mode, the communication takes place in only one direction. In this mode
communication is unidirectional, i.e. the communication can only take place in
one direction and it is not possible for the receiver to send data back. For
example, data is sent to an electronic notice board found in train stations and
Airports as shown in Fig 1.46. Radio and television broadcastings are also
examples of simplex transmission.
Half-duplex mode:
In
half-duplex mode, the communication takes place in both directions but not at
the same time. The signal can only be sent or received at one time. A common
example of this type of communication is the use of walkie-talkies, as
Sender/Receiver shown in Fig. 1.47 where each of the persons communicating must
indicate when they have finished speaking. Half-duplex transmission is used
also in transaction-oriented systems, for example, communication between a
computer and a credit card machine.
Full-duplex
mode
In
full-duplex mode, the communication takes place in both the directions at the
same time. In this mode, both sender and receiver can send and receive the data
simultaneously. For example when two computers communicate with each other to
send and receive some data, as shown in Fig. 1.48. It is the fastest
bi-directional mode of communication. The full-duplex mode is like a two way
street, with traffic flowing in both directions at the same time. One common
example of full-duplex communication is the telephone network. When two people
are communicating by a telephone line, both can talk and listen at the same
time.
Asynchronous Transmission
In
asynchronous transmission, the time interval between two characters is variable
and not fixed as shown in Fig. 1.49. The computer devices can exchange
information at their own rate, slow or fast. Start and Stop bits are used in
asynchronous transmission. These bits provide timing (synchronization) for the
connection between the sender and the receiver. The start bit tells the
receiver that a character is coming and stop bit indicates that the
transmission of character has ended. This type of transmission is ideal for
slow-speed communication when gaps may occur during transmission. Example of
asynchronous transmission is keyboard data transmission.
Synchronous Transmission
In
synchronous transmission, the time interval between two characters is always
the same as shown in Fig.1.50. In this method two communicating devices are
synchronized and they continue to send characters in order to remain
synchronized, even if there is no data to be transmitted. A special
"idle" character is sent when there is no data for transmission. It
does not require transmission of start and stop bits. It sends data as one long
bit stream or block of data and each bit is sent one after the other. The
receiver counts the bits and reconstructs the sent information in bytes. It is
essential that timing is maintained as there are no start and stop bits and no
gaps. Accuracy is dependent on the receiver keeping an accurate count of the
bits as they come in.
Synchronous
transmission is faster than asynchronous because fewer bits have to be
transmitted; i.e. only data bits and no extra control bits are sent. The best
example of synchronous transmission is the data transmission between devices in
network communications links.
Communication Devices
A
device that is used in telecommunication systems for transmitting data from one
location to another is known as communication device.
Commonly
used communication devices are: Hub, Switch, Router and Gateway.
Hub
Hub
is a connectivity device used in LAN. It connects multiple LAN devices on one
network and makes them act together as a single network. A hub is
non-intelligent device and sends output to all the devices on the network. A hub
has multiple input/output (I/O) ports, in which an input in one port results in
it being an output in all the other ports, except the port where it was input.
A hub is shown in Fig. 1.51.
Switch
Switch
is a networking device that performs the same job as the hub but are considered
as intelligent than hub. It gathers information about the data packet and
forwards it to only the node (e.g. computer) it was intended for. A data packet
is a basic unit of communication over a computer network. When data is
transmitted, it is broken down into packets which are reassembled to the
original form once they reach the destination. A switch is shown in Fig. 1.52.
Router
Router
is a communication device which is used to connect two or more networks. Today,
most of the networks are connected to Internet. When the computer is sending
data to another computer on the Internet, router receives the data packets,
looks for the remote computer address and forwards it to a computer that is
closer to the remote computer. It forwards the data packets by selecting the
best path-way based on network traffic. Many routers take part in transmitting
the data packets from one location to another. A wireless router is shown in
Fig.1.53.
Gateway
Gateway is a
device that is used to connect a network to another network that uses different
protocols. If we have to link different kinds of networks, such as a network of
IBM mainframe computers and a network of PCs, we might have to use a gateway.
Gateways change the format of the data packets but not the contents of the
message, to make it conform to the application program of the remote computer.
A gateway is shown in Fig. 1.54.
Network Architecture
Network
architecture is the design of a communication system. It includes hardware devices
(such as routers and switches), cabling, network topology, and physical and
wireless connections. Computer networks consist of server computers and client
computers.
Server
Computer: A computer on the network that shares resources for others to use is
called a server computer or simply a server. Shared resources include
information, software, printer, plotter, Internet connection, hard disk, etc.
Client
Computer: A computer on the network that accesses resources that are shared by
other computers is known as a client computer or simply a client.
The
two commonly used network architectures are:
Client/Server
Network
Peer-to-Peer
Network
Client/Server Network
A
computer network in which each computer on the network acts as either a server
or a client is called a client/server or dedicated server network. Each server
computer on the network is called a dedicated server. Servers are not used as
client computers. Fig.1.55 illustrates how a dedicated server network may be
designed. The computer at the top of the figure is the dedicated server,
sharing files and applications. The remaining computers in the illustration are
clients that access resources shared by the server. Similarly, in a dedicated
server network, client computers never act as servers.
Client/Server
network includes one or more computers that are dedicated to acting as servers.
The servers are optimized to provide quick access to shared network resources.
Servers also provide centralized security to ensure that resources are not
accessed by unauthorized users.
Because
the client/server approach centralizes control of data and other shared
resources, one person or group is typically responsible for administering the
network.
Peer-to-Peer Networks
In
Peer-to-Peer networks, every computer is capable of playing the role of client,
server or both at the same time. In this network each computer on the network
is referred to as peer. In a peer- to-peer network, a peer computer can act as
both a server and a client at the same time. A peer computer on your desktop
can share files and printers with other computers and it can simultaneously
access other shared resources on the network. A conceptual view of a peer-to-
peer network is shown in Fig.1.56.
Peer-to-peer
networks tend to be relatively small. Most of these networks fall to range
between two and ten computers. Large peer-to-peer networks become difficult to
manage, because so many network administrators control sharing and maintaining
shared resources.
Types of Networks
The
following are different types of networks based on the size and physical area
they cover.
Local
Area Networks
A
Local Area Network (LAN) spans a limited physical area. It is confined to a
single building or a group of nearby buildings. LANs are used for sharing
applications, printers, group scheduling, e-mail, project tracking and other
tasks. A LAN is shown in Fig. 1.57.
Characteristics of LAN:
·
Spans a small physical area.
·
Uses high-speed wired/wireless
connections between computers.
·
It is a very reliable network.
Communication errors are very rare.
·
It consists of a limited number of
computers.
Wide Area Networks
A
Wide Area Network (WAN) spans a large physical area, connecting several sites
of an organization across cities, countries and continents. Because of the
longer distances involved, WANs are sometimes referred to as long-haul
networks.
A
WAN is often made up of two or more LANS connected together as shown in
Fig.1.58. For example, you might have a LAN at each site of your organization
and each of those LANS might be connected together to form a WAN.
Characteristics of WAN:
·
Spans a large physical area. It can
be worldwide like Internet.
·
Communication speed is slow compared
to LAN.
·
Connects computers through public
networks, leased lines or satellites. Connects multiple LANs.
·
Sometimes communication errors occur
due to its complexity.
Metropolitan Area Network
Metropolitan
Area Network (MAN) can span from several buildings or a large campus to entire
cities. MAN is used by many organizations. It also connects a number of local
area networks with high-speed communication lines.
Characteristics of MAN
• It
is larger than a LAN and smaller than a WAN. Covers an area of between 5 to 50
km diameter.
•
Uses fiber optic cable or microwave transmission.
•
Provides high-speed communication.
•
Used by telephone companies, Internet Service Providers and cable TV companies.
Virtual Private Network
Virtual
Private Network (VPN) is a computer network that provides remote access to
individuals and offices to their organization's networks. It provides cheap
communication by using public telecommunication infrastructure such as Internet
instead of expensive leased lines. It allows employees at home or on trip to
connect their laptops into the computer as office through public
telecommunication networks and do their work.
Characteristics of VPN
It
uses public networks such as Internet to connect computers. Provides secure
remote access.
Enables
files sharing, video conferencing and similar network services.
Provides
cheap communication over long distance.
Network Topologies
The arrangement
of network nodes (any devices which are part of network) and connections
between them is called the network's topology. A node represents any device on
the network. Topology is simply a map of the layout of nodes and connections in
the network. Four network topologies are popular today, namely, Bus, Star,
Ring, and Mesh.
Bus Topology
Bus
network topology connects each node to the network along a single piece of
cable, called a bus. Bus network topology is shown in Fig. 1.61.
Features of Bus Topology
·
Suitable for a small network.
·
Easy to connect a computer or a peripheral device to the network.
·
Requires less cable to implement.
·
Terminator is installed at each end of the cable to prevent signals
from reflecting back onto the bus and cause errors. Terminator is a device that
is attached to ground.
Limitations of Bus Topology
·
If the single cable is damaged or
broken at any point, the entire network can go down.
·
Difficult to identify the problem if
the entire network goes down.
·
Not suitable for large network.
Star Topology
In a
star network topology, each network node is connected to a central device
called a hub. Large networks can require many hubs and hubs can be connected to
each other to create a single large network. Star network topology is shown in
Fig. 1.62.
Features of Star Topology
·
It is suitable for both small and
large networks.
·
Easy to install and wire.
·
Easy to detect and remove faults.
·
Failure of cable does not stop the functioning
of the entire network.
Limitations of Star Topology
·
Failure of the hub causes the entire
network to go down.
·
Expensive topology to implement.
Lengthy cable with a hub is required to install star topology
Ring Topology
Ring
topology is shaped just like a ring. It is made up of an unbroken circle of
network nodes. Ring network topology is shown in Fig. 1.63.
Features of Ring Topology
·
Each node is directly connected to
the ring.
·
Easy to install and wire.
·
Data on the network flows in
·
direction.
·
Not costly to implement.
Limitations of Ring Topology
·
If the ring is broken at any point,
the entire network stops functioning.
·
Slower than other network
topologies.
Mesh Topology
In
mesh topology, each node is directly connected to all the nodes as shown in
Fig.1.64.
Features of Mesh Topology
·
Most reliable network topology.
·
Data can be routed around failed
computers or busy ones.
·
Can manage high traffic.
Limitations of Mesh Topology
·
Most expensive topology to
implement.
·
Setup and maintenance is very
difficult.
Data Communication Standards
Data
communication standards are a set of rules (protocols and specifications) that
define how data is transmitted, received, and processed in computer networks
and communication systems. These standards ensure that devices and systems from
different manufacturers can communicate and work together flawlessly. Data
communication standards play a crucial role in enabling interoperability,
reliability, and efficiency in the exchange of data.
The
OSI (Open Systems Interconnection) is one such standard conceptual framework
used in the field of computer networking to define and understand how different
networking protocols and technologies interact and work together.
OSI Model
The
International Standards Organization (ISO) based in Geneva, developed standards
for international and national data communications. In the early 1970s, ISO
developed a standard model of a data communication system and called it the
Open Systems Interconnection (OSI) model.
The
OSI model consists of seven layers. Each layer performs a specific task during
data communication as shown in Fig. 1.65.
The
seven layers of OSI model are described below.
Layer 7-Application Layer
Application
Layer provides services to end-user. It interacts with the operating system or
application software whenever the user wants to send files, read messages or
perform other network related activities.
Layer 6 - Presentation Layer
Presentation
Layer takes the data provided by the Application Layer and converts it into a
standard format that the other layers can understand. At the receiving end it
also formats the information so that it looks the way the user can understand.
Layer 5 - Session Layer
Session Layer
performs functions that enable two applications or two pieces of the same
application to communicate across the network. It performs security, name
recognition, logging and other similar functions. It also establishes,
maintains, and ends communication with the receiving computer.
Layer 4 - Transport Layer
Transport
Layer establishes connections between two computers on the network. It handles
quality control by making sure that the data received is in the right format
and the right order.
Layer 3 - Network Layer
Network
Layer decides which physical path-way the data should take to reach the
destination. The communication device Router works in network layer.
Layer 2 - Data Link Layer
Data
Link Layer defines the format of data on the network. This layer converts the
data into packets and checks them before putting them on the path-way. The
communication device Switch works in this layer.
Layer 1 - Physical Layer
Physical
Layer defines cables and signaling. It provides hardware means such as cables
and connectors for sending and receiving data. Cables, hubs and repeaters work
in this layer.
Data Communication Protocols
Different
communication protocols define how data is transmitted and received over a
network. Examples include:
·
TCP/IP (Transmission Control
Protocol/Internet Protocol): Used for internet communication and provides
reliable, connection-oriented data transfer.
·
HTTP (Hypertext Transfer Protocol):
Used for transferring web pages and related data on the World Wide Web.
·
FTP (File Transfer Protocol): Used
for transferring files between computers on a network.
·
SMTP (Simple Mail Transfer
Protocol): Used for sending email messages.
The Internet
The
Internet is a global network of interconnected computer networks that allows
for the exchange of data, information, and communication among users and devices
across the world. It is a vast and decentralized network that spans continents
and connects billions of computers, servers, and other devices.
Evolution of the Internet
The Internet
has evolved from its origins in the 1960s as ARPANET, a U.S. Department of
Defense project for research institutions and military installations, to become
a global network of interconnected computer networks. In the 1970s, the
development of TCP/IP protocols established the foundation for the modern
Internet, allowing different networks to communicate. The 1990s saw the
emergence of the World Wide Web and web browsers, revolutionizing how people
access and share information over the Internet. The 2000s brought broadband
internet and social media platforms, while the 2010s saw the rise of mobile
internet and the Internet of Things (IoT). In the 2020s, the Internet continues
to evolve with cloud computing, artificial intelligence, and 5G technology,
impacting nearly every aspect of modern life.
Working of the Internet
The Internet is
the largest computer network ever built. It globally connects billions of
devices and networks. It operates through a decentralized architecture using
packet- switching technology. Data is divided into packets, which are routed
through a network of interconnected routers and switches. Protocols like TCP/IP
ensure data is packaged, addressed, and transmitted correctly. The Domain Name
System (DNS) translates human- readable domain names (e.g., www.ncc.gov.pk)
into IP addresses. Content is hosted on servers, and data is transmitted as
packets to and from these servers. As data travels through the network, it is
encapsulated in headers at each layer of the OSI model (such as the IP and TCP
headers). When the data reaches its destination, these headers are removed
through a process called de-capsulation. Security measures like encryption protect
data during transmission. The Internet's interoperable design allows diverse
devices and networks to communicate, making it a global information and communication
platform.
Advantages of the Internet
The
main advantages of the Internet include:
·
Global Connectivity: Enables
communication and access to information worldwide.
·
Vast Information: Provides a
vast information resources and knowledge.
·
Communication: Facilitates
real-time communication and collaboration.
·
E-commerce: Allows online
shopping and digital transactions.
·
Education: Supports
online learning and research.
·
Business: Enhances
productivity and global reach.
·
Entertainment: Offers
streaming, gaming, and social media.
·
Innovation: Promotes
technological advancements and research.
Disadvantages of the Internet
The
main disadvantages of the Internet include:
·
Privacy Concerns: Threats to
personal data and online privacy. Cybersecurity Risks: Vulnerability to hacking
and cyberattacks.
·
Information Overload: Overwhelming
amount of data and misinformation.
·
Digital Addiction: Excessive
screen time and online dependency.
·
Digital Divide: Unequal access
to the Internet worldwide.
·
Online Harassment: Cyberbullying
and harassment issues.
·
Health Concerns: Physical and
mental health impacts.
Common Applications of the Internet
Main
applications of the Internet include:
·
Communication: Email,
messaging, and video calls.
·
Information Retrieval: Web browsing,
search engines, and online databases.
·
E-commerce: Online
shopping, banking, and digital payments.
·
Social media: Networking,
content sharing, and social interaction.
·
Entertainment: Streaming,
online gaming, and multimedia content.
·
Education: Online
courses, research, and e-learning platforms.
·
Research and Innovation: Access to
research materials and innovation platforms.
·
Business and Work: Remote work,
collaboration, and e-commerce.
Summary of Computer Systems
Computer
systems: are an integral part of modern life, transforming work, communication,
learning, and entertainment. They consist of intricate hardware and software
components that collaborate to process information and accomplish various
tasks.
Abacus:
The Abacus, invented by the Chinese 4000 years ago, was a wooden frame with
metal rods and beads used for simple arithmetic calculations.
Napier's
Bone: John Napier developed Napier's bones, which used 9 strips marked with
numerals for multiplication and division, introducing the decimal point system.
Pascaline:
Blaise Pascal's 1642 invention, the Pascaline, was first mechanical calculator,
consisting of gears and wheels.
Stepped
Reckoner or Leibniz Wheel: Wilhelm Leibniz improved Pascal's device in 1673,
creating the digital mechanical known as the stepped reckoner using grooved
wheels.
Difference
Engine: Charles Babbage's early 1820s invention, the Difference Engine, was a
steam-powered calculating machine for basic computations.
Analytical
Engine: Charles Babbage's Analytical Engine in 1830 was a mechanical computer
that used punch cards, capable of solving complex mathematical problems and
storing data.
Tabulating
Machine: Herman Hollerith's 1890 invention, the Tabulating Machine, based on
punch cards, computed statistics and recorded data, leading to the creation of
IBM in 1924.
Differential
Analyzer: In 1930, Vannevar Bush introduced the first electrical computer, the
Differential Analyzer, using vacuum tubes for calculations at a rate of 25 per
minute.
Mark
I: Howard Aiken's Mark I, a digital computer invented in 1944, could add
eight-digit numbers and print results using punched cards; it was 50 feet long
and weighed 5 tons.
First
Generation Computers (1940-1956): First-generation computers used vacuum tubes,
were slow, expensive, and huge, relied on punched cards, and had limited
memory.
Second
Generation Computers (1956-1963): Transistors replaced vacuum tubes in
second-generation computers, increasing speed, and reliability, and reducing
size and cost.
Third
Generation Computers (1963-1971): Third-generation computers used integrated
circuits (ICs) instead of transistors, consuming less power and introducing
keyboard and monitor interfaces.
Fourth
Generation Computers (1971 - Present): Fourth-generation computers introduced
microprocessors, becoming faster, and smaller, and supporting advanced
input/output devices, modern programming languages, and multimedia software.
Fifth-Generation
Computers: Fifth-generation computers aim to understand natural languages and
possess thinking capabilities, relying on Artificial Intelligence (AI) and
enabling user commands in any language.
•
System: A system is a collection of interconnected components working together
to achieve specific purposes, found in various aspects of life.
•
Natural Systems: Natural systems exist in nature, are diverse, and
self-regulate.
•
Examples of Natural Systems: Ecosystems, weather systems, geological systems,
hydrological systems, and the solar system.
Artificial
Systems: Human-made systems designed to solve problems.
•
Examples of Artificial Systems: Communication systems, information systems,
transportation systems, energy systems, manufacturing systems, and healthcare
systems.
Input
Devices: Used to provide data to the computer, including keyboards, mice,
microphones, scanners, barcode readers, digital cameras, and touch screens.
System Unit: The central part of a computer, including the motherboard,
microprocessor (CPU), and registers.
Memory
Types: Computer memory includes ROM, RAM, and cache memory, each with specific
functions and retention properties.
Output
Devices: Display text, graphics, and images, including monitors, printers,
plotters, and speakers.
Data
Transmission: Data moves between components through buses, following an
instruction cycle that fetches, decodes, executes, and stores data.
Von
Neumann Architecture: Explains how computer hardware and software work
together, comprising a CPU, registers, ALU, control unit, and buses.
•
Memory Units: Memory is measured in bytes, with various units like kilobytes,
megabytes, gigabytes, terabytes, petabytes, and exabytes.
•
Memory Built-up: Memory can be chip, magnetic, or optical, and memory retention
power categorizes it as volatile or non-volatile.
•
Chip Memory: Fast memory used in various devices like RAM, ROM, cache, and
SSDs.
•
Magnetic Memory: Uses magnetized mediums like hard disks and magnetic tapes to
store data.
•
Optical Memory: Stores data as pits and lands on optical disks like CDs, DVDs,
and Blu-ray disks.
•
Volatile Memory: Requires power to retain data, examples include RAM, cache,
and registers.
•
Non-Volatile Memory: Retains data even without power, including ROM, flash
memory, and storage devices like hard disks and optical disks.
Computer
Software: Computer software is a collection of programs, data, and instructions
enabling computers to perform tasks.
System
Software: Manages and controls hardware, acting as an intermediary between
users and hardware. Includes operating systems, device drivers, utilities,
compilers, assemblers, linkers, loaders, and firmware.
Application
Software: Designed for specific user tasks, such as productivity, business,
entertainment, and education. Examples include word processors, spreadsheet
software, games, and educational programs.
Programming
Languages: Programming languages instruct computers to perform tasks. Low-level
languages (machine and assembly) are hardware-oriented, while high-level
languages (e.g., C++, Java) are user-friendly. High-level languages can be
procedural, structured, or object-oriented.
Data
Communication: Involves exchanging data between devices or systems via
networks. Key components include sender, message, medium, protocol, and
receiver.
Modes
of Network Communication: Modes include simplex (one-way), half- duplex (both
ways, not simultaneously), and full duplex (both ways simultaneously).
Transmission can be asynchronous (variable timing) or synchronous (fixed
timing).
Communication
Devices: Common devices include hubs, switches, routers, and gateways. Each
serves specific roles in network communication.
Network
Architecture: Includes LANs (local), WANS (wide), MANS (metropolitan), and VPNs
(virtual private). Defines the physical layout and connectivity of a network.
Network
Topologies: Topologies dictate how nodes are connected; options include bus,
star, ring, and mesh. Each has unique features and limitations.
Data
Communication Standards: Standards (like OSI) establish rules for data
transmission, ensuring compatibility and reliability in networks and systems.
OSI
Model: The OSI model, developed by ISO, consists of seven layers that perform
specific tasks in data communication, including Application, Presentation,
Session, Transport, Network, Data Link, and Physical layers.
Data
Communication Protocols: Various communication protocols, such as TCP/IP, HTTP,
FTP, and SMTP, define how data is transmitted and received over networks.
Internet:
The Internet is a global network of interconnected computer networks that has evolved
from ARPANET to the modern era, facilitating communication, information
exchange, and connectivity worldwide.
Working
of the Internet: The Internet operates through a decentralized architecture,
using packet-switching technology, protocols like TCP/IP, DNS for domain
translation, and security measures to transmit and protect data.
Advantages
of the Internet: The Internet offers global connectivity, vast information
resources, real-time communication, e-commerce, education, business
opportunities, entertainment, and innovation.
Disadvantages
of the Internet: Concerns related to privacy, cybersecurity risks, information
overload, digital addiction, the digital divide, online harassment, and health
impacts are associated with the Internet.
Common
Applications of the Internet: The Internet is used for communication,
information retrieval, e-commerce, social media, entertainment, education,
business, research, and innovation.
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