Information Systems Technology Chapter Three

CHAPTER THREE
Information Systems
Technology

Information Systems Technology
 Contents of Presentation
– Computer Hardware
– Computer Software
– Telecommunications
– Database Management

Computer Hardware
1) Technological Evolution of Computers
– Computers changed over time, they improved in
speed, power, and efficiency.
– Those changes are recognized as a
progression of generations of discoveries,
each characterized by specific developments.

Computer Hardware…Cont’d
 First Generation (1951-1959)
– The early first generation computers were
powered by thousands of vacuum tubes.
– The computers were large because of the
massive number of tubes required to operate the
machines.
– The tubes themselves were large; they required a
lot of energy and generated a great deal of heat.
– The maximum memory size was only about 2KB,
with speed of 10,000 instructions per second.

First Generation…Cont’d
– Data were entered into the computer on punched
cards.
– The computer's memory was stored on magnetic
tapes and drums.
– Output consisted of punched cards or paper.
– Binary (machine) and assembly languages were
used to program the computers.
– Human operators physically had to reset relay
switches and wiring before a program could be
run.

Second Generation (1959-1965)
 The Transistor technology characterized the
second- generation computers.
 A transistor was made of a semi conducting
material, and it controlled the flow of electricity
through the circuits.
 A breakthrough in technology, the transistor
made it possible to produce a computer that was
faster, physically smaller, more powerful, and
more reliable than before.
 Transistors were smaller, less expensive,
required less electricity, and emitted less heat
than vacuum tubes.

Second Generation…Cont’d
 Fewer transistors than tubes were required to
operate a computer.
 They were not as fragile as vacuum tubes, and
they lasted longer.
 Memory size expanded to 32 KB of RAM, and
speeds reached 200,000-300,000 instructions
peer second.
 Magnetic tape most common external storage,
but magnetic disk introduced.
 Punched cards and magnetic tape for input.

Second Generation…Cont’d
 Punched cards and paper for output.
 Programming languages also became more
sophisticated. High-level languages that
resembled English, including FORTRAN,
COBOL, BASIC, etc. were being developed.
 Like the first-generation computers, second-
generation computers were primarily under the
control of human operators.
– Human operator needed to handle punched
cards

Third Generation (1965-1971) Integrated
circuit technology
 The use of integrated circuits (ICs) signified the
beginning of third-generation computers.
 Again, they were smaller, more efficient, and more
reliable than their predecessors.
 Memory technology was improved.
 By 1969, as many as 1000 transistors could be built on
one chip of silicon.
 Magnetic disks had been improved and were being used
more for storage.
 Memory expanded to 2MB of RAM and processing
speed accelerated to 5 MIPS.

Third Generation…Cont’d
 Monitors and keyboards were introduced for data
input and output.
 A new computer program, the operating system,
effectively controlled the computer and its resources.
 Human operators were no longer required, and
processing could be done at "computer speeds"
rather than "human speeds".
 High-level programming languages continued to be
developed such as Pascal.

Third Generation…Cont’d
 Another phenomenon of this third generation involved the
introduction of a concept of computer families.
– Prior to this concept, businesses would buy computers and
programs only to find that almost before the system was fully
adapted, it was outdated ,or unable to grow with the user's needs.
– IBM recognized this problem and created an entire product line,
the IBM/ 360 series, which allowed for necessary upgrading or
expansion.
– Programs written for one computer were compatible with any of
the machines in the line.
 Minicomputers used commercially (Nov. 1963). Were
substantially cheaper than mainframes.

Fourth Generation (1971-present) LSI and
VLS Integrated circuit technology.
 The significant distinction for the fourth-generation
computers is the development of large-scale
integration (LSI) circuits.
– LSI placed several thousand transistors on to a single chip
 This advancement was followed in the mid-1970s by
the development of very large-scale integration
(VLSI), the incorporation of several hundred
thousand transistors on to a single chip. (contain
from 200,000- 1 million circuits per chip).

Fourth Generation…Cont’d
 VLSI made the development of the first
microprocessor, and thus the microcomputer,
possible. This development was followed by the
creation of faster, more powerful microprocessors
such as the Intel 80386.
 Magnetic disks became the primary means of
external storage.
 Fourth-generation languages emerged and
application software for microcomputers became
popular.

2) The computer system concept
– A computer is a system - an interrelated
combination of components that performs the
basic system functions of input, processing,
output, storage and control, thus providing end
users with a powerful information processing tool.

a) Types of Computer systems
– Today's computer systems display striking differences as
well as basic similarities.
– Computer systems are typically classified as
microcomputers, minicomputers, mainframes, and
supercomputers.
– such categories are attempts to describe the relative
computing power provided by computers. Computers may
differ in their processing speed, and memory capacity, as
well as in the number and capabilities of peripheral
devices for input, output, and secondary storage they can
support.

Types of Computer systems
 Microcomputer systems
– Microcomputers are the smallest but most
important category of computer systems for
end users.
– Also called personal computers (or PC)
– Microcomputers come in a variety of sizes and
shapes for a variety of purposes.

 Microcomputer systems
– Most common size classification include: desktop,
portable, laptop, transportable, handheld.
– Use classification: Single- user, multi-user.
– The typical hardware components of
microcomputer include: Main microprocessors,
Several support microprocessors and associated
control, Primary storage, input/output devices,
and, secondary storage devices.

 Minicomputer systems
– Are midrange systems that are larger and more
powerful than most microcomputers but are
smaller and less powerful than most mainframe
computer systems.
– High-end models of microcomputers more
powerful than some minis
– High-end models of minis more powerful than
some smaller models of mainframes.

 Mainframe computer systems
– are large, powerful computers that are
physically larger than micros and minis,
and usually
 have one or more central processors with
faster instruction processing speeds (from 10-
200 MIPS)
 have large primary storage capacities (can
range from 32 MB -500 MB)

can serve hundreds of users at once
– process hundreds of different
programs
– handle hundreds of different
peripherals for hundreds of users at
the same time.

– mainframes are used by major corporations and
government agencies
 national banks
 complex calculations in scientific and engineering
analyses
 simulation of complex design projects such as aircraft
design.
 stock exchanges

 Supercomputer systems
– Are extremely powerful mainframe computer
systems specifically designed for high-speed
numeric computation
– A small number of large supercomputers are
built each year for government research
agencies, military defense systems, national
weather forecasting, etc.

b) The central processing unit (CPU)
– The CPU is the most important hardware
component of a computer system.
– The CPU is subdivided into three major units:
the ALU, the control unit, and the primary
storage unit.
 The control unit obtains instructions from those
stored in the primary storage unit and interprets them.
Then, it transmits directions to the other components
of the computer system, ordering them to perform
required operations.

The central processing unit (CPU)
 The arithmetic-logic unit (ALU) performs required
arithmetic and comparison operations.
– A computer can make logical changes from one set of
program instructions to another based on the results of
comparisons made in the ALU during processing.
– The basic arithmetic operations include addition,
subtraction, multiplication, and division. Software can be
used to combine these four basic math functions to perform
logarithmic, trigonometric, and other mathematical
functions.
– A logic operation is one where numbers or conditions are
compared to each other. Examples of logic functions are
greater than, equal to, not equal to, greater than or equal to,
and less than or equal to.

 The primary storage unit (or main memory)
– refers to the internal storage of the computer, where
programs and their data are stored.
– provides temporary storage during program execution. Part
of primary storage also contains permanently stored
instructions that tell the computer what to do when it is
turned on.
– Because primary storage is located inside the computer and
is linked directly to the other components of the CPU,
access time to data is very fast.

– RAM- random access memory - is used for short-
term storage of data and /or program instructions.
 located physically closer to the processor
 the contents of RAM can be read and changed when
required.
 RAM is volatile- this means that if the computer's electric
supply is disrupted or the computer is turned off, its
contents will be lost

– ROM- read only memory- is another kind of memory found
in a computer, which stores important program instructions
permanently.
 The contents of ROM can be read, data cannot be written into
it.
 ROM contains information on how to start the computer.
 The actual contents of ROM are usually set by the computer
manufacturer; they are unchangeable and permanent.
 ROM is nonvolatile- because its contents cannot be altered
and they are not lost when the electric current is turned off.

c) Input and output devices
(1) Input devices
 Before data can be processed by the computer, they must be
translated into a machine-readable form and entered into the
computer by an input device.
– We have a variety of input devices:
 Keyboard - the most widely used input device.
 Electronic mouse
 touch screens
 light pens
 scanners
 voice recognition

(2) Output devices
 Output is the process of translating data in machine-
readable form into a form understandable to humans or
readable by other machines.
 The information that is the result of processing is also
often referred to as output.
 Output device is a peripheral device that allows a
computer to communicate information to humans or
another machine by accepting data from the computer
and transforming them into a usable form.

 Output is divided into two general categories:
– output that can be readily understood and used
by humans.
– output to secondary storage devices that hold the
data to be used as input for further processing by
a computer or for use by another machine.
 Human readable output can in turn be categorized
as:
– Hard copy - is output such as paper that can be read
immediately or stored and read later.
– Soft copy - is usually a screen-displayed output.

– Video display monitors and printers are
the most widely used output devices in
microcomputer systems.
 Other devices, such as audio speakers,
graphics plotters are also used.

d) Secondary storage devices
– Because primary storage may not be large
enough to hold all the required instructions and
data, and because RAM is volatile and doesn't
provide long-term memory, supplemental storage
is necessary.

 Secondary storage is the nonvolatile memory
that is stored externally to the computer
– This medium is usually used for the storage of
large amounts of data for permanent or long-term
storage of data.
– Is also used for storing backups, or copies, of
data and programs so that they are not
permanently lost if primary storage power is
interrupted.

 Three secondary storage media used with all
sizes of computers are: magnetic tapes,
magnetic disks, and optical disks.
 While these media can hold much more data
than primary storage, access to the data is
slower.

Secondary storage devices
 Magnetic tapes
– Store records or groups of related data, sequentially, i.e.
one after another. To get to the data you're looking for,
every record preceding them must be read.
– Can store large quantities of data inexpensively and so are
often used as backup storage media (for security purposes).
– Are re-erasable, reusable, and durable. They can easily be
cataloged and stored in a tape library.
– However, a magnetic tape is not well suited for data files
that are revised or updated often. These files should be
stored on a medium where access to data is faster and
more direct.

 Magnetic disks
– Are the most common form of secondary storage
for modern computer systems.
– A magnetic disk's main advantages over
magnetic tape include:
 The ability to access the data stored in it directly.
 The ability to hold more data in a smaller space.
 The ability to attain faster data transfer
– The two basic types of magnetic disk media are
hard disks, and floppy diskettes.

 Floppy diskettes
– A floppy diskette is a small flexible Mylar disk coated
with iron oxide on which data are stored.
– Mostly available in two sizes
 31/2 inch microfloppy
 5 1/4 inch diskettes
– A diskette must be prepared for use before data or
programs can be stored on it.
– Each diskette, regardless of size, is divided into
concentric circles called tracks where data are stored.

 The diskette is also divided into pie-shaped wedges
called sectors.
 The number of tracks and sectors is usually
determined by the computer's operating system
during a formatting operation. The operating system
labels each sector of each track with an address so
that the computer can go directly to a specific area,
rather than starting at the beginning, as with
magnetic tape.

 A Floppy diskette may be
 Single- sided, in which case data are recorded on
only one side of the diskette; or
 Double-sided, in which case data can be recorded in
both sides of the diskette.

 Hard disks
– A hard disk is just that - hard and inflexible. It is
made from materials such as aluminum.
– The I/O device used to transfer data to and from a
hard disk is called a hard-disk drive.

 Hard disks
– The hard disk has several advantages over a
floppy disk.
 The rigid construction of a hard disk allows it to be
rotated very fast (3,600 rpm) as compared to a floppy
diskette (360 rpm). Thus, data can be transferred much
faster to or from a hard disk because it takes less time to
find the storage location.
 This disk allows data to be stored more densely. More
data can be placed in a smaller area giving the hard disk
more storage capacity than a floppy diskette of the same
size.

 Optical disks
– An optical disk is a disk on which data are recorded and
read by laser beams rather than magnetic means.
– Such disks can store data at densities much greater than
magnetic disks.
– The optical disk system most often used with
microcomputers is called CD-ROM; it is a form of read-only
storage in that data can only be read from it, not written to it.
– Other optical disk technologies produce WORM (write once,
read many) and CD-R (compact disk recordable) disks. This
allows computers with the proper optical disk drive units to
record their own data once on an optical disk, then be able
to read it indefinitely.

 The major limitation of CD-ROM, CD-R, and
WORM disks is that recorded data cannot be
erased.
 However, erasable optical disk systems have
become available. This technology records
and erases data by using a laser to heat a
microscopic point of the disk’s surface.

Computer Software
a) Software programs
– Software refers to the detailed instructions that control
the operation of a computer hardware.
– Without the instructions provided by software, computer
hardware is unable to perform any of the tasks we
associate with computers.
– A software program is a series of statements or
instructions to the computer.
 The process of writing or coding the program is called
programming, and the individual who performs this task is
called a programmer.

Software programs…Cont’d
 In order to execute, or have its instructions
performed by the computer, a program
must be stored in the computer's primary
storage along with the required data.
 This is called the stored- program concept.
 Once a program has finished executing, the
computer hardware can be used for another
task by loading a new program into primary
storage.

Computer Software…Cont’d
b) Major types of software
– There are two major types of software: systems
software and application software.
– Systems software.
 Consists of programs that control and direct the operation
of the computer hardware. That is, it consists of programs
that manage computer resources such as the CPU,
printers, terminals, etc.
 Systems software consist of programs that coordinate the
various parts of a computer system and mediate between
application software and computer hardware.

Major types of software…Cont’d
 Application software
 Application software consists of programs
designed for applying the computer to solve a
specific problem.
 It helps the user and the system software work
together.
 Systems software provides the platform on
which applications software runs.

 The relationships among system software,
application software, hardware, and the user
are illustrated in the next slide.

Computer
hardware
System software
Application software
End users

I. System software
– Consists of computer programs that manage
and support a computer system and its
information processing activities.
– These programs serve as a vital software
interface between computer system, hardware
and the application programs of users.
– Such programs can be grouped into three
major functional categories:

 System management programs
– programs that manage the hardware, software,
and data resources of the computer system
during its execution of the various information
processing jobs of users.
– Major system management programs are
operating systems, database management
systems, and telecommunications monitors.

 System support programs
– Programs that support the operations and
management of a computer system by providing a
variety of support services.
– Major support programs are system utilities,
performance monitors, and security monitors.

 System development programs
– Programs that help users develop information
system programs and procedures and prepare
user programs for computer processing.
– Major development programs are language
translators, programming tools, and CASE
packages.

System management programs
a) Operating Systems
– The most important system software package for any
computer is its operating system.
– An operating system is an integrated system of programs
that manages the operations of the CPU, controls the
input/output and storage resources and activities of the
computer system, and provides support services as the
computer executes the application programs of users.
– The primary purpose of an operating system is to
maximize the productivity of a computer system by
operating it in the most efficient manner.

System management programs…Cont’d
 An operating system minimizes the amount of
human intervention required during processing.
 Examples of popular microcomputer operating
systems are Ms-Dos, OS/2, Macintosh for apple
computers, XENIX, Windows 95,98 .
 An operating system performs five major
management functions in the operation of a
computer system. They are discussed Next.

System management
programs…Operating Systems
(1) Task management
– the task management programs of an
operating system manage the
accomplishment of the computing tasks of
end users.
– They give each task a slice of a CPU's time
and interrupt the CPU operations to substitute
other tasks.

System management
 Task management may involve a multitasking
capability where several computing tasks can occur
at the same time.
 Multitasking may take the form of
– multiprogramming, where the CPU can process the tasks
of several programs at the same time, or
– time-sharing, where the computing tasks of several users
can be processed at the same time.

System management
(2) Resource management
– Involves controlling the use of computer system
resources by database management,
telecommunications, and other system software
and by the application software programs
executed by the computer system.
– These resources include primary storage,
secondary storage, CPU processing time,
input/output devices.

System management
(3) File Management
– An operating system contains file management
programs that control the creation, deletion, and
access of files of data and programs
– File management also involves keeping track of
the physical location of files on magnetic disks
and other secondary storage devices.

System management
(4) Providing a user Interface
– The user interface is the part of the operating
system that allows you to communicate with it so
you can load programs, access files, and
accomplish other tasks.
– Three main types of user interfaces are:
 Command- driven
 Menu- driven
 Graphical -user interfaces.

System management
(5) Utilities and other functions
– Provide a variety of support services.

System management programs…DBM
Systems
 Database Management System (DBMS)
– is a set of computer programs that controls the creation,
maintenance, and use of the databases of users and
computer using organizations.
– is a system software package that helps you use the
integrated collections of data records and files known as
databases.
– Examples of popular mainframe packages are DB2 by IBM
and Oracle by Oracle corporation.
– Examples of microcomputer packages are dBase by Ashton
Tate, FoxPro by FoxPro and R: Base by Microrim.

Systems
 Most DBMS packages can perform four primary
tasks:
– Database creation
 Define and organize the content, relationships, and structure of
the data needed to build a database.
– Database interrogation
 Access the data in a database to support various information
processing assignments.
 This typically involves information retrieval and report
generation. Thus, you can selectively retrieve and display
information and produce printed reports and documents.

Systems
– Database Maintenance
 Add, delete, update, correct, and protect the data in a
database.
– Application development
 Develop prototype of data entry screens, queries, forms,
reports and labels for a proposed application.

System management
programs…Telecom Monitors
 Telecommunications Monitors
– Modern information systems rely heavily on
telecommunications networks, which provide electronic
communication links between end user workstations, other
computer systems, and databases.
– This requires control programs called telecommunications
monitors. They are used by a main computer (called the
host) or in telecommunications control computers such as
front-end processors and network servers.

System management
programs…Telecom Monitors
 Telecommunications monitors and similar
programs perform such functions as
 connecting or disconnecting communication
links between computers and terminals,
 automatically checking terminals for
input/output activity,
 assigning priorities to data communication
requests from terminals, and
 detecting and correcting transmission errors.

System support programs
 System utilities
– Perform miscellaneous housekeeping and file conversion
functions. (sorting operations, clearing primary storage,
load programs, etc.)
 system performance monitors
– Programs that monitor the performance and usage of
computer systems to help its efficient use.
 system security monitors
– Monitor and control the use of computer systems and
provide warning messages and record evidence of
unauthorized use of computer resources.

System development programs
 Programming Languages
– machine languages
– assembler languages
– high-level languages
– fourth-generation languages

System development programs…Cont’d
 Language Translator programs
– Computer programs consist of sets of instructions
written in programming languages, such as
COBOL, BASIC, or Pascal which must be
translated into the computer's own machine
language before they can be processed by the
CPU.
– Programming language translator programs are
known by a variety of names.

 Language Translator programs
– An Assembler- translates the symbolic instruction codes of
programs written in an assembler language into machine
language instructions.
– A compiler- translates high-level language statements.
– An interpreter- is a special type of compiler that translates
and executes each program statement one at a time,
instead of first producing a complete machine language
program, like compilers and assemblers do.

 A program written in a language such as
BASIC or COBOL is called a source
program.
 When the source program is translated into
machine language, it is called the object
program.
 The computer executes the object program.

 Application software
– Includes a variety of programs that can be
subdivided into general-purpose and
application-specific categories.
– General purpose application programs are
programs that perform common information
processing jobs for end users.
 word processing programs
 spreadsheet programs
 Graphics packages

 Application-specific programs
– Major categories of application specific programs
are:
 Business application programs- programs that
accomplish the information processing tasks of
important business functions. Examples include:
– Accounting - general ledger
– Marketing - sales analysis
– Finance - cash budgeting
– Manufacturing - material requirement planning
– Operations management - inventory control
– Human Resources mgt. - employee benefits analysis

 Scientific application programs- some broad
application categories include:
– scientific analysis
– engineering design
– monitoring of experiments
 Other application programs- applications in
– education
– entertainment
– music
– art
– medicine, etc.

Telecommunications
 Contents
– Why telecommunications is important
– Telecommunication networks
– Technical telecommunications alternatives
 Telecommunications media
 Telecommunications processors
 Telecommunications software
 Telecommunications network topologies

Why telecommunications is important
 In today’s global information society, managers, end
users, and their organizations need to electronically
exchange data and information with other end users,
customers, suppliers, and other organizations.
 Only through the use of telecommunications can
they perform their work activities, manage
organizational resources, and compete successfully
in today’s fast-changing global economy.

Why telecommunications is
important… Cont’d
 Thus, many organizations today could not
survive without interconnected networks of
computers to service the information
processing and communication needs of
their end users.

Why telecommunications is
important… Cont’d
 Telecommunications is the sending of information in
any form (e.g., voice, data, text, and images) from
one place to another using electronic or light-emitting
media.
 Data communications is a more specific term that
describes the transmitting and receiving of data over
communication links between one or more computer
systems and a variety of input/output terminals.
 Both terms are usually used interchangeably.

Telecommunication networks
 A telecommunications network model
– Before we discuss the use and management of
telecommunications, we should understand the
basic components of a telecommunications
network.
– Generally, a communications network is any
arrangement where a sender transmits a
message to a receiver over a channel consisting
of some type of medium.
– The next figure illustrates a simple conceptual
model of a telecommunications network.

Telecommunication networks
5
Telecom.
Software
End User
Terminals
Processors
Processors
Channels
& Media
1
2 2
4
3
Computers

Telecommunication networks…Cont’d
 The five basic components in a
telecommunication network include:
– Terminals
– Telecommunications processors
– Telecommunications channels and media
– Computers
– Telecommunications control software

 Terminals
– Networked microcomputer workstations or video
terminals
– Any input/output device that uses
telecommunications networks to transmit or
receive data (including telephones, office
equipment).

 Telecommunications processors, which
support data transmission and reception
between terminals and computers.
 These devices such as modems and front-
end processors, perform a variety of control
and support functions in a
telecommunications network.

 For example, they
– Convert data from digital to analog and back
– Code and decode data
– Control the accuracy and efficiency of the
communications flow between computers and
terminals in a telecommunications network.

 Telecommunications channels and media
over which data are transmitted and received
– Telecommunications channels use combinations
of media, such as copper wires, coaxial cables,
fiber optics cables, microwave systems, and
communications satellites, to interconnect the
other components of a telecommunications
network.

 Computers of all sizes and types are interconnected
by telecommunications networks so that they can
carry out their information processing assignments.
 For example,
– A mainframe computer may serve as a host
computer for a large network, assisted by a
minicomputer serving as a front-end processor
– While a microcomputer may act as a network
server for a small network of microcomputer
workstations.

 Telecommunications control software
– Consists of programs that control
telecommunications activities and manage the
functions of telecommunications networks.
– Examples include telecommunications monitors
for mainframe host computers, and network
operating systems for microcomputer network
servers.

Types of telecommunications networks
 There are many different types of
telecommunications networks. However,
from an end user’s point of view, there are
two basic types:
– Wide area networks
– Local area networks
– Metropolitan area networking

Types of telecommunications
networks…Cont’d
Wide area networks
 Telecommunications networks covering a
large geographical area are called remote
networks, long-distance networks, or, more
popularly, wide area networks (WANs).
 Networks that cover a large city or
metropolitan area (metropolitan area
networks) can also be included in this
category.

networks…Cont’d
 WANs are used by manufacturing firms,
retailers, distributors, transportation
companies, and government agencies to
transmit and receive information among their
employees, customers, suppliers, and other
organizations across cities, regions,
countries, and the world.

networks…Cont’d
Local area networks (LANs)
 Connect computers and other information
processing devices within a limited physical area,
such as an office, a building, manufacturing plant,
other work site.
 LANs have become common place in many
organizations for providing telecommunications
network capabilities that link end users in offices,
departments, and other work groups.

networks…Cont’d
 LANs allow end users in a workgroup to
communicate electronically; share hardware,
software, and data resources; and pool their efforts
when working on group projects.
 To communicate over the network, each PC in a
LAN must have a circuit board installed called a
network interface card.
 Most LANs use a powerful microcomputer having a
large hard disk capacity, called a file server or
network server.

networks…Cont’d
Internetworks
 Most LANs are eventually connected to other
LANs or wide area networks to create
internetworks.
 That is because end users need to
communicate with workstations of colleagues
on other LANs, or to access the computing
resources and databases at other company
locations or at other organizations.

networks…Cont’d
 This frequently takes the form of client/server networks,
where end user microcomputer workstations (clients) are
connected to LAN servers and interconnected to other
LANs and their servers, or to WANs and their mainframe
super servers.
 Local area networks rely on internetwork processors,
such as bridges, routers, hubs, or gateways, to make
internetworking connections to other LANs and WANs.
 The goal of such internetwork architectures is to create a
seamless “network of networks” within each organization
and between organizations that have business
relationships.

networks…Cont’d
The Internet
 Is the largest “network of networks” today, and the
closest model we have to the information superhighway
of tomorrow.
 Is a rapidly growing global web of thousands of
business, educational, and research networks
connecting millions of computers and their users in
over 100 countries to each other.
 Does not have a central computer system or
telecommunications center. Instead, each message
sent has an address code so any computer in the
network can forward it to its destination.

networks…Cont’d
 Popular Internet applications – important
telecommunications services on the Internet include:
– E-mail: exchange electronic mail with millions of Internet
users.
– Usenet: post messages on bulletin board systems formed
by thousands of special interest discussion groups.
– Internet Relay Chat: hold realtime conversations with
Internet users around the world on hundreds of discussion
channels.
– File Transfer Protocol (FTP): download data files, programs,
reports, articles, magazines, books, sounds, and other types
of files from thousands of sources to your computer system.

networks…Cont’d
– Telenet: Log on to and use thousands of internet
computer systems around the world.
– World Wide Web: point and click your way to
thousands of hyperlinked Internet sites and
resources using graphical browser software like
Internet explorer, Mosaic and Netscape.

Technical telecommunications
alternatives
 Telecommunications is a highly technical, rapidly
changing field of information systems technology.
 Most end users do not need a detailed knowledge of
its technical characteristics.
 However, it is important that you understand some of
the important characteristics of the basic
components of telecommunications networks.
 This understanding will help you participate
effectively in decision making regarding
telecommunications alternatives.

alternatives…Cont’d
1) Telecommunications Media
 Telecommunications channels are the means by
which data and other forms of communications are
transmitted between the sending and receiving
devices in a telecommunications network.
 A telecommunications channel makes use of a
variety of telecommunications media.
 These include: twisted-pair wire, coaxial cables, fiber
optic cables, terrestrial microwave, communications
satellites, cellular and LAN radio.
 Discussion of each media follows next:

Twisted-pair wire
 Ordinary telephone wire, consisting of copper wire
twisted into pairs
 These lines are used in established communications
networks throughout the world for both voice and
data transmission.
 Thus, twisted-pair wiring is used extensively in home
and office telephone systems and many local area
networks and wide area networks.

Coaxial Cable
 Consists of sturdy copper or aluminum wire wrapped with
spacers to insulate and protect it.
 The cable’s cover and insulation minimize interference and
distortion of the signals the cable carries.
 These high-quality lines can be placed underground and laid on
the floors of lakes and oceans.
 They allow high-speed data transmission and are used instead
of twisted-pair wire lines in high service metropolitan areas, for
cable TV systems, and for short-distance connection of
computers and peripheral devices.

Fiber optics
 Uses cables consisting of one or more hair-thin filaments
of glass fiber wrapped in a protective jacket.
 They can conduct light pulses generated by lasers at
transmission rates as high as 30 billion bits per second.
– This is about 60 times greater than coaxial cable and 3000
times better than twisted-pair wire lines.
 Fiber optic cables provide substantial size and weight
reductions as well as increased speed and greater
carrying capacity.
– A half-inch-diameter fiber optic cable can carry up to 50,000
channels, compared to about 5,500 channels for a standard
coaxial cable.

Terrestrial microwave
 Involves earthbound microwave systems which
transmit high-speed radio signals in a line-of-sight
path between relay stations spaced approximately
30 miles apart.
 Microwave antennas are usually placed on top of
buildings, towers, hills, mountain peaks.
 They are still a popular medium for both long-
distance and metropolitan area networks.

Communications satellites
 An important telecommunications medium is the
use of communications satellites for microwave
transmission.
 There are several dozen communication satellites
from several nations placed into stationary
geosynchronous orbits approximately 22,000 miles
above the equator.
 Satellites are powered by solar panels and can
transmit microwave signals at a rate of several
hundred million bits per second.

 They serve as relay stations for communication
signals transmitted from earth stations.
– Earth stations use dish antennas to beam microwave
signals to the satellites, which amplify and retransmit the
signals to other earth stations thousands of miles away.
 While communications satellites were used initially
for voice and video transmission, they are now also
used for high-speed transmission of large volumes of
data.

Cellular radio
 Is the radio communications technology that makes cellular
phones possible.
 It divides a metropolitan area into a honeycomb of cells. This
greatly increases the number of frequencies and users that can
take advantage of mobile phone service.
 Each cell has its own low-power transmitter, rather than having
one high-powered radio transmitter to serve the entire city. This
significantly increases the number of radio frequencies available
for mobile phone service.
 However, this technology requires a central computer and other
communications equipment to coordinate and control the
transmissions of thousands of mobile users as they drive from one
cell to another.

2) Telecommunications processors
– Telecommunications processors such as
modems, multiplexers, bridges, front-end
processors, and other devices perform a variety
of support functions between the terminals and
computers in a telecommunications network.
– Let’s take a look at some of these devices and
their functions.

Modems
 Are the most common type of communications processors.
 They convert the digital signals from a computer or
transmission terminal at one end of a communications link into
analog frequencies, which can be transmitted over ordinary
telephone lines.
 A modem at the other end of the communications line converts
the transmitted data back into digital form at a receiving
terminal.
 This process is known as modulation and demodulation, and
the word modem is a combined abbreviation of those two
words.

 Modems are used because ordinary telephone networks were
primarily designed to handle continuous analog signals
(electromagnetic frequencies), such as those generated by the
human voice over the telephone.
 Since data from computers are in digital form (voltage pulses),
devises are necessary to convert digital signals into appropriate
transmission frequencies and vice versa.
 However, digital communications networks that transmit only
digital signals and do not need analog/digital conversion are
becoming common place.

Multiplexers
 A multiplexer is a communications processor that
allows a single communications channel to carry
simultaneous data transmissions from many
terminals. Thus, a single communications line can be
shared by several terminals.
 Typically, a multiplexer merges the transmissions of
several terminals at one end of a communications
channel, while a similar unit separates the individual
transmissions at the receiving end.

Intenetwork processors
 As previously mentioned, many LANs are
interconnected by internetwork processors such as
bridges, routers, hubs, or gateways to other LANs or
WANs.
– A bridge is a communications processor that connects two
similar LANs, i.e., LANs based on the same network
standards or protocols.
– A router is a communications processor that connects
LANs to networks based on different protocols.

– A hub is a port switching communications
processor. LAN workstations, servers, printers,
and other LAN resources are connected to ports,
as are bridges and routers provided by the hub to
other LANs and WANs.
– Networks that use different communications
architectures are interconnected by using a
communications processor called a gateway.

3) Telecommunications software
 Software is a vital component of all telecommunications
networks.
 Telecommunications control software includes programs stored
in the host computer as well as programs in front-end
computers and other communications processors.
 Such software controls and supports the communications
occurring in a telecommunications network.
 For example,
– Telecommunications software packages for mainframe-based
WANs are called Telecommunications monitors
– LANs rely on software called network operating systems, such as
Novell NetWare or Microsoft LAN manager.

 Common software functions
– Access control
 establishes connections between terminals and computers
in a network. The software works with a communications
processor (such as modem) to connect and disconnect
communications links and establish communications
parameters such as transmission speed, mode, and
direction.
 May also involve automatic telephone dialing and redialing,
logging on and off with appropriate account numbers and
security codes, and automatic answering of telephone calls
from another computer.

– Transmission control
 This function allows computers and terminals
to send and receive commands, messages,
data, and programs.
 Some error checking and correction of data
transmissions may also be provided.
 Data and programs are usually transmitted in
the form of files, so this activity is frequently
called file transfer.

– Network management
 This function manages communications in a
telecommunications network. Software such as LAN
network operating systems and WAN
telecommunications monitors
– Determines transmission priorities;
– Routes (switches) messages, polls, and terminals in the
network;
– Forms waiting lines (queues) of transmission requests;
– Logs statistics of network activity and the use of network
resources by end user workstations.

– Error control
 This function involves detection and correction of
transmission errors.
 Errors are usually caused by distortions in the
communication channel such as line noise and power
surges.
– Security management
 This function protects a communication network from
unauthorized access.
 Network operating systems or other security programs
restrict access to data files and other computing resources
in LANs and other types of networks.

4) Telecommunications Network Topologies
 There are several basic types of network
topologies, or structures, in telecommunications
networks.
 The two simplest are point-to-point lines and
multidrop lines.
– When point-to-point lines are used, each terminal is
connected by its own line to a computer system.
– When multidrop lines are used, several terminals share
each data communications line to a computer.
– Obviously, point-to-point lines are more expensive than
multidrop lines.

Network Topologies
Computer
Multidrop Lines
Point-to-point Lines

 Three basic topologies are generally used in wide
area and local area telecommunications networks.
– A star network ties end user computers to a central
computer.
– In a ring network local computer processors are tied
together in a ring on a more equal basis.
– A bus network is a network in which local processors share
the same bus, or communications channel.

Network Topologies
Server
Bus Network

Network Topologies
Server
Ring
Network

Network Topologies
Star Network

Database Management
 File and database processing systems
1) File processing system - in this approach
 Data are organized, stored, and processed in
independent files of data records.
 Each file is organized to be used by a different
application program.
 Information needed may be in several different files,
each organized in a different way.

Database Management
 Management Problems of File Processing
– For many years, information systems had a file processing
orientation.
– Data needed for each application was stored in independent
data files.
– Processing consisted of using separate computer programs
that updated these independent data files.
– This approach is still being used, but it has several major
problems that limit its efficiency and effectiveness for user
applications.

Management Problems of File Processing
 Data duplication
– Independent data files include a lot of duplicated data. The
same data (such as customer's name and address) is recorded
and stored in several files.
– This data redundancy causes problems when data has to be
updated, since separate file maintenance programs have to be
developed and coordinated to ensure that each file is properly
updated.
– Of course, this proves difficult in practice, so a lot of
inconsistency occurs among data stored in separate files.
– File maintenance is a time-consuming and costly process, and
duplicated data increases the secondary storage space
requirements of computer systems.

 Lack of data integration
– Independent data files make it difficult to provide end users
with information for any ad hoc requests that require
accessing data stored in several different files.
– Special programs have to be written to retrieve data from
each independent file. This is so difficult, time-consuming,
and costly for some organizations that it is impossible to
provide end users or management with such information.
– If necessary, end users have to manually extract each
separate application and prepare customized reports for
management.

 Data dependence
– In file processing systems, there is a significant dependency
between the organization of files, their physical locations on
storage hardware and the application software used to
access those files.
– Data dependence refers to the close relationship between
data stored in files and the specific software programs
required to update and maintain those files.
– Every computer program must describe the location of the
data it uses. In a traditional file environment, any change to
the format or structure of data in a file necessitates change
in all of the software programs that use these data.

 Data confusion
– refers to inconsistencies among various
representations of the same piece of data in
different information systems and files.
– Overtime, as different groups in a firm update
their applications according to their own
business rules, data in one system becomes
inconsistent with the same data in another
system.

 Excessive software costs result from creating,
documenting, and keeping track of so many files
and different applications many of which contain
redundant data.
– Organizations must devote large part of their
information systems resources merely to
maintaining data in hundreds and thousands of
files.
– New requests for information can only be satisfied
if programmers write new software to strip data
from existing files and recombine them into new
files.

Database Management
2) The Database Management Solution
– Many of the problems of the traditional file environment
can be solved by taking a database approach to data
management and storage.
– A database is an integrated collection of logically related
records and files. It consolidates records previously stored
in independent files so that it serves as a common pool
of data to be accessed by many different application
programs.
– The data stored in a database is independent of the
computer programs using it and of the type of secondary
storage devices on which it is stored.

The Database Management Solution
 Database Management involves the control
of how databases are created, interrogated,
and maintained to provide information
needed by end users and the organization.
– The traditional approach to organizing data
(Figure).
– How a Database Management system helps a
business organize data (Figure).

The Database Management Solution
 Components of a Database Management system
– Special software called a database management system
(DBMS) permits data to be stored in one place while making
them available to different applications.
– DBMS serves as an interface between the common
database and various application programs.
– Database management software has three components:

Components of a Database Management
system
 Data Definition Language (DDL) -defines each data
element as it appears in the database before it is
translated into the form required by various
application programs.
– Database programming specialists use this language when
they are developing the database.
 Data Manipulation Language (DML)- is a special tool
for manipulating data in the database. It has
features that can be utilized by both business and
technical specialists for satisfying information
requests and for application development.

system
 The most prominent data manipulation
language today is SQL, or Structured Query
Language, which is the data manipulation
language for mainframe DBMSs.
Select xxx (columns)
From xxx (tables)
Where xxx = "xxx" (condition)

system
 Data dictionary - is an automated file that stores
definitions of data elements and other characteristics
such as usage patterns, ownership (who in the
organization is responsible for maintaining the data),
relationships among data elements, and security.
 In other words, it is a computer-based catalog or
directory containing metadata, that is, data about
data.

Database Management
 Technical foundations of database management
– In all information systems, data resources must be
organized and structured in some logical manner so that
they can be accessed easily, processed efficiently, retrieved
quickly, and, managed effectively.
– Thus, data structures and access methods ranging from
simple to complex have been devised to efficiently organize
and access data stored by information systems.
– A discussion of these concepts follows:

Technical foundations of database
management
a) Logical Data Elements
– In information systems, data are organized in a
hierarchy that starts with bits and bytes and
progresses to fields, records, files, and
databases.

Logical Data Elements
Database
File
Record
Field
Byte
Bit
Human Resources Database
personnel file
payroll file
Asrat Belachew 36 220 Kebeke 03
Bekelech Tesfay 24 63 Kebele 04
Belay Zeru 55 22 Kebele 18
Asrat Belachew 36 220 Kebele 03
Asrat Belachew (Name field)
1011 1010 (letter Z in ASCII)
1, 0
Data Hierarchy Example

Technical foundations of database
management
b) Database Structures
– The way data are organized in a database
depends on the nature of the problems they are
required to solve. There are three principal
logical database structures:
 the hierarchical
 the network, and
 the relational
– Each model is best suited to solving a particular
class of problems.

Database Structures
 The Hierarchical structure
– This model organizes data in a top-down, treelike
manner.
– Each record is broken down into pieces of records
called segments.
– The database looks like an organization chart with
one root segment and any number of subordinate
segments.

Database Structures…Cont’d
 The segments, in turn, are arranged into multilevel
structures, with an upper segment linked to a
subordinate segment in a parent-child relationship.
– A "parent" segment can have more than one "child" but a
subordinate "child" segment can have only one "parent".
 Thus, all the relationships among records are one-to-
many since each data element is related only to one
element above it.
 Data is accessed by starting at the root and moving
progressively downward along the branches of the
tree until the desired record is located.

Hierarchical Structure
Department
Project A Project B Project C
Employee 1 Employee2

 The Network structure
– This structure is best at representing many-to-many
relationships among records- that is, the network model
allows entry into a database at multiple points, because any
data element or record can be related to any number of
other data elements.
– For example, departmental records can be related to more
than one employee record, and employee records can be
related to more than one project record.
– In other words, a "child" can have more than one "parent".

Network Structure
Department
A
Department
B
Employee 2
Employee 1 Employee 3
Project A Project B

 The Relational Structure
– The most recent database structure, the relational database
model, was developed to overcome the limitations of the
other two models in representing data relationships.
– The relational model represents all data in the database in
simple two-dimensional tables called relations.
– A data element in any one table can be related to any piece
of data in another table as long as both tables share a
common data element.
– It does not rely on a parent-child relationship. Instead, it
groups all data into tables from which the actual data
relationships can be built.

Relational Structure
Deptno Dname Dloc Dmgr
Dept A
Dept B
Dept C
Empno Ena
me
Etitle Esal
ary
Deptno
Emp 1 Dept A
Emp 2 Dept A
Emp 3 Dept B
Emp 4 Dept B
Emp 5 Dept C
Emp 6 Dept B
Employee Table
Department Table

Information Systems Technology Chapter Three

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