INTRODUCTION
INTRODUCTION
TO UNDERSTANDING
COMPUTERS:
This module includes
the following lessons:
Lesson 1: An
Introduction to Computer Technology
Lesson 2: Computing
Environments
Lesson 3: Computer
Applications
Lesson 4: What to Do
Next?
AIMS
AND OUTCOMES
This module has six
primary aims. These are to:
1. Introduce
the key components of a computer system (hardware, software, data)
2. Acquaint
readers with how computers work
3. Present
the basic concepts of various computing environments
4. Give
a broad view of how technology is improving communications through the use of electronic
mail and the Internet.
5. Discuss
the various kinds of storage media and recording formats and methods commonly
associated with a computer
6. Explain
how to obtain more information on computerisation.
At the end of this
module, you should understand
1. The
key components of a computer system (hardware, software, data)
2. The
basics of how computers work
3. The
basic concepts of various computing environments
4. How
technology is improving communications
5. The
various kinds of storage media and recording formats and methods available
6. Where
to go for more information on computerisation.
LESSON
1
AN INTRODUCTION
TO COMPUTER
TECHNOLOGY
This lesson
introduces key concepts related to how computers work. Computer related
terms are defined and
basic computer functions are explained. In particular,
the following topics
are addressed.
• What
is a computer?
• What
are the components of a computer?
• How
does a computer work?
• How
does the software work?
• How
does a computer process information?
• How
does the computer’s memory work?
• How
is data stored?
• Why
is documentation important?
• What
are viruses?
Please remember, this
introductory lesson is not intended to provide a comprehensive explanation of
the technical details of computerisation. Information is provided in
order to introduce
you to key computer concepts and provide an overview of
computerisation. The
average computer user, as opposed to those pursuing a career in computing, do not
need to know more than the information provided here in order to work
effectively with information technologies.
WHAT
IS A COMPUTER?
A computer allows
users to store and process information quickly and automatically.
A computer is a
programmable machine. It allows the user to store all sorts of
information and then
‘process’ that information, or data, or carry out actions with the
information, such as
calculating numbers or organising words.
Computer: A machine that can
receive and store information and change or process it.
Information: Knowledge that is
communicated.
Data (pl.): The representation of
information in a formalised manner suitable for communication,
interpretation and processing, generally
by a computer system. Note: the term ‘raw data’ refers to
unprocessed information. Computers
can be generally classified by size and power, although there can be considerable
overlap. Following are descriptions of several different types of
computers.
Mainframe
computers are large-sized, powerful multi-user computers that can
support concurrent
programs. That means, they can perform different actions or
‘processes’ at the
same time. Mainframe computers can be used by as many as
hundreds or thousands
of users at the same time. Large organisations may use a
mainframe computer to
execute large-scale processes such as processing the
organisation’s
payroll.
Mini-computers
are mid-sized multi-processing computers. Again, they can perform
several actions at
the same time and can support from 4 to 200 users simultaneously.
In recent years the
distinction between mini-computers and small mainframes has
become blurred. Often
the distinction depends upon how the manufacturer wants to
market its machines.
Organisations may use a mini-computer for such tasks as
managing the
information in a small financial system or maintaining a small database
of information about
registrations or applications.
Workstations
are powerful, single-user computers. They have the capacity to
store
and process large
quantities of data, but they are only used by one person at a time.
However, workstations
are typically linked together to form a computer network
called a local area
network, which means that several people, such as staff in an office,
can communicate with
each other and share electronic files and data.
Computer network: A grouping of
computers and peripherals connected together by telecommunications links to
enable a group of users to share and exchange
information. A workstation is similar to
a personal computer but is more powerful and often comes with a higher-quality
monitor. In terms of computing power, workstations lie in
between personal
computers and mini-computers. Workstations commonly support
applications that
require relatively high-quality graphics capabilities and a lot of
memory, such as
desktop publishing, software development and engineering
applications.
Personal
computers (PCs), also called microcomputers, are the most popular type of
computer in use
today. The PC is a small-sized, relatively inexpensive computer
designed for an
individual user. Today, the world of PCs is basically divided between
IBM-compatible and
Macintosh-compatible machines, named after the two computer
manufacturers.
Computers may be called ‘desktop’ computers, which stay on the
desk, or ‘laptop’
computers, which are lightweight and portable. Organisations and
individuals use PCs
for a wide range of tasks, including word processing, accounting,
desktop publishing,
preparation and delivery of presentations, organisation of
spreadsheets and
database management. Entry-level PCs are much more powerful
than a few years ago,
and today there is little distinction between PCs and
workstations.
WHAT
ARE THE COMPONENTS OF A COMPUTER?
Computers are made up
of two parts: the hardware and the software.
Hardware: The physical
equipment required to create, use, manipulate and store electronic data.
Software: The computerised
instructions that operate a computer, manipulate the data and execute
particular functions or tasks.
All computers require
the following hardware components:
Central processing
unit (CPU): The chip or chips at the heart of a computer that enable it to
process data. Also known as a processor.
Memory: An area within a
computer system that holds data waiting to be processed.
Storage device: The place where a
computer puts data.
Input devices : The
devices that allow data and instructions to enter a computer
(such as a keyboard,
mouse, scanner)
Input: Any resource required
for the functioning of a process, in the course of which it will be transformed
into one or more outputs.
Output devices: the
devices that allow information to be represented (that is, given out) to the
user, such as a display screen or printer)
Output: The product of the
transformation of inputs by a process. Printers, scanners and
external disk drives that may be connected to the computer are also sometimes
called ‘peripheral devices’.
Peripheral device: Any piece of
equipment in a computer system that is not actually inside the
computer itself. The
central processing unit (CPU) is the heart of the computer. It carries out all
of the instructions given in a program, such as a word processing or spreadsheet
program.
The CPU consists of
one or more chips (another name for “integrated circuits”).
Chip: A small piece of
semi-conducting material (such as silicon) about 1 centimetre (¼ inch) square
on which an integrated circuit is embedded. An integrated circuit is a number
of electronic components joined together to form a path for electricity.
Central processing unit
chips contain the circuits representing
the CPU. A microprocessor is a particular type of chip. The original IBM
personal computer used the Intel 8088 microprocessor. Most of today’s
microcomputers are designed around a microprocessor from one of two product
families: x86 or Power. The 80286, 80386, and 80486 models that followed were
referred to by the last three digits, 286, 386, and 486. For the next
generation, however, Intel broke with tradition and introduced the Pentium in
1993. In 1997, it introduced the Pentium II to address
multi-media
applications, and most recently the Pentium III to address the new
opportunities
provided by access to large volumes of information on the world wide
Web. Other
manufacturers of chips (such as Cyrix) produce chips of similar power
and capabilities. CPU’s
are not all equal. Some process data faster than others. A computer contains a system
clock that emits pulses to establish the timing of all systems operations. The system
clock operates at a speed quite different from a clock that keeps track of the
time of the day. The
system clock determines the speed at which the computer can
execute an
instruction, and therefore limits the number of instructions the computer
can complete within a
specific amount of time. The time to complete an instruction
execution cycle is
measured in megahertz (MHz) or millions of cycles per second.
Although some
instructions require multiple cycles to complete, the processor speed
should be thought of
in terms of the number of instructions the processor can execute
in one second. Today,
microprocessor speeds exceed 300 MHz. If all other
specifications are
identical, then higher megahertz ratings means faster processing.
When determining what
type of computer you are using or considering what type of
computer to acquire,
it is important to know that these terms – 286, 386, 486, Pentium
– refer to the type
of processor in the computer. Newer computers will come with
Pentium
microprocessors (or the equivalent from other manufacturers); older ones
with microprocessors
from the x86 family. It is important to know the type of processor in your
computer. Some newer computer programs will not run on older processors, and
some newer processors are too sophisticated for older software. The faster the
processor in a computer, the more quickly the computer will perform operations.
The most common type of memory that most users are familiar with
is ‘main memory’ or ‘RAM’ (random-access memory).
Random access memory
(RAM): An area in the computer system unit that temporarily holds a
user’s
data, operating system instructions and
program instructions. The word ‘main’ is used to distinguish it from external mass
storage devices such as the hard drive or disk drives. Note that the term ‘mass
storage’ refers to various techniques and devices for storing large amounts of
data; mass storage is distinct from memory because it retains data even when
the computer is turned off. Thus mass storage is sometimes referred to as
‘auxiliary storage’.
Following are
definitions of common storage devices:
1.
Storage: The area within a computer system where data can be left on a
longer term basis while it is not needed for processing.
2.
Diskette. A small, removable, flexible plastic disk covered with a thin
layer of a magnetisable substance, onto which digital data can be recorded and stored.
Also known as a floppy disk.
3.
Hard drive: The storage area within the computer itself, where megabytes of
space are available to store bits of information. Also known as a hard disk.
4.
Optical disk: A storage device that uses reflecting surfaces and laser
technology to read and write data on a disk. Also known as a laser disk.
5.
Magnetic tape: A continuous plastic strip covered with magnetic oxide; the tape
is divided into parallel tracks onto which data may be recorded by selectively magnetising
parts of the surface, or spots, in each of the tracks. The data can then be
stored and reused.
HOW DOES
A COMPUTER WORK?
A computer functions
in the following manner:
• The
computer accepts input. Computer input is whatever is entered or
fed into a
computer system.
Input can be supplied by a person (such as by using a keyboard)
or by another computer
or device (such as a diskette or CD-ROM). Some
examples of input
include the words and symbols in a document, numbers for a
calculation,
instructions for completing a process, pictures, and so on.
• The
computer performs useful operations, manipulating the data in
many ways.
This manipulation is
called processing. Examples of processing include
performing
calculations, sorting lists of words or numbers, modifying documents
and pictures
according to user instructions, and drawing graphs. A computer
processes data in the
CPU.
Process: A systematic series
of actions a computer uses
to manipulate data.
• The
computer stores data. A computer must store data so that it is
available for
processing. Most
computers have more than one location for storing data (the
hard drive or C:\,
and the floppy drive or A:\). The place where the computer
stores the data depends
on how the data is being used. The computer puts the data
in one place while it
is waiting to be processed and another place when it is not
needed for immediate
processing. The storage of data in the computer is called
‘online storage’
while the storage of data on computer tapes, diskettes or
CD-ROMs is called
‘offline storage’.
• The
computer produces output. Computer output is information that has
been
produced by a
computer. Some examples of computer output include reports,
documents, music,
graphs, and pictures. Output can be in several different
formats, such as
paper, diskette, or on screen.
A computer receives
data as input, processes it, stores it and
then produces output.
HOW DOES
THE SOFTWARE WORK?
Software is the
computerised instructions that operate the computer, execute particular
functions or tasks,
and manipulate the data. For software (the instructions) to perform
various functions, it
must be programmed. That is, the instructions need to be written
in a programming
language that the computer can understand. Without a program, a
computer is useless.
Programming language:
An
artificial set of rules, vocabulary and syntax used to instruct the computer to
execute certain tasks.
Computer program: A sequence of
instructions that can be executed by a computer to carry out a process. Over
the years, a wide range of programming languages have been developed,
including BASIC,
FORTRAN, PASCAL, C++, JAVA, and so on. Each language has
a unique set of words
(codes) that it understands and a special syntax for organising
program instructions.
The language the computer actually understands is called machine language,
which comprises numbers only. This language is used by the computer to
understand the programming language and translate the terms into executable
instructions. Lying between programming languages and machine languages are
assembly languages.
Assembly languages
have the same structure and set of commands as machine
languages but they
enable a program to use names instead of numbers.
Please note: most
people who use computers today do not need to worry about
programming, machine,
or assembly languages. This is because the software being
used today is written
in a highly user-friendly manner and in a way that does not
require knowledge of
the computer languages which were used to create and use it.
User friendly: Computer software or
hardware that is simple to set up, run and use.
There are two kinds
of software, systems software and applications software.
Systems
software includes the operating system and all the utilities that enable
the
computer to function.
The most important program that runs on a computer is the
operating system.
Every general-purpose computer must have an operating system in
order to run other
programs. This includes controlling functions such as the
coordination of the
hardware and applications software, allocating storage facilities,
controlling the input
and output devices and managing time sharing for linked or
networked computers.
In many respects an operating system works like an air traffic
controller to
coordinate activities within the computer. Examples of operating
systems are Windows
NT, DOS and OS/2. The Windows family of operating systems
includes a Graphical
User Interface (GUI) that makes the software user friendly.
Operating system: A collection of
software that allows a computer to function.
Applications
software includes programs that users access to carry out work. They
include applications
for the following functions.
• Word processing is
the most common applications software. The great advantage
of word processing
over using a typewriter is that you can make changes without
retyping the entire
document. Word processors make it easy to manipulate and
format documents.
• Spreadsheets are
computer programs that let people electronically create and
manipulate
spreadsheets (tables of values arranged in rows and columns with
predefined
relationships to each other). Spreadsheets are used for mathematical
calculations such as accounts,
budgets, statistics and so on.
• Database management
applications are computer programs that let people create
and manipulate data
in a database. A database is a collection of related
information that can
be manipulated and used to sort information, conduct
statistical analyses
or generate reports.
• Presentation
packages and graphics are computer programs that enable users to
create highly
stylised images for slide presentations and reports. They can also be
used to produce
various types of charts and graphs. Many software applications
include graphics
components including: paint programs, desktop publishing
applications and so
on.
• Communications
applications typically include software to enable people to send
faxes and emails and
dial into other computers. Software programs are continually being written or upgraded to
undertake certain tasks. As a result the software
can become obsolete
quickly. Software can be either ‘proprietary’ (also called ‘closed’) or
‘open’. Proprietary software is privately owned and controlled. A proprietary
software design or technique is one that is owned by a company, which will
usually not divulge specifications that would allow other companies to
duplicate the product. Increasingly, proprietary software is seen as a
disadvantage in many organisations; users prefer to use ‘open’ software, which
is software designed using specifications that are publicly accessible. The
great advantage of open software is that anyone can create add-on products for
it because they can understand how it was designed. People using open software
can mix and match products from different manufacturers. By making software
public, however, a manufacturer allows others to duplicate its product, which
many manufacturers do not want.
HOW DOES
A COMPUTER PROCESS
INFORMATION?
When data is input
into a computer, the numbers or words we understand are
translated into a
binary numbers system. Binary is the language of computers.
Everything you type,
input, output, send, retrieve, draw and so on is, in the end,
converted to the
computer’s native language: binary.
Binary number system:
A
numerical system wherein each digit stands for a power of two. The binary
system uses only two symbols, 0 and 1,
to represent values.
In the decimal
system, commonly used in most countries, each digit represents a value
of 10. For example,
the number 103 would break down as follows:
1 x 100 = 100
0 x 10 = 0
3 x 1 = 3
103 = 103
In the binary system,
each digit position represents a value of 2. Because computers
use the binary
system, powers of 2 play an important role. This is why everything in
computers seems to
come in 8s (2 to the 3rd power), 64s (2 to the 6th power),
128s (2
to the 7th power),
and 256s (2 to the 8th power). Therefore, in the binary system, the
number 103 would
break down as follows:
1 x 64 = 64
1 x 32 = 32
0 x 16 = 0
0 x 8 = 0
1 x 4 = 4
1 x 2 = 2
1 x 1 = 1
1100111 = 103
The values in a
binary system -- the 0s and 1s -- are called ‘binary digits’ or bits.
Binary digit (bit): A digit within the binary
number system. A bit is the smallest unit of information held in a computer. The
computer’s electronic circuits have only two states, on or off, and therefore
can only understand 0s and 1s, which may represent such opposites as on or off,
yes or no, or up or down. This is why all computers use the binary system. In
order to make the
bits useful, they are
combined into ‘bytes’ of information.
Byte: A combination of bits
that represent one character. A byte is usually composed of 8 bits.
Computer programmers
have developed codes for various bytes of information, so
that they may be read
by different computer programs. For example, one code might
define the letter A
as ‘11000001’ and the letter B as 11000010’. The number 6 might
be defined as
‘11110110’ and the number 8 as ‘11111000’. When the person entering
data strikes the A
key on the keyboard, the computer registers it as ‘11000001’. When
he or she enters the
B, the computer reads it as ‘11000010’. Similarly, the number 6
is understood by the
computer as ‘11110110’ and the number 8 as ‘1111100’. In this
way, the computer can
store words and numbers as binary digits and then retrieve
them and convert them
back into words or numbers as required.
As discussed earlier,
this work of manipulating, storing and processing the data takes
place in the Central
Processing Unit, the computer’s main memory. The CPU consists
of an arithmetic and
logic unit, or ALU, a control unit, and a set of registers.
• The
arithmetic and logic unit is the portion of the CPU where arithmetic and
logical operations
take place.
• The
control unit is the part of the CPU that supervises the general operations of
the computer.
• The
registers are devices that hold data inside the computer’s memory long
enough to execute a
particular function, such as indexing, calculating, sorting or
otherwise
manipulating data. They are the CPU’s own internal memory. Data travels from
one part of the computer to another through a kind of path known as a bus.
Bus: The channel or path
that lets the parts of a computer communicate with each other.
Similar to a school
bus for school children, a computer data bus picks up a load of
data from one of the
components on the main computer board and then transfers the
data to another
component on the main computer board. The main circuit board of a
microcomputer is also
known as the motherboard. The motherboard is the principal
board that has
connectors for attaching devices to the bus. Typically, it contains the
CPU, memory and basic
controllers for the system. The data bus is really a series of
electrical circuits
that connect the various electrical elements on the main board.
The data are input
into the computer and processed in the CPU. They travel along the
bus to be stored in
the computer’s memory. The amount of memory available is
described in bytes of
information, referring to the combination of bits representing
characters. The
higher the number of bytes the more memory the computer has.
Today’s computers
hold ‘megabytes’ or even ‘gigabytes’ of data. A megabyte is a
unit of one million
bytes; a gigabyte is one billion bytes, and a terabyte is one trillion
bytes. If a computer
has a memory of 64 megabytes, then it can hold 64 million bytes
of information.
Data can be stored so
that it is readable again only using the software with which it
was created, or it
can be stored in other formats, so that it may be transferred or used
by other software
programs. There is a standard character code used to store data so
that it may be used
by other software programs; this code is called ASCII or American
Standard Code for
Information Interchange. The ASCII code assigns a specific
pattern of bits to
each character, as described above. Another code that may be found,
especially in
IBM-brand mainframe computers, is EBCDIC, or Extended Binary
Coded Decimal
Interchange Code. The important point to remember about these
codes is that their
main value is to store information so that it is readable by other
computers. By using
ASCII or EBCDIC, it is possible for people to retrieve and use
someone else’s data
using a different type of hardware or software. The main
disadvantage of using
ASCII or EBCDIC is that the formatting or other special
qualities of
computerised information may be lost.
WHAT
IS COMPUTER MEMORY?
As defined earlier,
memory refers to the temporary internal storage areas within a
computer. The term
memory is usually used as shorthand for ‘physical memory’,
which refers to the
actual chips capable of holding data. Some computers also use
‘virtual memory’,
which expands physical memory onto a hard drive.
The main type of
memory and the most familiar to users is random access memory
(RAM). RAM is the
same as main memory. A computer can both write data into
RAM and read data
from RAM.
Every time a user
turns on his or her computer, a set of operating instructions is
copied from the hard
disk into RAM. These instructions, which help control basic
computer functions,
remain in RAM until the computer is turned off. Most RAM is
volatile, which means
that it requires a steady flow of electricity to maintain its
contents. As soon as
the power is turned off, whatever data was in RAM disappears.
The contents of RAM
are necessary for the computer to process data. The results of
the processing are
kept temporarily in RAM until they are needed again or until they
are saved onto the
hard disk or other storage device.
Today the storage
capacity of RAM is measured in megabytes (MB). PCs
(microcomputers)
typically have between 16 and 64 MB of RAM, which means they
can hold between 16
and 64 million bytes of data (a standard A4 page of text typically
holds about 2,000
bytes or characters of text).
Other types of memory
include
• ROM
(read only memory): unlike RAM, ROM is non-volatile and only permits
the user to read
data. Computers almost always contain a small amount of
read-only memory that
holds instructions for starting up the computer.
• PROM
(programmable read-only memory): a PROM is a memory chip on which
you can store a
program. Once the PROM has been used, you cannot wipe it clean
and use it to store
something else. Like ROMs, PROMs are non-volatile.
• EPROM
(erasable programmable read-only memory): an EPROM is a special type
of PROM that can be
erased by exposing it to ultraviolet light.
• EEPROM
(electrically erasable programmable read-only memory): an EEPROM
is a special type of
PROM that can be erased by exposing it to an electrical charge.
HOW ARE DATA STORED?
It is very important
to distinguish between memory, which refers to the circuitry that
has a direct link to
the computer processor, and the storage, which refers to media
such as disks that
are not directly linked to the processor. Remember, a storage device
is anything that is
used to store computer data. Floppy disks, hard disks, optical disks,
CDs and magnetic
tapes are all types of storage device.
Physical storage
refers to how data are actually kept on the storage disk. The most
commonly used medium
for storage is magnetic storage. With magnetic storage the
computer stores data
on disks and tape by magnetising selected particles of an
oxide-based surface
coating. The particles retain their magnetic orientation until that
orientation is
changed. Thus magnetic disks and tapes are modifiable storage media.
The two most popular
types of magnetic storage media are hard disks and diskettes.
Magnetic tape
provides a third type of magnetic storage, and optical disk is a new
storage medium.
Following is a discussion of each; the definitions included earlier
are repeated.
Hard drive or hard
disk storage provides faster access to files than a diskette.
Hard drive: The storage area
within the computer
itself, where megabytes of space are
available to store
bits of information. Also known as a
hard disk.
A hard disk platter
is a flat, rigid disk made of aluminium or glass and coated with a
magnetic oxide. A
hard disk consists of one or more platters and their read-write
heads. A read-write
head is the device that reads the data from the disk platter into the
computer. It also
records (or ‘writes’) data onto the platters. Hard disk platters in microcomputers
are typically 3½ inches (about 10 centimetres) in diameter: the same
size as the circular
disk in a diskette. However, the storage capacity of a hard
disk far exceeds that
of a floppy disk. Also, the access time of a hard disk is
significantly faster
than a diskette. Unlike diskettes, which begin to rotate when one
requests data, hard
disks are continually in motion, so there is no delay as the disk
spins up to speed.
Like diskettes, hard disks provide random access to files by
positioning the
read-write head over the sector that contains the requested data.
Diskette. A small, removable,
flexible mylar plastic disk covered with a thin layer of a magnetisable
substance, onto which digital data can
be recorded and stored. Also known as a floppy disk.
Diskettes get another
name – floppy disk – from the thin mylar disk. If one cuts open
the disk casing (not
recommended because the disk will be ruined) one would see that
the mylar disk inside
is thin and “floppy”. Diskettes are also called floppies.
Although today’s
microcomputers typically use 3½ inch (about 10 centimetre) disks,
you may still find 5¼
inch (about 15 centimetre) disks that were popular many years
ago. Finding a disk
drive to read 5¼ inch disks may be very difficult.
Diskettes are
generally used for transporting or shipping data files or for making
duplicate copies of
data files for back-up purposes. The storage capacity of a diskette
varies but is
considerably smaller than that of a hard drive.
Since the 1960s,
magnetic tape has been a popular form of mainframe computer
storage.
Magnetic tape: A continuous plastic
strip covered with magnetic oxide; the tape is divided into parallel tracks onto
which data may be recorded by selectively magnetising parts of the surface, or
spots, in each of the tracks. The data can then be stored and reused.
When IBM introduced
its first microcomputer in 1981, the legacy of tape storage
continued in the form
of a cassette tape drive, similar to those used for audio
recording and
playback. Using tape as a primary storage device, however, instead of a
hard disk is slow and
inconvenient because tape requires sequential access rather than
random access.
Sequential access
means that data is stored and read as a sequence of bytes along the
length of the tape.
To find a file stored on a microcomputer tape storage device, one
has to advance the
tape to the appropriate location of the file, then wait for the
computer to slowly
read each byte until it finds the beginning of the file. Like an
audio cassette, for
example, a user must go through the tape in sequence to find the
part he or she wants.
Microcomputer users
quickly abandoned tape storage for the convenience and speed
of random access disk
drives. Recently, however, tape storage for microcomputers
has experienced a
revival, not as a principal storage device but for making backup
copies of the data
stored on hard disks. The data on magnetic storage can be easily
destroyed, erased, or
otherwise lost. Protecting the data on the hard disk is of
particular concern to
users because it contains so much data, which could be difficult
and time consuming to
reconstruct. This is why backups are so important.
Back up: To copy a computer
file or collection of files to a second medium, usually on a diskette or
magnetic tape, so that the data are safe in case the original file is damaged
or lost. Backups are usually copied to storage devices that can be removed from
the computer and kept separately from the original.
A tape backup is a
copy of the data from a hard disk, stored on magnetic tape and used
to recover lost data.
A tape backup is relatively inexpensive and can rescue an organisation from the
overwhelming task of trying to reconstruct lost data. Backing up electronic
data is critical to protecting it from loss or damage.
The most popular
types of tape drives for microcomputers also use tape cartridges, but
there are several
tape specifications and cartridge sizes. A tape cartridge is a
removable magnetic
tape module similar to a sound or video cassette tape. Quarter
inch tape, called
QIC, is a tape cartridge that contains ¼ inch (approximately ½
centimetre) wide
tape. Depending on tape length, QIC tape capacities range from 340
MB to 2 gigabytes.
Digital audio tape, called DAT, was originally an audio recording
format, but is now
also used for data storage. The 4mm wide DAT tape format
storage capacity
ranges from 2 gigabytes to 12 gigabytes.
In addition to
magnetic storage, there is also optical storage.
Optical disk: A storage device that
uses reflecting surfaces and laser technology to read and write data on a disk.
Also known as a laser disk. With optical storage, data is burned
into the storage medium using beams of laser light. The burns form patterns of
small pits in the disk surface to represent data. The pits on optical media are
permanent, so the data cannot be changed. Optical media are very durable, but
they do not provide the flexibility of magnetic media for changing the data
once they are stored.
There are three types
of optical disks.
• CD-ROM’s
are the most popular type of optical storage. CD-ROM stands for
Compact Disc Read
Only Memory. A computer CD-ROM disk, like its audio
counterpart, contains
data that has been stamped on the disk surface as a series of
pits. To read the
data on a CD-ROM an optical read head distinguishes the
patterns of pits that
represent bytes. CD-ROM disks provide tremendous storage
capacity. CD-ROMs
usually come with data already written onto them. These
days most
applications software is provided on CD-ROM.
• It
is now possible for computer users to write data to an optical disk. These are
known as WORM disks,
which stands for ‘Write Once Read Many’. A single CD
holds up to 680
megabytes, equivalent to over 300,000 pages of text in character
format, and these
disks are quite durable. These CDs are know as CD
re-recordable (CD-R).
There are other types of WORM disks, although there is no
standard for these.
• There
is a third type of optical disk which can be erased and use to rewrite new
information. These
are sometimes known as EO (erasable optical) disks and
CD-RW (CD
rewritable).
Magneto-optical disks
combine magnetic disk and CD-ROM technologies. Like
magnetic media they
can read and written to and like floppy disks they are removable.
They can store over 200
MB of data, and speed of access to this data is faster than a
floppy but slower
than a hard drive. There is no universal standard for these yet.
CD-ROMs and
magnet-optical disks are very useful for storing images. These take up
much more storage
space than data in character format, such as in word-processed
files.
THE IMPORTANCE
OF DOCUMENTATION
The computer
hardware, software and peripherals will be accompanied by
documentation, which
explains how the various systems or programs operate.
Documentation: Information needed to
develop, use or maintain computer hardware and software and to permit access
and retrieval of the data. Although documentation usually comes in
the form of printed manuals, guide books, it may also come in electronic form,
such as in ‘help screens’ contained within the computer software or
documentation in data dictionaries and so on. Often, documentation is created
when a specific computer application is used. For example,
if a government
office creates a data base of employees in order to administer payroll,
documentation may be
created describing how the database was established, what it is
to be used for and
what data fields have been created. This documentation can be
critical to
understanding the database system, particularly if it is being managed in an
archival environment
long after the creators of the system have left. Documentation should
always be retained. Disposing of documentation can cause problems in the future,
particularly if you have to reload software from the beginning. Documentation
can also contain licences for the legitimate use of the software. Therefore it
is critical to protect documentation and
ensure it is readily
available.
PROTECTING
AGAINST VIRUSES
Virus: A computer program
that is planted in one computer and then transferred, hidden in useful
information, to one or more other
computers with the intention of corrupting or wiping out information in the recipient
computer.
Viruses are extremely
common. Many different types of viruses exist, ranging from
ones that prevent you
from opening up word-processed documents through to ones
that destroy the
entire contents of a hard drive. Viruses can be caught in several ways,
for example by
exchanging floppy disks, via electronic mail messages and through
downloading documents
from the Web. Networks make it much easier for viruses to
move around. Once a
virus gets into an organisation’s computer system it can spread
very quickly. New
viruses appear each week, so it is essential that users have up-todate
anti-virus software
to combat this problem.
If users have
software that is unlicenced it could mean that it is ‘pirate’ or ‘bootleg’
software. This is
software that has been illegally copied. Software of this nature
sometimes contains
viruses that can be extremely damaging to computers.
SUMMARY
This lesson
introduced basic information about how computers work, including
information about
• the
components of a computer
• how
a computer works
• how
software works
• how the
computer’s memory works
• how
data is stored.
STUDY
QUESTIONS
1. In your own words,
explain what a computer is.
2. Describe four
different types of computers.
3. Briefly explain
how a computer works.
4. What is hardware?
5. What is software?
6. What is the
central processing unit of a computer? Why is it so important to the
operation of the
computer?
7. Describe at least
four different applications, or uses, of computers.
8. What is a binary
number system?
9. What is a bit?
10. What is a byte?
11. What is the
meaning of computer ‘memory’?
12. What is RAM?
13. What is a storage
device?
14. What is a
diskette?
15. What is a hard
drive?
16. What is a
database?
17. What are the key
differences between a diskette and a hard drive?
18. What is magnetic
tape and how is it different from a hard drive?
19. Explain the
concept of backing up files.
20. What is an
optical disk?
21. What is
documentation and why is it so important?
22. How can viruses
damage computers?
LESSON
2
COMPUTING
ENVIRONMENTS
This lesson examines
three computer environments: mainframe computing, networks
(such as Intranets),
and the Internet. It introduces key concepts related to how
mainframes, networks
and the Internet work.
Please remember, this
lesson is not intended to provide a comprehensive explanation
of the technical
details of mainframe computing, networks and the Internet.
Information is
provided in order to introduce you to key concepts and provide an
overview of these
computing environments.
MAINFRAME
COMPUTING
Mainframe computing
developed at a time when computational power was an
expensive and scarce
resource. In order to use the expensive computer technologies
efficiently,
organisations had to share their resources. Many of computerised
applications, such as
invoicing, purchasing, payroll, accounting and so on, involved
the organisation as a
whole.
If the original
reasons for the mainframe computing model were cost and scarcity of
resources, the
current reasons for sharing computer power are
• security: the
protection of data from outside or unauthorised access
• integrity: the
guarantee that the data is not corrupted and that repeatability is
achievable using the
same applications and data
• system availability:
centralised facilities can be operated by teams in shifts
24 hours a day,
maximising the investment in IT equipment and allowing large
data processing
activities to be carried out efficiently
• data sharing:
data input or created in one part of the organisation becomes
available to other
parts
• applications:
many modern applications, such as personnel management systems,
require access to a
shared pool of resources.
Today, mainframe
computing is no longer an expensive resource; sharing is still a
cost-effective means
of providing computational power. Recent studies have shown
that on a per-user
basis, mainframe computing provides the least expensive form of
computing.
A mainframe
environment involves not just the hardware. The security, integrity and
availability of the
mainframe system can only be achieved if the computer centre is
staffed by people
with the necessary skills, operated according to a set of practices and
managed with the
discipline (that is, the processes and procedures) that ensures the
appropriate levels of
security, integrity and availability. This is the ‘mainframe
environment’. In a mainframe
environment, many people share access to a
mainframe computer.
A large central
processor is kept in a purpose-built computer centre staffed by
personnel responsible
for maintaining it. Individuals in the organisation access the
mainframe computer
through terminals on their desktops in order to share common
organisational
resources, such as software programs or electronic data. As we use the
term today, a
mainframe is actually identified more by the ‘environment’ in which the
mainframe is
operated. In other words, the physical environment: the controlled
temperature and
humidity and the physical security of having the mainframe behind
locked doors.
Mainframe computers
are used as tools to support a given ‘business’ application such
as
• processing
applications for licences
• processing
government payroll information
• processing
financial accounts
• processing
environmental resource information.
In all of these
applications, the common denominator is the work process and the rules
for undertaking the
process. Everyone is undertaking a part of the whole work process
and everyone must
complete his or her work in accordance with the procedures
required to make sure
the job is done satisfactorily and the data are complete and
consistent.
For example, if ten people are responsible for
managing government payroll, each will
have a separate
responsibility. They will all have access to the same database through
the mainframe
computer, and each person must complete his or her task adequately
before the ‘job’ can
be considered complete.
The automation of a
given work process, such as processing government payroll
information, is often
viewed as an information system.
Information system: The combination of
information, technology, processes and people brought together to support a
given business objective.
The mainframe is the
data and application repository for most organisations. It is also
the hub for most
online business activities. It is believed that mainframes still house
90 per cent of the
data major organisations rely on to conduct their business. Despite
claims that mainframe
technology is dying out, sales of mainframe hardware and
software remain
steady. The term ‘mainframe’ has always had the image of being
something large in
size. Yet, however big the early ‘room-filling’ mainframes were,
today’s modern
versions are no bigger than the size of a household refrigerator. The
level of mainframe
sophistication has grown over the more than thirty years of its
evolution;
organisations still recognise its advantages in terms of performance,
reliability and
security.
NETWORK
COMPUTING
A network computing
environment is one in which an organisation has linked together
personal computers
that have been connected into a network. There are a number of types of
computer networks. Local area network: A computer network located within a relatively limited area such
as a building, agency or university campus. Also known as a LAN. Wide
area network (WAN): A computer network that covers a large geographical
area.
There are an
estimated 25 million computers connected to local area networks world
wide. The purpose of
networking personal computers and even mainframes together
is to permit
employees in the organisation to
• communicate
with one another as well as others outside the organisation, normally
through the use of
electronic messages
• access
information and services supported on the World Wide Web
• share
documents and data
• support
various work processes in the organisation based on the automation of
specific tasks.
A network environment
can range in sophistication from very simple to very complex.
Some networks are
used to support simple electronic mail communication. In other
networks, employees
may be able to share documents with each other and carry out
the work of their
work groups, project teams, etc. by exchanging electronic documents
through e-mail. The
most sophisticated organisations may have automated entire
work processes. For
instance, draft documents such as responses to letters sent to
senior officials, are
sent through various approval levels (such as action officer to
manager to director
to senior official) without ever being printed onto paper (except
perhaps the final
version, which needs to be signed by the senior official).
A computer network
can be simple and limited to a small number of computers or complex, linking a
large number of computers.
A computer that is
not connected to a network is referred to as a stand-alone
computer. When a
computer is physically connected to a local area network, using a
cable or other
communications channel, the computer becomes a workstation on the
network. Each device
on the network including workstations, servers, and printers is
referred to as a node.
Node: A processing location
on a network.
A workstation
normally has all of the usual resources found in the personal computing
environment (hard
drive, software, data and printer). However, users of workstations
will also have access
to network resources, which typically include application
software, storage
space for data files, and printers other than those on the local
workstation. On a
network, the network server typically provides the applications
software and storage
space for data files.
Network server: A computer that is
connected to the network and that ‘serves’ or distributes resources to network
users. Networks use different kinds of servers to carry out specialised
functions. For example, a file server is a computer and storage device dedicated
to storing files.
File server: A computer that
serves or distributes application programs and data files to workstations
within a computer network. The hard
drive of the file server is shared by the workstations on the network. Any
user on the network can store files on the server. Other types of servers
include a print server to manage one or more printers and a database server to
process database
queries. Most network
users will need to understand file servers because this is where they will store
their files on the network. A typical local area network uses a powerful PC as
a
file server. However,
a minicomputer or mainframe computer can also be a file
server. File servers
fall into three categories; dedicated, non-dedicated and application
servers. A dedicated
file server is devoted only to the task of delivering programs and data
files to
workstations. A dedicated file server does not process data or run programs
for the workstations.
Instead, programs run using the memory and processor of the
workstation.
In some cases, a
network computer performs a dual role as both file server and
workstation. When a
non-dedicated file server is used, the computer workstation
functions like a
normal workstation, but other workstations can access programs and
data files from the
hard disk of the user’s computer workstation.
An application server
is a computer that runs applications software and runs the
results of processing
to workstations as requested. An application server makes it
possible to use the
processing power of both the server and the workstation. Use of an
application server
splits processing between the workstation client and the network
server. The method is
also referred to as client/server architecture.
Some networks include
a host computer, usually a minicomputer or mainframe
attached with
terminals. A terminal has a keyboard and screen but does not have a
local storage device
and does no processing on its own. When a terminal is connected
to a host computer,
all processing takes place on the host.
The software on a
local area network typically includes many of the same applications
one might use in a
personal computing environment, such as word processing,
spreadsheet, database
management and so on. As the use of networks increase,
however,
organisations have begun to demand software that facilitate the flow and
sharing of documents.
This software includes groupware and workflow software.
Groupware: Applications software
that supports collaborative work between a group of users by
managing schedules, sharing documents
and undertaking intragroup communications.
Essentially,
groupware manages a pool of documents and allows users to access those
documents
simultaneously. A key feature of groupware is document version
management which
maintains all revisions within a document when more than one
group member revises
a document.
Workflow software: Software that
automates the process of electronically routing documents from one person to
another in a specified sequence and time.
Workflow software
facilitates a process or a series of steps. Workflow is based on a
‘process-centred
model’ as opposed to groupware’s ‘information-centred model’.
With workflow
software, the focus is on a series of steps. With groupware software,
the documents are the
focus. Peer-to-peer network: A type of network in which each
workstation has equivalent capabilities
and responsibilities.
Peer-to-peer networks
simply link a number of PCs together with no network server.
This is a cheaper way
of networking, and while files and printers can be shared the
wider advantages of
having a network server are lost.
The main advantage of
a computer network is that all the users can share resources,
rather than have
users each maintain his or her own resources. It is not necessary to
purchase multiple
copies of software; instead a licence can be purchased to use the
software within the
network which allows everyone to use the program at the same
time.
When a computer
network is used, finding, retrieving, and storing files on a network
is not very different
from the process used on a stand-alone computer. However,
when using a network,
security is much more of an issue. Information is now
accessible to a wide
group of people, and sensitive or personal information needs to be
protected.
An internal network
that belongs to an organisation and is accessible only by that
organisation’s
members is often referred to as an Intranet.
Intranet: An internal computer
network that belongs to an organisation and is accessible only by that
organisation’s members.
THE INTERNET
The Internet evolved
over the past thirty years from a fledging experiment with four
computers into a vast
information network that connects millions of microcomputers,
minicomputers and
mainframe computers. As of 1998, the Internet had more than 100
million users world
wide, and that number is growing rapidly. The Internet is
decentralised by
design and, remarkably, this anarchy by design works well.
Internet: A collection of
local, regional and national computer networks that are linked together to
exchange data and distribute processing tasks.
There are a variety
of ways to access the Internet, the most common being through an
Internet Service
Provider (ISP). An ISP is a company that charges an ongoing fee for
providing Internet
access to businesses, organisations and individuals. The ISP
provides the user
with the necessary communications software (such as e-mail) and
user account. The
user supplies a modem that connects the computer to the user’s
phone line. The
user’s computer dials the ISP’s computer and establishes a
connection over the
phone line. Once connected the ISP routes data between the
user’s computer and the
Internet. Most ISPs offer dial-up Internet connections and
electronic mail
access, along with additional services. Some ISPs offer direct access
to the Internet
without the use of proprietary software. The Internet connects millions of people
through a collection of computer networks.
A connection that
uses a phone line to establish a temporary connection to the Internet
is referred to as a
dial-up connection. When the user’s computer hangs up, the
connection is broken.
A phone line provides a very narrow pipe for transmitting data.
Its typical capacity
is only 28.8 thousand bits per second (bps). Using a phone line,
the time to transfer
the contents of a 680 megabyte CD-ROM would be over 53 hours.
More rapid digital
data transmission is now available from some telecoms providers in
various parts of the
world. The World Wide Web was created in 1990 as an easy-to-use source of
information.
World Wide Web: A computer network
system that allows users to browse through information available on computers
round the world. The World Wide Web opened the Internet to millions of people
interested in finding information. There are over one million Web sites around
the world and the number is growing very quickly. The World Wide Web consists
of documents called Web pages that contain information on a particular topic. A
Web page might also contain one or more links that point to other Web pages.
Link: A reference to
another document in an environment like the World Wide Web, that users can
go to directly by clicking on the
on-screen reference with the computer’s mouse. Links make it easy to
follow a thread of related information, even if the pages are stored on
computers located in different countries. Every Web page is stored as an HTML
(HyperText Markup Language) document.
HyperText Markup
Language (HTML): One of the main standards that controls how the World Wide Web works;
it is an SGML document type definition that determines how Web pages are
formatted and displayed and thus enables information to be exchanged on the
World Wide Web.
Standardised General
Mark-up Language (SGML): A metalanguage that can be applied to
documents in order to maintain their structure and context. An
HTML document contains special instructions called HTML tags that tell a Web browser
how to display the text, graphics, and background of a Web page. Web browsers
are used to view Web pages, transfer files between computers, access commercial
information services, send e-mail, and interact with other Internet users.
Web browser: A software
application that enables a user to locate and view pages on a Web site. Also
known as a browser. To
request a Web page the user either types in the URL (Uniform Resource Locator) address
or uses a ‘mouse’ to click on a Web page link.
Uniform Resource
Locator (URL): The global address of documents and other resources on the World
Wide Web. URLs can point to executable files that can be fetched using FTP
(file transfer protocol, ftp://) or a Web page that can be retrieved using HTTP
(hypertext transfer protocol, http://).
After the http://,
the next segment of the address is the server name. The server is the
computer and software
that make the data available. A Web server, for instance, is a
computer that uses
Web server software to transmit Web pages over the Internet.
Most Web servers have
domain names prefixed with WWW. By entering the Web server name, one accesses
the site’s home page.
Home page: The main page of a
Website. Typically, the home page serves as an index or table of contents to other
documents stored at the site (that is, the address).
Website: A location on the
World Wide Web. A home page is similar to the title page and table of contents in
a book. It identifies the site and contains links to other pages at the site.
The following is an example of a home page belonging to the ICA, viewed using a
particular type of browser software called Microsoft Explorer.
The Web browser is
the gateway to commercial information services as well as the
free sites on the
Internet. A commercial information service provides access to
computer-based
information for a fee. In 1997, approximately 17 million people
subscribed to the top
four commercial information services: America On-Line,
Compuserve, Microsoft
Network and Prodigy.
The server sends the
data for the Web page over the Internet to the computer. The
data includes two
things: the information the user wants to view and a set of
instructions that
tells the browser how to display it. The instructions include
specifications for
the colour of the background, the size of the text, and the placement
of the graphics.
Additional instructions tell the browser what to do when the user
clicks on a link. The
browser’s menu and tool bars help users navigate the Web as
they follow the
links. The Back and Forward buttons trace and retrace the users’ path
through the links
being followed from one Web page to another. The browser stores
and can display a
list of the pages being visited during each session. The browser can
also store a list of
favourite sites, often called bookmarks, to permit the user to jump
directly to the site
they wish to see instead of having to enter its URL every time.
Users can find
information on the Web by using a search engine. There are a number
of Web sites that
provide search facilities, and the Internet Service Provider will links
to these sites.
Search engine: A program that
searches documents for specified keywords and returns a list of documents where
the keywords were found.
SUMMARY
This lesson has
introduced basic information about three computer environments:
mainframe computing,
networks (such as Intranets), and the Internet, explaining key
terminology and discussing
how these environments work.
STUDY
QUESTIONS
1. What is a
computing environment?
2. What is a
mainframe environment?
3. Explain the
concept of an information system.
4. What is a personal
computing environment?
5. What is a network
computing environment?
6. Why might a
network computing environment be a valuable way for someone to work
within an
organisation?
7. What four things
does a network allow an employee to do?
8. What is a local
area network?
9. What is a wide area
network?
10. What is a network
server?
11. What is an
Intranet?
12. What are the
advantages and disadvantages of a computer network?
13. What is the
Internet?
14. What is an
Internet Service Provider?
15. What is the World
Wide Web?
16. What is a URL?
LESSON
3
COMPUTER
APPLICATIONS
Applications software
includes programs that users access to carry out work. This
lesson examines two applications
that may be of particular use to the student:
databases and
electronic mail (‘e-mail’). It introduces key concepts related to how
databases and e-mail
work.
Please remember, this
lesson is not intended to provide a comprehensive explanation
of the technical
details of all applications. Other applications would be word
processing,
spreadsheets and presentations. A brief description of these types of
software can be found
in Lesson 1.
DATABASES
A database is a
collection of information stored on one or several computers.
Database: A structured assembly
of logically related data designed to meet various applications but managed independently
of them. More specifically, a database is a self-describing collection of
integrated records. A database is self-describing in that it contains, in
addition to the user’s source data, a description of its own structure (such as
in a data dictionary). It is the data dictionary that make data independence
possible (for example, the database management system maps the data fields into
records and handles other similar transformation).
A database is a
collection of information stored on computers.
In the mid-1960s,
large organisations began to apply the power of mainframe database
technology to
administrative functions. As the term ‘computer’ implies, originally
most administrative
uses of computers were to process figures rather than text. These
were usually
activities involving high volumes of numerical calculations, where the
workflow was highly
predictable and routine. Typical examples include payroll,
accounts
administration or personnel data. These database applications were
primarily
organisation-wide transaction processing systems.
The limitations of
file processing prevented the easy integration of data. Database
technology held the
promise of solving these problems so large organisations began to
develop
organisational databases. Companies centralised their operational data, such
as purchase orders,
inventory and accounting data in these databases; these database
applications were
primarily organisation-wide, transaction processing systems.
Originally, database
processing was developed for use in the mainframe environment.
However, in the late
1970s to early 1980s, database technology began to move from
mainframes to PCs. As
a result, database management systems gradually became
more powerful and
easier to use. By the mid to late-1980s, PCs were beginning to be
linked together with
the aid of networking, which enabled computers to send data to
one another at
previously unimaginable rates. In time, users wanted to share their
databases as well;
this led to the development of multi-user database applications on
local area networks
(LANs).
Databases were
originally developed using mainframe computers but are now common on personal
computers and in networked environments.
Following is a brief
description of the concept of databases. In order to understand
databases, it is
important to begin with the data field.
Data field: A space allocated for
a particular item of information. In a database, fields are the smallest units of
information you can access. A data field contains a single piece of
information (first name, family name, ministry, employee number, salary and so
on). A collection of data fields comprise a record such as, in this example, an
employee record.
Database record: A complete set of
information in a database; records are composed of fields, each of which contains
one item of information. A collection of records (in this case, employee records) comprises
a database. Structured databases typically store data that describes a
collection of similar entities. ‘Salaries and benefits’ is an example of an
entity; ‘education/training’ is another entity. A n employee database stores
data about the employees in an organisation. A
medical database
stores data for a collection of patients. An inventory database stores
data for a collection
of items stocked in a warehouse.
Data structure: A scheme for
organising related pieces of information. The basic types of structures
include: files, lists, arrays, records, trees, tables. Each of these basic
structures has many variations and allows different operations to be performed
on the data.
There are three basic
database models.
• Hierarchical
databases exhibit a branching structure, with information arranged
into sets and
sub-sets; getting to a particular piece of data may require going
through several
vertically ordered files. An example is the process involved in
finding a distant
cousin on a family tree.
• Network
databases offer many more direct connections between files, but,
similar to
hierarchies, the links are predefined and are difficult to change or adjust.
• Object-oriented
databases link self contained entities (or objects) together.
Objects can be text,
a picture, a piece of film or any item that can be individually
selected and
manipulated. This kind of database is particularly useful for
organising large
amounts of disparate information, but they are not designed for
structured numerical
analysis.
The limitations found
with these types of databases explain why most organisations
have turned to
relational databases. Relational databases not only accommodate
multiple views but
allow new links to be forged as needs arise. Relational databases
are powerful because
they require few assumptions about how data is related or how it
will be extracted
from the database. As a result, the same database can be viewed in
many different ways.
Relational database: A database that
spreads information across different tables while maintaining
links between them. A
relational database stores facts in tables called relations. The only
requirement is that the information must be capable of being laid out in rows and
columns (similar to a list of names, addresses and phone numbers). An example
from a university might help to illustrate the concept. In a very simplified
view of a university database, each
facet of the
university’s administration would be represented by a table containing
information within
the remit of a single department. The admissions office, for
instance, keeps track
of students by ID number, name and major field of study. The
personnel office
keeps records of the department, rank, names, and social identity
numbers of the
teaching staff, and so on.
A relational database
stores information across different tables and connects them with links in the
computer.
If these tables are Isolated
from one another, these tables would be nothing more than a simple computerised
filing system. Tied together, however, they become a database, with
each table offering
access to the information held by all of the others. This versatility
stems from deliberate
duplication of columns in two or more tables, resulting in a tool
called a common key.
If, for example, two tables containing information about
students each possess
a column containing student identification numbers (ID) then
this number can be
used to find the row in each table that contains information
applicable to any
student. Each column in a table represents a single data attribute, or
characteristic, of the table’s subject. A column might contain, for instance,
the identification numbers of the students or each professor’s department.
Each row, or record,
in a table contains all the information about a single entry. In the
case of a student, a
record might include, in addition to an identification number, the
individual’s first
and last names and major course of study.
Belonging to both a
row and a column, an occurrence is the basic unit of a relational
database table. The
occurrence contains the value of an attribute of a single record. In
some cases, the value
is a string of letters making up a word or words, in others a set
of numerals, such as
a student’s identification number or job title.
Officials in the
admissions, personnel, and finance offices have direct access to each
other’s information
through the ‘Dept’ attribute, common to all the tables. Similarly,
tables in the
admissions and registrar’s offices are joined by the ‘ID’ attribute for the
student
identification number. Relations in the registrar’s and finance offices are
connected by a
‘section’ attribute that identifies subdivisions of courses.
Attribute
Menu: A collection of
onscreen choices given to the user to help him or her interact with a computer
system. Database menus are similar to those used in most software. They
are typically
arranged as a
hierarchy so that after the user makes a choice at the first level of the
menu, a second series
of choices appears.
Keyword searching
permits access to databases through the use of keywords.
Keyword search
engine: A program that allows a user to search a database by an index
entry that identifies a specific record or document. Keyword
search engines are especially popular for searching the many documents stored
in a free form database such as the World Wide Web. To use a keyword search engine,
the user types in a word and the search engine locates areas in the database where
the word or related information can be found. When information in a database
needs to be accessed quickly, it is usually stored as a structured database.
However, the structure in structured databases can cause a problem for users
who might not know the format for the records in a database. One way to help
users search structured databases is by providing a ‘query by example’ user
interface based on the use of a query language.
Query language: A set of command
words that can be used to direct a computer to create databases, locate information,
sort records and change the data in those
records. One query language is
called SQL (structured query language). The use of query
language is based on
knowledge of the command word and the grammar or syntax that
will let one
construct valid query sentences. For example, the SQL command word
for finding records is
SELECT. WHERE is used to specify that only certain rows of
the table are
displayed. For example, SELECT employee ID no from employee
statistics table
WHERE position = ‘Manager’.
In more sophisticated
systems, queries can also be formulated in a natural language
such as standard
English, French, or Japanese. In order to use the natural language,
the user is not
required to learn a query language. Queries can be straightforward such
as: ‘What records of
World War Two are available in the archival institution’? This
form of searching is
still under development although examples of its use are
spreading rapidly.
Users can ask
questions of the database using a variety of query languages, which formulate
questions so that the computer can perform operations and provide results.
COMMUNICATING
BY COMPUTER
Communicating via
e-mail is rapidly becoming as important as telephone and fax
communication and
forms an important component of any office automation system.
Electronic mail
(e-mail): A way of sending messages between people anywhere within an
organisation or in the world using a computer that can communicate with another
computer through a computer network. The message or document can be
viewed on a computer
screen and printed out. E-mail
is handled by a variety of software programs such as Microsoft Outlook Express,
Eudora, elm, pine and so on. The message originator creates a message file
in the e-mail
software editor. When complete, the message is posted to a message
transport system that
assumes the responsibility for delivering that message to its
recipient(s)
‘mailbox’.
To receive and read
the message, the recipient runs a software program that retrieves
incoming messages,
allowing the messages to be filed, listed, forwarded or replied to.
Generally a single
user-interface program is used to send and receive messages both
locally and
worldwide. Users do not need to have the same e-mail software program
as the person they
are corresponding with. The e-mail itself may consist of simply a
message or may carry
with it attachments containing files created in a variety of
software
applications, for example word processed documents or spreadsheets.
Electronic mail is a
method for communicating messages electronically using computer networks.
The ability to send
email depends on having an Internet Service Provider and a
modem, or being
linked into a larger university, government or company network.
Being linked into a
larger network requires a user to have a network card in the
computer and access
to network cabling. There are various networking standards.
One of the most
common is ‘ethernet’.
Ethernet: A local area network
(LAN) protocol that supports data transfer.
Open networks allow
users to send e-mail internally, to colleagues in the same
organisation, and
externally via the Internet. Some organisations have private
networks that allow
staff to send e-mail all over the world, but not outside the
organisation.
Network
administrators or Internet Service Providers will give users an email address.
This is usually in
the format xxx@yyy.zzz. The first part of the address before the @
sign is the
individual user’s name or identifier. The second part of the address is split
into at least two
parts (sometimes more), each part divided by a full stop or period.
This part of the
address indicates which company or university the user works for, or
which ISP they are
using, or even which country they are based in.
For example a user on
America-Online would have the address: auser@aol.com. A
user in the British
University College London may have the email address:
zzz999@ucl.ac.uk. In
this address, the user has been given the code ‘zzz999’ by the
university. The rest
of the address shows that ‘ucl’ is University College London, that
it is an academic
institution (‘ac’) and that it is based in the UK (‘uk’). There are a
number of different
types of email addresses, including .com, .org, .co.uk and so on.
The following figure
is an example of an e-mail message received using Microsoft
Outlook Express
electronic mail software that includes attachments.
SUMMARY
This lesson examines
two particular applications of particular use to the student:
databases and
electronic mail (‘e-mail’), examining key concepts related to how
databases and
electronic communications work.
STUDY
QUESTIONS
1. What is a
database?
2. What is a data
field?
3. What is a database
record?
4. Explain the value
of storing information in a database.
5. What is a
relational database?
6. What is the
concept of query language?
7. What is electronic
mail?
8. Briefly explain
how electronic mail works.
LESSON
4
WHAT
TO DO NEXT?
This
module has been written to familiarise records and archives
reader with some of the basic concepts of computers. As well, this module has
explained some of the key terms people will encounter as they work more and
more often with information technology specialists. This module introduces important
terminology, offers definitions and explains how the concept in question may
affect records or archives work. This module has presented
introductory
information and should not be considered by any means a complete
discussion of
computerisation.
ESTABLISHING
PRIORITIES FOR ACTION
This module has
introduced basic information about computers. Once you understand
these concepts, the
next step is for you to consider what to do next. As this is a basic
module on
computerisation, you need to determine the best course of action for you as
a student and for you
as a representative of your organisation. Should you continue
with further reading
on the topic? Should you proceed with the study of related
modules in the study
programme? Each institution will make different decisions
based on its
administrative environment and short- and long-term plans. However, it
is possible to offer
some recommendations for action, to help the institution
understand its
computer needs. Complete the activity below then consider the
suggestions offered.
Priority
1: Discuss Computers with Colleagues and
Friends
Take every
opportunity to discuss computers with your colleagues, with friends or
with others in the
field. You can only benefit from reviewing topics with others, even
though their opinions
might leave you confused from time to time! It is important to
ask as many questions
as possible, as some topics that seem straightforward are in fact
quite complex and
require considerable thought.
Priority
2: Practice Using Computers
If you have access to
a computer, practice using it as much as possible. You may be
familiar with some
functions; try to learn about others. You may not know how to
type; take advantage
of any free time to learn how to use the keyboard comfortably. If
you have access to
databases or the Internet, work with them whenever you can to
learn more about how
they work. Bear in mind, though, that you could soon suffer
from ‘information
overload’. Be sure to balance your work on computers with
reading other modules
or doing other work.
Priority
3: Attend Training Courses
Whenever possible,
try to attend training courses, workshops or seminars on computer
issues. Perhaps your
organisation offers in-house training, or a local college or
institute provides
courses on computer issues. Try to study as much as you can, but
remember it is wise
to focus first on those skills that you can use and practice in your
day-to-day work. It
is difficult to learn and remember computer skills if you do not
practice them
regularly.
For more details email: vashist.subhash@gmail.com
No comments:
Post a Comment