1. technology and computing
2. hardware
3. computer

Form 3
Computer Studies
INPUT AND OUTPUT DEVICES
1.
An Overview of Input and Output Devices
Input, Output and Secondary Storage Devices are collectively known as peripherals
The processor or Central Processing Unit (CPU) makes all the calculations of the computer. In
order for a process to be possible we need to feed in data to the computer through the input
devices. The computer will then process the data according to a particular program and finally
deliver information through the output devices. If the information produced needs to be stored
for the future, we will store this into a secondary storage peripheral device.
Input
Device
Computer
Output
Device
INPUT
PROCESS
OUTPUT
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Input and Output Devices Examples
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<< Input Devices >>
Input devices are all those hardware equipment that are used to enter data into the computer.
Keyboard
This is the most common and widely used input device. There are different types of keyboards
but the QWERTY keyboard is the most widely used. Apart from the normal alphabetical keys,
the keyboard has:
-
A Numeric Keypad
-
Navigation Keys
-
Function Keys
Function keys change function used according to the application being used.
Mouse or Trackball
The second most commonly used input device is the
mouse. The mouse helps the user to point and access
items on the computer. Its main function is to control
the cursor or pointer on the computer’s screen.
The mouse can have 2 or 3 buttons, used according to
the software application being used. Today, most mice
also have a scroll wheel which is used mainly to scroll
through documents.
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The trackball has the same basic functions of the
mouse. The only difference is that the trackball is
stationary and one doesn’t need to move it on a mouse
pad.
In order to navigate with the pointer, the user must
move a ball situated at the top of the device. Similar to
the mouse, the trackball has 2 or 3 buttons used to
select items from the screen.
Touchpad
This is a small sensitive pad used on portable computers
(laptops).
The touch pad is used as a pointing device. The pointer is
moved on screen by touching the touch pad with the finger.
Tapping on the touch pad will give the same results as when
using the mouse buttons. The touchpad is particularly
useful for persons with disability whom can have limitations
in moving their hand.
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Advantages
Disadvantages
- Relatively inexpensive
- When gripped too tightly
- Very little finger movement
can cause muscle strain
needed to reach buttons
- Uses more desk space than
other pointing devices
- Must be cleaned regularly
- Uses less desk space than
- Wrist is bent during use
mouse
- More finger movement
- Requires less arm and
needed to reach buttons
hand movement than
than with other pointing
mouse
devices
- Small footprint
- Places more stress on
- Least prone to dust
index finger then other
pointing devices do
- Small active area makes
precise cursor control
difficult
Scanner
The scanner is a device that transfers printed text
and images to a computer. Today, most home
users have a scanner connected to their
computers. These are generally called flatbed
(others less common such as barcode readers are
called handhelds). The scanner alone is not
enough to capture the data and transform it to a
format that can be understood by the computer.
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In fact, one needs a number of software:
•
Driver Software – Used to control the scanner hardware.
•
Photo Editing Software – Used to edit scanned photos
before being stored, printed or used in projects or
websites.
•
Optical Character Recognition Software (OCR) – When a
printed document is scanned, normally this is stored as
an image and thus the OCR is used to convert this
picture to word processing format for editing.
Joystick
This device is well known with young people as it is mainly
used for playing computer games.
As the name implies, it is like a stick connected to a platform,
which can be moved in all directions.
These movements in turn will move something on screen
depending on the game. Usually joysticks have buttons also
called triggers.
Barcode Reader
When we buy products from shops we usually see small
labels containing white and black stripes called barcodes.
These labels contain information on the product. In order to
read this information, one must pass the barcode in front of
a special reader. This reader can be in a form of a pen or
installed on the shop’s counter. The barcode reading
consists of a light emitting diode that will emit light on the
code.
The reflected light from the barcode is translated to the computer by a light sensitive diode.
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Computer Studies
Optical Mark Reader
This device reads marks in predetermined places on specially prepared
cards. These are usually used in multiple-choice questions.
The student will have to fill a space with a pencil, usually HB.
The filled examination paper is then inserted into the OMR so as to
enable it to read the answers marked.
Magnetic Ink Character Reader (MICR)
This system uses special ink to write numbers with coded magnetic ink. This special ink
contains the written numbers magnetically. This system is widely used on cheques issued by
banks. The MICR is much faster than OCR or other methods when reading codes and thus
identifying cheques.
1
2
3
4
Federal Reserve
Branch / City
Bank Number
Parity Check Digit (for
District, 2 digits: 01 to
Designation &
12
Clearing
reading error control)
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Graphics Table
Professionals, such as draftsmen and engineers,
usually use this input device. It is used to speed up
their drawing work. The device consists of a hand
held operated device (similar to a pen) used to trace
diagrams placed on a digitised table. The drawing
will then be transferred to the computer.
Pen
Pens are used on hand held computers such as PDA’s (Personal
Data Assistant). These hand held computers have a special
sensitive screen.
When the user touches the screen it will interact with the
computer
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Summary of Input Devices
Input Device
Advantages
Disadvantages
Keyboard
Typists can use with ease
Relatively slow
Mouse
No typing skills are required
At times can be tricky to use
Light Pen
No typing skills are required
Needs much software to make
it versatile
Bar Code Reader
Quick and easy entry of data
Needs specialized software
under non-ideal conditions
OCR
Can be programmed to read
Elaborate hardware and
text and neat handwriting
software required, needs
training
Mark Reader
Fast input
Elaborate hardware and
software required
MICR
High volume, very reliable
Only 14 characters are
represented
Joystick
Easier than keyboard
Special interface needed
Digital camera
Easy image capture
Still relatively costly
Graphics Tablet
Enables operator to enter
Slow
pictures
Speech Reader
No hands needed
Limited vocabulary
Touch Screen
Easy operation
Needs specialised hardware
Intuitive
and software
Can have add-ons for
Relatively slow
Hand Held Terminals
sophisticated operations
Scanner
No artistic performance
High quality graphics require
required
large amounts of disk space
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< < Output Devices >>
After processing the inputted data, the computer will give its output. This output can be in two
different formats:
OUTPUT as
Softcopy
INPUT
PROCESS
OUTPUT as
Hardcopy
•
Softcopy – Visual (monitor) or Sound (speakers)
•
Hardcopy – Output on a tangible (something you can touch) such as a printer printout.
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Monitor or Visual Display Unit (VDU)
The monitor is the most common type of output device and is also called Visual Display Unit
(VDU).
Visual Display Units
1. Monochrome – This type of display uses
2. Colour – This type of display uses more
only one type of colour or a greyscale
than one type of colour and is generally called
RGB monitors. The RGB stand for Red, Green
and Blue and a combination of these colours
are used to display the image on the monitor.
Colour monitors can display range from 16 to
16.7 million colours.
Resolution
This term refers to the clarity or sharpness of a printout or display screen. The more pixels there are per
square inch, the better and greater the resolution.
1
1
LOW Resolution
HIGH Resolution
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One can find different standards for monitors. They support different colour depths (number of colours
it supports). The most common standards for monitors are:
1. VGA (Video Graphics Array) mode appeared in 1987. It offered a resolution of 720x400 in text
mode and a resolution of 640 by 480 (640x480) in 16-colour graphics mode. It also offered a
resolution of 1024 x 768.
The VGA quickly became the baseline display mode for PCs.
2. SVGA (Super Video Graphics Array) is a graphics mode which can display 256 colours at
resolutions of 640x200, 640x350 and 640x480. SVGA can also display higher definitions such as
800x600 or 1024x768 by using fewer colors.
3. XGA (eXtended Graphics Array). is an IBM display standard introduced in 1990. Today, it is the
most common appellation of the 1024 × 768 pixels display resolution, but the official definition is
broader than that. It was not a new and improved replacement for Super VGA, but rather
became one particular subset of the broad range of capabilities covered under the "Super VGA"
umbrella.
The initial version of XGA expanded upon IBM's VGA, adding support for two resolutions:
•
•
800 × 600 pixels with high color (16 bits per pixel, i.e. 65,536 colors).
1024 × 768 pixels with a palette of 256 colors (8 bits per pixel)
The Different Types of Monitors
The different types of monitors are:
Cathode Ray Tube (CRT) – uses the same technology as used in
television
sets.
The CRT uses a vacuum tube in which an electron gun is installed.
When
electrons fired by the electron gun touch the phosphor layer situated
at the
internal side of the screen, this will glow. This dot of light is called a
Pixel.
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Liquid Display Unit / Liquid Crystal Display (LCD) – we usually find this installed in laptops and handheld
computers. The technology used is different from that of the CRT. LCD uses tiny capsules filled with
liquid crystals. When the molecules of the liquid are subjected to an electric field, the liquid crystals align
and light reflects off them.
Without the field, their alignment reverts to its original, nonreflecting arrangement, so the elements appear dark.
Combinations of LCD’s are arranged to form patterns of reflected
light that spell out numbers, symbols or letters.
TFT (Thin Film Transistor) is a variant of LCD which uses thin
film
transistor technology to improve image quality.
Summary of Video Glossary
CRT
Cathode ray tube (monitor)
VDU
Video display unit (monitor)
LCD
Liquid crystal display – as available on hand held games and potables
Pixel
The smallest area on a screen, seen closely as a tiny dot
14” 15” 17” 21”
This is the length measured in inches (1 inch = 2.54cm) of the screen measured
diagonally, that across two corners.
VGA
Video graphics array, this provided,
1. Introduced analogue monitors to the computer system; that is colour was no
longer restricted to fixed colours but allowed different hues and colour
blending.
2. Graphics resolution of 1024 x 768 pixels
3. Allows 256 colours
SVGA
Super Video Graphics Array
As above but allows 16.7 million colour hues
Bit map
Computer memory that represents a video image
Side NOTE:
A terminal is an integration of a VDU with a keyboard. There are two types of
terminals, namely INTELLIGENT TERMINLAS (having a CPU) AND DUMB TERMINALS (no CPU)
-
Intelligent terminals can do some local processing of data and then communicate with a main
computer just to relay the results
-
In a dumb terminal, all processing must be done through the main computing system
Printers
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Printers are output devices that transfer the output of the computer on paper (hardcopy). The printers
can be divided into two categories Impact and Non-Impact:
•
Impact – refers to all those printers whose printing heads touch the paper. An example is the
Dot matrix printer.
•
Non-Impact – are all those printers whose printing heads do not touch the paper. An example
is a Laser or an Ink-Jet printer.
The following is a list of the different types of printers that exist:
Daisy Wheel Printers
This type of printer is rarely used any more since new printer technology, which is more efficient and
economic, has been discovered. The principle of this type of printer is that number and letter are each
situated on metal leafs as shown.
These leafs make part of the daisy wheel. In order to print, the daisy wheel rotates while a hammer will
strike each character, which will make contact with the printer ribbon and the paper.
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Line Printers
As the name suggests these type of printers will print one whole document line at one go. There are two
basic types of line printers:
1. Barrel Printers – This printer has a number of disks each containing all the letters and
numbers. These disks are situated one near each other on a shaft and can rotate
independently from each other. Lines are written by revolving each disk in the correct
position in order to form a complete line. A row of hammers will strike the ribbon and
papers.
2. Chain Printers – All the alphabet and numbers are imprinted on a chain. In order to
write on paper, a hammer will strike the right characters to print.
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Dot Matrix Printers
Dot matrix printers are categorised as character printers because they write one character at a time. The
printing head is made up of several pins, which form a column. The printing head is attached to a belt
which moves it from side to side along the width of the paper and at the same time the paper is rolled up
by means of a roller. In order to write, the head pins are fired with the aid of an electro magnet, which
hit the ribbon and paper.
Inkjet Printers
These types of printers are the most popular nowadays. It is basically what most home users have
today. These printers have good resolution, are silent and for small amount of printing are not
particularly expensive. These printers are called page printers.
There are two types of technologies used:
1. The first type (called Bubble Jet) has a chamber containing ink. The ink is heated up with tiny
electrical heaters. This will cause the ink to expand and form a bubble. The bubble will burst
and the ink transferred on paper.
2. The second type (called Ink Jet) uses a piezo quartz nozzle. When electricity is passed through
it, it vibrates and transfers the ink on paper.
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In the inkjet printing mechanism, the print head has several tiny nozzles, also called jets. As the
paper moves past the print head, the nozzles spray ink onto it, forming the characters and
images.
Laser Printers
Laser printers offer the best quality in terms of printout quality and
resolution. On the other hand they are the most expensive to run.
Laser printers are called page printers since they print one page at a go.
The laser printer uses a laser beam, a drum and a toner.
Summary of Printer Classification
Printer Classification
Printers can be subdivided into four groups
CHARACTER
LINE
GRAPHICS
PAGE
Prints character at a
Prints a whole line at
Printers used for
Prints a whole page at
time
a time
graphics such as CAD
a time
Printer Glossary
CPS
characters per second (how many characters it is able to print in 1 second)
NLQ
near letter quality (very good print)
Draft Mode
lowest printable resolution, it is also the quickest but not the best output, it is
usually used for spell checking before the actual print
DPI
dots per inch, this gives the resolution of the print, the higher the dpi the higher
the resolution – more clear
Resident
available on board (the printer) usually fonts or buffer memory
Scalable
can be set in different sizes.
Example: a
Font
a a
aa
aa
typeface or particular type of written characters
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Example: Tahoma, Times New Roman, Arial
Spooling
A printer works relatively very slow when compared to a CPU. In order to free
the CPU to attend to other tasks during printing, the printing job (file) is
temporarily stored on disk, tape, or memory. The printer will then receive the
file to print chunk by chunk – enough to keep it busy. This compensates for
slow operating speeds of some peripheral devices. When spooling is to a
printer’s memory, this is also known as memory buffer.
Memory buffer
Printers have memory buffers to speed up their operation. Printing speeds are
very slow compared to computer speeds and the printing job is spooled to a
printer’s memory buffer. This is usually in the region of 10k to 50k RAM on small
office printers. The computer downloads quickly in the fraction of a second the
printing job to buffer memory. When the data in the buffer is exhausted, the
next chunk of printing data is downloaded again by the computer in a split
second. Sophisticated printers use large memory buffers and buffer area may be
split into two separate memory areas.
Side NOTE:
On-line or Off-line
A peripheral device may be off-line or on-line
ON-LINE:
refers to when a peripheral device is under the control of the CPU i.e. connected
to the computer and usable
OFF-LINE:
refers to when a peripheral device is not under the control, and cannot be
controlled by the CPU
Plotters
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The plotter uses pens to write on paper and is usually used for engineering drawings. There are two
types of plotters:
1. Flatbed Plotter – This uses a flat paper which is fixed, and pens (or styluses) that move on it
draw the required design.
2. Drum Plotter – Here the paper moves along a drum vertically while pens move side to side
horizontally.
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Summary of Output Devices
Output Device
Advantages
Disadvantages
Dot Matrix Printer
Versatile graphics and text,
Average quality, slow speed
cheap
Daisywheel Printer
Letter quality print
Very slow, no graphics
Chain Printer
Fast
No graphics
Line Printer
Can cope with high volumes
Very noisy, average quality
Thermal Printer
Quiet
Special paper needed
Ink – Jet Printer
Very quiet
Ink smears occasionally
Laser Printer
High quality, fast
Expensive to run
Flatbed Plotter
Large paper handling
Very expensive
capabilities
Drum Plotter
Large paper handling
Very expensive
capabilities, occupies less
space
Microfilm Viewer
Very small
Needs special machine to view
VDU
Fast output, vivid colors
Radiation (High on CRT and
low on LCD)
Speech Synthesizer
Do not need to use eyes
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Limited sound range
Form 3
Computer Studies
Vector and Raster
Vector – Is a line calculated in two dimensions
and is
defined by its end points, which are x-y
coordinates on a grid. Thus pictures are
composed of mathematically-defined geometric
shapes
such as points, lines, arcs and other geometric
figures.
If the picture or diagram is enlarged, it does not
affect
the quality. Vectors are best used where high
contrast and colour is needed such as the design
of
logos and geographical maps
Vector images have many advantages, but the
primary disadvantage is that they're unsuitable for
producing photo-realistic imagery. Vector images
are
usually made up of solid areas of colour or
gradients, but they cannot depict the continuous subtle tones of a photograph.
Raster – The picture image is created using a
complex series of dots or pixels.
Raster stores the colour of each pixel in
memory, and thus one needs a lot more
memory than if using vector. Thus the overall
picture will occupy more memory on the
storage media. Raster pictures can be
enlarged but they tend to lose quality.
Raster images are also known as bitmap
images. These type of images use bits (1 or
0)
to describe each pixel’s attributes such as
colour. The quality of a raster image depends
entirely on the image resolution.
Soundcard and Speakers
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These devices are used to produce sound from the computer system. The soundcard is a card installed
in the tower case of the computer. Its role is to convert the signal coming out of the computer to a
format that can be reproduced by the external speakers.
Computer Categories
Special Purpose (Dedicated) Computers:
These are built to solve only one particular task. VCR
and Optical recorders/players, Auto-pilot, Automatic Washing Machines, Mobile Phones, GPS, etc. will
have an embedded computer to control them. The program for these computers is normally ‘hard coded’
that is built in the machine’s ROM (Read Only Memory).
Embedded systems controlling common appliances are one form of dedicated computers – they have a
CPU, Input Output devices, software stored in ROM and some RAM as workspace.
General Purpose Computers:
On the other hand, these can perform more than one
task provided that the correct instructions are loaded in the computer, therefore depending on what
PROGRAM we load, the computer may act differently.
Examples:
- Computer + ‘Word’
used for word processing – typing
- Computer + ‘Excel’
used for accounting purposes – spreadsheet
- Computer + ‘Paint’
used for drawing
- Computer + ‘AutoCAD’
used for designing layouts – architects, engineers, etc.
SECONDARY STORAGE DEVICES
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Secondary storage devices cannot be classified under input or output devices. These devices are used to
store data for later use.
Secondary storage devices can be categorised in 3 main groups:
1. Magnetic
2. Optical
3. Electronic
1. Magnetic Storage
Magnetic storage devices store the data on a magnetic layer. Examples of such devices are:
a. Floppy Disk
b. Hard Disk
c.
Magnetic Tape
The technology used is very simple to understand. The magnetic layer is magnetised when there is a
binary 1 and left un-magnetised when there is a binary 0.
Floppy Disk
Floppy disks store small amount of data typically not larger than 1.44MB. These small diskettes are used
mainly to transport small files from one computer to another.
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The construction of the floppy is basically a plastic disk coated with magnetic material, enclosed in a PVC
jacket to protect the magnetic material.
In order to write data to a floppy this must be first formatted. This procedure involves the creation of
sectors and tracks. On the diskette, data is recorded on closed concentric rings (tracks).
Each track is divided into sectors. These are invisible wedged-shaped sections used by the computer for
storage reference purposes.
Data Access Area
Hard Plastic Jacket
Metal protective plate (shutter)
that moves aside (in disk
drives) to expose data access
are on disk
Label
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Hub
Write Protection notch. The
notch in this diagram shows
that the floppy disk is not
write protected.
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Hard Disks
As the name implies, hard disks are built with metal or glass platters covered with a substance that
allows data to be held in the form of magnetised spots. Today hard disks are composed of more than
one disk (also named as platter), which are stacked on each other. This technology gives the possibility
of having large storage capacity. Typically computer systems today have an 80GB (or more) hard disk
capacity.
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Magnetic Tape
This type of storage media is used in large computers where large amounts of data are stored. The tape
is made up of a thin plastic tape having horizontal running tracks and vertical frames. The data to be
stored is divided into:
a. The Header – Including file name and number of blocks
b. Block – of data separated by inter block gaps
c.
Trailer – containing number of blocks, to be used as cross reference with the header
Examples – Reel to Reel tape drive and Cassette Tape drive
Magnetic tape is ideally suited to store a list of records whose sequential order is sorted for later
processing. Payroll systems and record updating is ideal for tape. A sorted tape can be used to issue
pay cheques, update a list of customers etc.
Protection of Magnetic Storage
1. Do not put media in areas where magnetic field is present
2. Do not bend (Floppy Disks and Tape)
3. Do not store in high temperatures and / or in humid areas
4. Do not store in dusty environment
2. Optical Storage
The CD-ROM Disk
CD-ROM stands for Compact Disk – Read Only Memory. This is an optical disk where information is
stored at the time of manufacturing.
Examples of CD-ROM are Music CD’s and software that one buys from computer shops such as games.
Optical disks write data with a high power laser beam, which records data by burning tiny pits onto the
surface of the disk. In order to read data, a low power laser beam reads data by reflecting smooth
areas, which are interpreted as 1 bits, and not reflecting pitted areas which are interpreted as 0 bits.
The typical storage capacity of a CD-ROM is 650Mb, which makes them a very versatile data storage
media when it comes to store data for short and long term periods of time.
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Re
adi
ng
Dat
a
Re
adi
ng
“1”
The
lase
r beams reflects off the smooth surface, which is interpreted as a 1 bit.
Reading “0”
The laser beam enters a pit and is not reflected,
which is interpreted as a 0 bit.
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CD-R
CR-R which stands for Compact Disk- Recordable is a CD format that allows users to use a CD-R drive to
write data, only once, onto a specially manufactured disk that can then be read by a standard CD-Rom
drive.
CD-RW
CD-RW stands for Compact Disk – Rewritable. This type of media allows users to copy and erase data.
Thus, this disk can be used over and over again.
DVD-Rom
DVD-Rom stands for Digital Video Disk or Digital Versatile Disk. This optical disk looks like a normal CD
but in fact, it can store much more data than a CD
The following is a list of the most common DVD types with their respective capacities:
a. Single Sided / Single layer – 4.7Gb
b. Single Sided / Double layer – 8.5Gb
c.
Double Sided / Single layer – 9.4Gb
d. Double Sided / Double layer – 17Gb
Typically, these types of disks are used to store movies as well as modern computer games where a large
amount of data is required.
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3. Electronic Storage
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Electronic memory is the latest technology in secondary storage media. This is also referred to as Flash
memory.
Flash memory is non-volatile solid-state computer memory storage that can be electrically erased and
reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general
storage and transfer of data between computers and other digital products. It is a specific type of
EEPROM (Electrically Erasable Programmable Read-Only Memory)
This type of memory media has no mechanical moving parts and thus it offers some advantages when
compared to the other type of media.
Advantages:
1. Very small
2. Does not consume a lot of energy in order to function
3. Noiseless
4. Limited heat emission
5. Portable
Disadvantages:
1. Limited amount of memory capacity when compared to the other type of media (Currently big
advancements are being made and the maximum capacity of this media is 60GB).
Because of their small size and big capacity, electronic memory is suitable to be used in portable devices.
Today electronic memory is being used in Digital cameras, Mp3 Players, PDAs, Mobile phones and
Laptops.
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Data Access Methods
We have two types of data access methods:
a. Serial Access:
- Cassette tape
- Tape Stream
b. Random (Direct) Access:
- Floppy Disk
- Hard Disk
- Zip Disk
- CD-Rom
- DVD
- Flash Memory
Serial Access VS Random Access
Imagine one has a thousand records stored on a secondary storage device and one needs to access the
543rd record. In serial access, one has to access the preceding 542 records before homing in on to the
543rd record.
On the other hand, in random (direct) access, one is given the possibility to go directly to the
particular record required.
Serial Access Method
Serial access is where the items are read, one at a time, from the physical start of the file, in the order in
which they are stored.
Data is stored on tape in Binary Coded Decimal Format. A tape is made up of horizontally running
tracks and vertical frames. When a file is stored on tape, the program is divided into:
a. a file header (including the file name and number of blocks)
b. number of blocks (of a fixed number of records), each separated by inter-block gaps
c.
a trailer (with the number of blocks for cross checking with the program header)
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In serial access methods, as a means of security, parity checking is used. This is a means to check
tape data integrity. Horizontal parity utilises a tape track for checking whilst Vertical parity uses a
frame for parity checking. Both can be used for optimum integrity and error correction.
There are two types of parity systems – Odd and Even parity. In even parity, the tape drive ensures
that both horizontally and vertically, there is an even number of 1’s. This system works similarly for odd
parity. The only difference is that the 0’s are used instead of 1’s.
An even parity bit is set to 1 if the number of ones in a given set of bits is odd (making the total
number of ones, including the parity bit, even).
An odd parity bit is set to 1 if the number of ones in a given set of bits is even (making the total
number of ones, including the parity bit, odd).
Parity Bit Summary
- Even Parity
a. Set to 1 if number of 1’s is odd
b. Set to 0 if number of 1’s is even
- Odd Parity
a. Set to 1 if number of 1’s is even
b. Set to 0 if number of 1’s is odd
Transmission sent using odd parity:
a.
b.
c.
d.
e.
A
A
B
B
B
wants to transmit: 1001 A computes parity bit value: (1^0^0^1) = 1
adds parity bit and sends: 10011
receives: 10011
computes overall parity: 1^0^0^1^1 = 1
reports correct transmission after observing expected odd result.
This mechanism enables the detection of single bit errors, because if one bit gets flipped due to line
noise, there will be an incorrect number of ones in the received data. In the two examples above, B's
calculated parity value matches the parity bit in its received value, indicating there are no single bit
errors. Consider the following example with a transmission error in the second bit:
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Transmission sent using even parity:
a.
b.
c.
d.
e.
A
A
A
B
B
wants to transmit: 1001
computes parity bit value: 1^0^0^1 = 0
adds parity bit and sends: 10010 *** TRANSMISSION ERROR ***
receives: 11010 B computes overall parity: 1^1^0^1^0 = 1
reports incorrect transmission after observing unexpected odd result.
B's calculated parity value (1) does not match the parity bit (0) in its received value, indicating the bit
error.
Even Parity Example
1
0
0
0
1
0
0
1
0
1
Even
Parity
Track
1
1
1
1
1
1
1
1
1
1
T
1
1
1
1
1
1
1
1
1
1
R
0
0
0
0
0
1
1
0
0
0
A
0
0
0
0
0
0
1
0
0
1
C
0
0
0
0
0
0
1
0
0
1
K
0
1
1
1
0
1
0
1
1
0
S
1
0
0
1
1
0
0
1
0
0
0
1
1
0
0
0
1
1
1
1
Frames
The diagram above shows the logical file structure on a tape (long pieces of plastic ribbon coated with
magnetic material). Parity checking is used as a measure of security, that is, to ensure that the
original data is not corrupt or missing in any way.
In the above diagram (which shows part of a tape ribbon), parity checking is even and this can be in both
horizontal (tracks) and/or vertical axis (frames). Check and count the bits for every frame and then for
every track. Parity can be even or odd.
If therefore the above file is transferred to a computer and if one single bit is wrong, then the parity will
no longer hold and the user gets an error display.
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Direct Access Method – Hard disk, Zip disk and floppy disk
Formatting a floppy disk or hard disk means preparing the medium to receive data. Mostly when a new
disk is bought, the surface are is free and not organized. In order to start writing data onto a disk, one
must format it or prepare the area into chunks where the data is stored (like boxes in a room to organise
our storage). Formatting prepares the disk into round concentric circles called TRACKS (like an athletics
track). Tracks are then subdivided into smaller pieces to form SECTORS. Even though the outer sector
is larger in area than the inner sectors, they will still hold the same amount of data.
Floppy disks rotate at about 360rpm. Data transfer is around 10k to 100k per second. They consist of
80 tracks and of 256 sectors per track. Floppy disks are lightweight, portable, relatively cheap,
rewritable, and can store 1.44Mb of data (they can store more if special software is used for compression
of data). Magnetic medium is brown in colour and soft. Disk allows random access. This is achieved
by storing each new file at the start of a new sector. If for example, program one occupies sectors 0, 1,
2 and half of sector 3, file two will be stored in sector 4, leaving half sector 3 empty. All programs stored
on disk are catalogued in a directory for easy searching. This is done by the operating system. A file is
not necessarily stored in sequential sectors but may be fragmented.
Hard disks are not readily portable (some exist which can be removed), becoming cheaper, rewritable,
typical storages nowadays at around 30GB (and more). Magnetic medium is shining silver metal and
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hard. Since hard disks are getting larger and larger an important factor to look at when buying a new
hard disk is its access time.
Zip disks are very popular for making backups both in the industry, offices and at home. They are
magnetic disks but the media is made of high density magnetic material – meaning that the surface is
more densely packed with magnetic particles. This allows for high density of data too. Zip disks use
special compression software which packs large amounts of data into smaller sized data. Zip disks
require special zip drives and special software compression. Typical zip disks are of 100Mb and 250Mb
capacities and are small cartridge like in shape.
Zip Drive
Zip Disk
Access time – the time taken for a hard disk to seek data and is measure in milliseconds (1/1000th of a
second). If you have a hard disk with an access time of 10ms, a file of 10Mb will take less than another
with 12ms to access. Typical access time (time to seek data) is between 9ms / 12ms, the lower the
access time the costlier. Hard disks usually consist of 2 or more similar disks mounted on a common
spindle, this is then known as stack.
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A stack is a number of rigid disks put on top of each other on a spindle or pivot. Files are accessed by
making reference not just to the track and sector but also on side number. Same track numbers on
different disks are known as cylinders. These were used on mainframe computers.
Direct Access Method – Optical Disks
This is the most promising secondary storage technology; optical storage involves the use of a high
power laser beam to burn microscopic spots off the aluminium disk’s surface coating. Data is
represented by the presence of holes along a smooth shining surface. Binary ‘0’, aluminium surface
burnt out presence of holes. Binary ‘1’, aluminium surface reflects back. A much lower power beam is
then used to retrieve the data. The patterns of spots detected by the laser during a read operation are
converted into electronic signals used by the computer.
The capacity of the optical disk is enormous compared with most magnetic disk storage devices. A 5.25”
optical disk, little larger in size than a diskette, can store between 600Mb to 17GB.
Standard Density
Double Density
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Quadruple Density
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CD-Rom (medium)
CD-Rom stands for Compact Disk Read Only Memory – note that these disks are for reading and only
store the information that the manufacturer records on it. The user cannot erase, change, or add to it,
only read it. This type of optical disk is used primarily for storing huge amounts of data – such as
government statistics, encyclopaedias, medical reference books, and dictionaries. CD-Rom’s have an
access time of about 160ms and a transfer rate of up to 800KB/s
The CD-Rom is an optical storage disk – meaning it can be read by light sensing equipment. The
difference between this and magnetic type storage is the large amount of data it can hold. In fact, a CDRom can store up to 600Mb of data. Unlike the hard disk it is portable. A CD-Rom allows manufacturers
to store video clips, still pictures and sound tracks apart from text to create what we now call multimedia.
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CD-R – WORM (medium)
WORM stand for Write Once Read Many
This type of video disk allows for recording onto the next free tracks until the disk is full.
This type of medium is recorded only once.
CD-RW – Erasable Optical Disks (medium)
Erasable optical disks are an alternative to large capacity hard disks. They store 1,400 times as much
data as diskettes. In contrast to CD-Rom’s, erasable disks can be modified and erased. The removable
disks provide convenience and security along with huge storage capacity. Optical disks can also be used
to back up fixed hard disks. Many experts think that optical storage will become the most efficient
inexpensive storage method. They offer 15,000 tpi (tracks per inch), compared to 96 tpi of floppy disks.
NOTE that although nowadays we have re-writable CD’s they are still not suitable for storing word
processing documents, databases etc. for they do not allow editing and manipulation (Save to CD cannot
be performed like to a floppy disk). They can only store an exact copy, which cannot be altered. Be
careful to exam questions regarding this.
DVD – Digital Video Disk (medium)
The DVD medium is similar to the CD-Rom disk. There are no visible differences except that the tracks
are more closely packed. Therefore there are more tracks on the DVD than on the CD-Rom disk. These
new disks allow far more storage than the previous CD-Rom and today are available with a capacity of
around 17GB. This large amount of storage enables the inclusion of more video clips; in fact, the most
significant development sector for the DVD is in the film industry. One can already rent full feature films
on DVD’s. The advantage of DVD’s over the original video cassette tapes is the high quality digital sound
and video. These films are sometimes also provided with different language tracks pre-recorded so one
can choose the language in which to listen to the sound track
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Optical Disk Drives
A CD-Rom is similar to an audio CD but with the recording tracks much thinner and closer to each other.
Therefore, the disk would be holding much more tracks for recording. At first there were two or three
major standards, which meant that not all CD-Rom drives were compatible to read all CD Rom’s.
However agreement was reached and a standard was set up. The CD-Rom drive uses a laser light to
read data on the tracks while the disk is spinning at a standard speed. These speeds have been
increasing rapidly from 1x to 40x. A high-speed CD-Rom drive, allows for better access time and better
refresh rates.
Access Time – the time taken for the transfer of data from the CD to the computer
Refresh Rates – higher refresh rates prevent the video picture from flickering.
DVD devices operate much on the same principle as CD-Rom drives. They use a laser light to trace the
video signal on the tracks. The tracks are however more compact and since the layout of these tracks is
totally different from that of the CD-Rom drive new standards had to be agreed.
Backing Storage Device, Media and Access Type
DEVICE
MEDIA
TYPE
ACCESS
Cassette Tape Drive
Cassette Tape
Magnetic
Serial
Reel to Reel Tape Drive
Reel Tape
Magnetic
Serial
Floppy Disk Drive
Floppy Disk
Magnetic
Direct
Hard Disk Drive
Hard Disk
Magnetic
Direct
Zip Drive
Zip Disk
Magnetic
Direct
CD-Rom Drive
CD-Rom
Optical
Direct
WORM Drive
WORM
Optical
Direct
CD-R, CD-RW
CD-R, CD-RW
Optical
Direct
DVD Drive
DVD
Optical
Direct
Flash Memory Unit
Flash Memory Card
Electronic
Direct
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BOOLEAN LOGIC
Computers are effectively complex calculators. All inputs to the computer from keyboard, mouse and
other input devices must be translated to numbers. This is done so that the computer would be able to
work out the problem and produce the required output.
The computer uses TWO numbers:
1 and 0
Discrete (Digital) and Continuous (Analogue) Data
Discrete data or digital data consists of a set of pulses, which may be counted. A switch can be
either on or off (1 or 0). Integer numbers are also discrete – you cannot have a whole number between
5 and 6 for example. Other examples of discrete data are car mileometer readings, heartbeats etc.
Modern computers can only store and process digital data. Hence any analogue data which needs to be
processed by a computer must be first converted to digital form. This is done by taking samples of the
analogue data at fixed time intervals. These samples are then converted to the digital equivalent.
Modems are used to convert analogue data to digital and vice versa.
Examples of Analogue type:-
Speedometer, Thermometer, Spring Balance
Examples of Digital type:-
Mileometer, Digital Thermometer, Pulse or Heartbeat Reading.
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Logic Gates
Logic gates are electronic devices that are used in the computer to work out these mathematical
calculations. Logic gates are fed with a particular binary number consisting of two or more digits and
generate a single output. Logic gates have rules which determine the output of a logic gate depending
on the input of the logic gate. These rules are known as truth tables.
In this course we are going to concentrate on three basic logic gates:
-
AND Gate
-
OR Gate
-
NOT Gate
What is a logic circuit?
A combination of logic gates which perform several logic functions such as:
-
control the flow of information
-
carry out arithmetic and logic (ALU) functions
-
help to store information and time operations
OR Gate
AND Gate
A
C
B
A
C
Input
Output
B
A
A
C
C
OR
B
NOT Gate
AND
B
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Input
Output
NOT
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Computer Studies
The OR Gate
The OR gate can be compared to an electric circuit consisting of a battery, a bulb which represents the
output, and two switches, switch A and switch B which represent the inputs connected as shown above.
Two inputs (A and B), when combined in an electrical circuit using an OR Logic Gate will yield an output
(C) which is equal to either 0 (false) or 1 (true), depending on which values, 0 or 1, the inputs have. In
general, OR is true when either or both inputs (A and B) are true, otherwise, OR is false.
The following truth table shows when an OR Logic Gate is true and when it is false.
Input A
Input B
Output C
1
1
1
1
0
1
0
1
1
0
0
0
The only time Output Y is true (equal to 1) is when either or both Inputs A and B are true (equal to 1);
when both Inputs A and B are false (equal to 0), Output Y is also false (equal to 0).
The AND Gate
The AND gate can be compared to an electric circuit consisting of a battery, a bulb which represents the
output, and two switches, switch A and switch B which represent the inputs connected as shown above.
Two inputs (A and B), when combined in an electrical circuit using an AND Logic Gate will yield an output
(C) which is equal to either 0 (false) or 1 (true), depending on which values, 0 or 1, the inputs have. In
general, AND is true only when both inputs (A and B) are true, otherwise, AND is false. (When
any Logic Gate is true, it means that electrical current is able to go through it; when it is false, electrical
current is not allowed to go through it.)
The following truth table shows when an AND Logic Gate is true and when it is false.
Input A
Input B
Output C
1
1
1
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1
0
0
0
1
0
0
0
0
The only time Output Y is true (equal to 1) is when Inputs A and B are both true (equal to 1), otherwise
Output Y is false (equal to 0).
The NOT Gate
The NOT Gate has only one input and one output as shown in the table before.
Whenever an Input is true (only one Input is required), the NOT makes it false. Similarly, whenever an
Input is false, the NOT makes it true. The NOT gate is also known as an inverter.
The following table shows when Output C is true and when it is false.
Input (A or B or Combination)
Output C
1
1
0
0
Output combinations VS Inputs
The amount of inputs to a logic gate will determine the number of possible outputs. This can be worked
out by following this simple calculation:
For “n” number of inputs to the gate, the combinations produced can be calculated by using 2n
-
Where ‘n’ stands for the number of inputs to the gate
-
Where 2 stands for the binary number that can have only two digits either 1 or 0
Example:
A gate with 2 inputs 22 = 4
A gate with 3 inputs 23 = 8
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A gate with 4 inputs 24 = 16
Etc….
Boolean Expressions
What is a Boolean expression?
• An expression which uses Boolean operators such as AND, NOT, OR.
• An expression that results in a value of either TRUE or FALSE
The logic circuits (diagrams) can be represented by using Boolean algebra.
When building the Boolean expression, the following symbols should be used at all times:
1)
A OR B represented as A + B
2)
A AND B represented as A.B
3)
NOT A represented as Ā
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Example:
A
NOT
X
B
AND
C
In order to work out a Boolean expression, one must follow some basic steps:
a. The Boolean expression is a representation of the logic circuit
b. The expression is the relation of the output with respect to the relative gate inputs
c.
Always work out the Boolean expression starting from output to the input
d. The logic circuit is made up from a number of gates, thus it is good practise to see the circuit as
being made up of a number of gates rather than as a whole
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- Practical Examples -
Example 1:
The figure below shows a logic circuit:
A
X
NOT
B
C
AND
a. Complete the truth table for:
A
B
X
C
0
0
1
0
0
1
1
1
1
0
0
0
1
1
0
0
b. Represent the logic circuit in Boolean algebra:
C = ((NOT A) AND B)
C = ((Ā) . B)
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The figure below helps to understand better how the Boolean expression above was constructed:
A
NOT
B
AND
C
C = ((Ā) . B)
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BINARY CONVERSIONS
Objectives:
1. Representation of numbers in binary
2. Conversion from Binary to Decimal and vice versa
3. Conversion from Hexadecimal to Decimal and vice versa
4. Conversion from Hexadecimal to Binary and vice versa
5. Perform Binary Arithmetic – addition and subtraction
6. Understand the concept of registers, complementation, ranges, left and right shifts
7. Numerical overflow
8. How to calculate number of bits required representing a number
9. Representation of negative numbers
10. Representation of characters – ASCII and EBCDIC
Number Systems
As discussed in the Boolean Logic chapter, the computer is basically a complex calculator. A computer
must translate everything to number form and perform a series of calculations before it can work out
something. It does not use the Decimal number system as us humans but uses Binary numbers and
Hexadecimal numbers. This chapter will help us to understand better how the conversions are made,
and how calculations are achieved.
Why Binary?
A computer, being an electronic machine is made up of switches, that is, the circuits are either in the ON
state or in the OFF state. The binary number system is the ideal number system to represent the twostates because it has only two digits: zero and one. A term commonly used to refer to 1 or 0 in binary
system is bit.
A bit is defined as a Binary Digit that can be either 0 or 1. A group of 8 bits is called a byte. The
number of bits processed by a processor is called the wordlength and is determined by the computer
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manufacturer. The following terms are often used as a unit of memory measure of a computer. For
example, we speak of gigabytes of hard-disk space and megabytes of RAM
•
A BIT (Binary Digit) is one of the digits used in binary notation, i.e. 0 or 1.
•
A BYTE is made up of 8 bits.
•
A KILOBYTE is 210 bytes = 1024 bytes.
•
A MEGABYTE is 210 Kilobytes = 1024 Kilobytes.
•
A GIGABYTE is 210 Megabytes = 1024 Megabytes.
Decimal or Denary system
As already mentioned, human beings use the Decimal number system to perform calculations. This
number system is based on the manipulation of 10 basic numbers
System
Base
Digits Used
Decimal
Base 10
0,1,2,3,4,5,6,7,8,9
Binary System
The computer is made up of electronic circuits, which in turn are made of switches. A switch can be
either ON or OFF, meaning it can only have TWO states.
System
Base
Digits Used
Binary
Base 2
0,1
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Hexadecimal System
Hexadecimal numbers are used by the computer for addressing the memory locations. Hexadecimal
system uses a 16-digit system
System
Base
Digits Used
Hexadecimal
Base 16
0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
As the Hexadecimal system has more digits than the Decimal system, letters had to be added to the
system:
A
=
10
B
=
11
C
=
12
D
=
13
E
=
14
F
=
15
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Decimal to Binary Conversion
In order to convert a Decimal number to Binary, we must divide the decimal number by 2 successively.
If the number has a remainder, this is equal to 1, if not it will equal to 0:
Example:
2
4
2
15
2
2
2
r0
2
7
1
r0
2
0
r1
2
ANS: 0010
2
48
r1
2
24
r0
3
r1
2
12
r0
1
r1
2
6
r0
0
r1
2
3
r0
2
1
r1
0
r1
ANS: 01111
ANS: 0110000
Most Significant Bit (MSB) and Least Significant Bit (LSB)
110101
Most
Significant
Bit
(MSB)
Least
Significant
Bit
(LSB)
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Binary to Decimal Conversion
1st Method:
Using a general formula to convert to decimal from any base:
(n x basex) + ..(n x base3) + (n x base2) + (n x base1) + (n x base0)
Example – For Binary system (Base 2):
Convert 11101 to Decimal
(1 x 24) + (1 x 23) + (1 x 22) + (1 x 21) + (1 x 20)
(1 x 16) + (1 x 8) + (1 x 4) + (0 x 2) + (1 x1)
16 + 8 + 4 + 0 + 1
=29
nd
2 Method:
Short method of conversion – by weight
Binary place value
27
26
25
24
23
22
21
20
Weight
128
64
32
16
8
4
2
1
Example – For Binary system (Base 2)
Convert 11101 to Decimal
1
1
1
0
1
16
8
4
2
1
16 + 8 + 4 + 0 + 1
=29
NOTE: In this method you only ADD where there is a Binary 1
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Convert from Decimal to Hexadecimal
1st Method – By Division
In this method, the decimal number is divided by 16. In this way a remainder from 0 to 15 is obtained.
You must keep in mind that in Hexadecimal we have to convert from 0 to 15 into A to F respectively.
Example:
16
30
16
1
r14
0
r1
ANS: 1
14
ANS: 1
E
16
100
16
6
0
ANS: 6
16
1024
r4
16
64
r0
r6
16
4
r0
0
r4
4
ANS: 4
0
0
2nd Method – By Grouping
In this method, one must first change the decimal number to binary. Secondly, the binary number must
be grouped in groups of 4 bits each, starting from the least significant bit.
Finally each individual group in converted to decimal again, and any number greater than 9 must be
converted to A to F.
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Example:
Convert from Decimal to HEX
Decimal Number:
166
Step 1:
Convert to Binary:
10100110
Step 2:
Group in 4 bit groups:
Step 3:
Change to decimal:
ANS:
1010 0110
10
6
A
6
Convert from Hexadecimal to Decimal
1st Method:
As used in Binary to Hexadecimal conversion we are going to use the same method. This can be shown
more clearly through the following example:
Convert A516 to Decimal
A516
= (A x 161)
+
(5 x 160)
= (10 x 16)
+
(5 x 1)
= 160
+
5
= 16510
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2nd Method:
The second method involves the Hexadecimal number being grouped. Secondly, each number is
converted to a 4-bit binary number. Thirdly, each 4-bit number is grouped in a single binary number and
finally this number is converted to decimal.
Convert B316 to Decimal
HEX Number:
B3
Step 1:
Divide into single numbers:
Step 2:
Convert each number to binary:
Step 3:
Regroup:
Step 4:
Convert to decimal:
B
3
1011
0011
10110011
17910
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Converting from Hexadecimal to Binary
Converting Hexadecimal numbers to Binary is relatively simple. One must first get each HEX number and
convert it into a 4-bit binary number. Finally, the individual 4-bit binary numbers are grouped together to
form a single binary digit.
Example:
Convert A4F16 to Binary
HEX Number:
A4F
Step 1:
Divide into single numbers:
Step 2:
Convert each number to binary:
Step 3:
Group together:
A
4
F
1010
0100
1111
1010010011112
Convert from Binary to Hexadecimal
Converting from Binary to Hexadecimal follows the same principle as used in the HEX to Binary
conversion. The Binary number is first divided into 4-bit binary groups. Each group is converted to
decimal and then finally to HEX.
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Example:
Convert 110011012 to Hexadecimal
Binary Number:
Step 1:
Divide into 4-bit groups:
Step 2:
Convert to decimal
Step 3:
Convert to HEX
11001101
1100
1101
12
13
C
D
= CD16
Binary Arithmetic
As mentioned before, the computer is a complex calculator and certain arithmetic calculations take place.
In this course we are going to concentrate on learning how to perform addition and subtraction on Binary
numbers.
Addition:
Since in Binary we only use two numbers; 1 and 0 calculations are very simple to understand. However,
some rules have to be followed:
0
0
1
1
+
+
+
+
0
1
0
1
=
=
=
=
0
1
1
0 carry1
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Example:
Add the following binary numbers:
1) 1101 + 1100
2) 1000 + 0111
Sum (1)
Sum (2)
Carry 1
1101 +
1100
11001
13
12
25
1000 +
0111
1111
8
7
15
Carry 1
Subtraction:
Subtraction is not as easy as addition, since computers are not capable to perform subtraction. For this
reason, we must use addition. Consider the following
Subtract X from Y
ADD (-X) to Y
=
=
Y–X
Y + (-X)
In the end the two above examples will give the same result. This concept is known as
COMPLIMENTATION. In order to assign a negative quantity to a binary number one must perform 1’s
and 2’s compliment.
1’s Compliment
In order to find the one’s compliment of a binary digit one must replace ones (1’s) with zero’s (0’s) and
vice versa.
Example:
Find the one’s compliment of 11001010
Binary digit
11001010
Convert
00110101
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2’s Compliment
To achieve the two’s compliment, you must add a binary 1to the one’s compliment of a binary number
Thus following the result obtained in the example above we have:
One’s compliment
ADD 1
00110101
+1
Two’s compliment
110110
Subtraction Rules
1. Arrange binary digits to have both the same length
2. Calculate 2’s compliment of number to be subtracted
3. Add this to the other binary number – ignore the carry number to keep the original size
Example:
Work out 110 – 11
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Computer Studies
Step 1:
110 – 011
110 + ( - 011 )
Step 2:- Find two’s compliment of the negative number
Number
1’s compliment
Add 1
011
100
+1
2’s compliment
101
Step 3:
110 +
101
1011
Ignore the carry so ANS is:
11
Registers
In our computer, information is held in the form of Binary digits and stored in Registers, these being like
binary containers or drawers. Registers have certain limits or sizes; in other words an 8-bit register
cannot contain a 6-bit binary digit.
A number that it is too big to be represented in a register of a particular size causes a Numerical
Overflow Error.
For Example:
A 3bit register is used to store the number 810
810 = 10002 – As it can be clearly seen you need 4 bits to represent the decimal number 8. In this case
an Overflow Error will be generated.
A Number overflow error can also be generated if the number is too small to be represented in the
register.
A register can contain integers, that is the quantity of a whole number. This whole number can be
positive, negative or zero.
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Unsigned Integers – can only be positive or zero. If we take a 3-Bit digit, we can have the following
numbers:
Example:
Binary
000
001
010
011
100
101
110
111
Integer
0
1
2
3
4
5
6
7
In order to determine how many different combinations or codes can be obtained using a number of
digits; one can use the expression 2n.
Example: How many different combinations can be obtained using 8 bits?
28 = 256 combinations
To determine the largest number that can be obtained using a number of bits one must use
2n - 1
Example: What is the largest number that can be represented using 8 bits?
28 - 1
256 – 1 = 255
We subtract one since the numbers start from zero. In this case the range is between 0 and 255
Thus, the larger the size of the register, the greater is the largest number that can be stored in it as
illustrated in the table below:
Size of register
2 bits
4 bits
8 bits
16 bits
Different codes
22 = 4
24 = 16
28 = 256
216 = 65536
Largest integer
4-1 = 3
16-1 = 15
256-1 = 255
65536-1 = 65535
Range
From 0 to
From 0 to
From 0 to
From 0 to
3
15
255
65535
Signed Integers
Signed integers are all those integer numbers that can be either Positive, Negative or Zero. Signed
integers can be represented as follows:
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•
Sign and Magnitude Representation
•
One’s Compliment Representation
•
Two’s Compliment Representation
One’s compliment and Two’s compliment were discussed earlier when we dealt with the binary
subtraction.
Sign and Magnitude representation
This mode has a bit after the most significant bit that shows if the number is positive or negative. When
this bit is 1, it is negative and when it is 0 it shows that it is positive.
Example: The 4-bit register in the example is representing -6
0
1
1
0
0 means Positive
1 means Negative
The Range of Signed Integers
In order to obtain the range of signed integers that can be represented in an X-bit register, the following
expression can be used:
- (2n-1) < x < + (2n-1 -1)
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Example: What is the range of signed integers that can be represented in a 4-bit register?
- (24-1 - 1) < x < + (24-1 - 1)
- (23 - 1) < x < + (23 - 1)
- (8 - 1) < x < + (8 - 1)
- (7) < x < + (7)
This shows that the range is between -7 to 7
Representation of characters
As we already know, all information going in the computer must be changed to binary numbers. Thus
each character must be assigned by a numerical code referred to as a Character Code.
The Character Set is the group of codes that can be used. The number of codes that can be created in
this character set is dependant on the size of the bits used to store the character.
Example: if an 8-bit is used, 256 (28) characters can be represented
There are two standards that are widely used:
-
ASCII Character Set
-
EBCDIC Character Set
Refer to page 368, 369 and 370 of your text book
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APPLICATION SOFTWARE
1.
Hardware and System software (Operating System) alone do not provide a single
specialised task
2.
Application Software is a type of software that performs task to directly benefit or
assist the user
3. Application Software is installed on top of an Operating System such as MS Windows.
The Operating System itself is NOT a type of Application Software
4
MS Windows is a popular Operating System on small computers. Windows provides an
easy interface between the computer and the user.
It uses pictures (graphical
representations) which look like ‘push buttons’ on the screen and the user can use the
mouse to select them. This interface idea is known as Graphical User Interface (GUI).
The following image shows the familiar GUI of MS Windows XP
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Definition of Application Software:
A complete system for a particular application supplied by an external body or written in-house, for
general use by individual installations using their own data.
Application Software Examples:
1. Word Processing
2. Spreadsheets
3. Databases
4. Accounting
5. Games
6. Internet Browser
7. Desktop Publishing
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Different Application Software:
APPLICATIONS SOFTWARE
Productivity
Software
Word processing
Business
Specialty
Software
Desktop
publishing
Spreadsheets
Personal finance
Presentation
Graphics
Entertainment
Software
Home /
Personal
Software
Games
Cookbooks
Etc..
Medical
Encyclopedias
guides
Almanacs
CAD / CAM
Gardening
Library searches
Etc..
Home repair
Painting
Etc..
Communications
Hypertext
Groupware
Multimedia
authoring
(and multimedia
software
components such
as animation
software,
music/MIDI,
sound capture
and editing, video
capture
and
editing,
speech
synthesis,
drawing, painting,
hardware support
)
Browsers
books
Home decoration
Drawing
Suites
Phone
Project
management
Database
managers
Desktop
accessories
Education /
Reference
Software
Off the shelf and Custom made Application Software
The Application software can either be bought off the shelf or else custom made to the buyers’
needs.
Off the shelf:
Are the ones we find in the computer shops developed by large software houses, made
for the general user. Since the market for such software is larger, the price is lower.
Custom made:
These are designed to meet the buyers’ needs and specifications, and can be guaranteed
to full fill all the functions required by the customer.
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Advantages and Disadvantages of buying off the shelf software
Advantages / Benefits (ref to book pg 277):
1. Cheaper in price.
A wider market is reached; more people are ready to buy the software
2. Quicker and less costly implementation.
Can be performed by the user, implementation is simple and doesn’t require
knowledge on the software
3. Greater system efficiency.
The software would be fully compatible with the operating system
4. Proven and tested.
Tested thoroughly by a specialized team
5. Documentation provided with the package
Reliable documentation that can help the user to install and operate the software
6. Changes automatically catered for by the supplier
The different options to change settings are provided by the software manufacturer
7. User friendly
Simple, easy to understand and to use
Disadvantages / Reluctance:
1. Processing logic does not always fit the true situation of the hardware, requirements are
difficult to meet
Examples of requirements that are hard to meet:
Hard disk space – Not large enough, and not enough RAM
2. Too ‘Generic’, might have to change present procedure to accommodate the package
(Should be vice versa)
Due to the limitations offered by this type of software, it might be needed to adopt
the present procedures to the software. This can be very stressful for the user and
thus prone to errors.
3. The package is not efficient in certain aspects (some information irrelevant to
the environment).
Since the software is not designed on the specific environment that is going to be
used in, some functions will not be efficient. An example would be Payroll
software.
4. Integration with other packages could be very difficult or impossible.
The newly installed software might create some problems with other applications
(Conflict).
User – Friendly (ref book pg 278)
User friendly software goes beyond simply performing the data-processing tasks required by the
application. The software application will be designed to make the life of the user easier when
using it.
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Some features of a user friendly software:
i.
Easy to use:
Lets the user do the job with minimum effort
ii.
Robust:
Application should be tolerant to user’s mistakes and allow recovery if
something should go wrong.
iii.
Attractive and ergonomically designed:
Attractive screen layouts and colours; Ergonomically designed: Working
in a way the user finds it natural and comfortable.
iv.
Helpful:
If a mistake is done, the application should give the user a clear
explanation of what was wrong and how to recover from the error.
The system should issue warning messages and request confirmation
before allowing the user to proceed.
On-line help, through telephone line or through Internet.
One should not underestimate the importance of user-friendliness for the
success of a system – all too often a computer system does not succeed
simply because users do not accept it.
Integrated packages (ref book pg 279)
Care should be taken that application software would be fully compatible. To eliminate the risk
of incompatibility is to purchase an ‘Integrated package’.
An Integrated package is a package of different application software such as Word Processors
and Spreadsheets but with reduced functions. Examples of application software packages are
‘Microsoft Works’ and ‘Lotus Works’. This kind of application software costs less and takes less
space on the hard disk.
Another solution for incompatibility is to purchase a ‘Suit of applications’ such as
‘Microsoft Office’.
This type of package would be made up of different full applications software. These cost more
than the integrated software package, but less if you had to buy the applications one by one.
Takes more space on the hard disk, for example MS Office 2003 takes about 400Mb of hard disk
space.
Applications of Information Technology Common to most Organizations (ref book pg
279)
Certain computer applications and information systems are universal and equally appropriate for
different companies.
Payroll
1. Payroll software mainly deals with salaries, tax and National Insurance of the employees.
2. The two primary outputs of a payroll system are cheques or payslips.
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Accounts
1.
The accounting package keeps track of money owed to the company for goods sold or
services provided.
2. Production and updates of invoices, bills and statements.
3. The accounts payable systems is the other side of the accounts functions.
4. Monetary transaction that occurs within an organization must be properly recorded
(transfer of funds).
5. This kind of application software provides financial statement, which includes the profit
and loss statement and the balance sheet.
Inventory Management and Control
1.
A fixed-asset inventory record is maintained for each item and includes such data as date
purchased, cost, location, and inventory item number.
2. These records are maintained for asset-control and tax purposes.
3. Inventory systems monitor the quantity on hand and the location of each item. Such a
system will monitor and help eliminate stock outs (out of stock) and over stocking of raw
materials.
Human Resource Development
1.
Human resource development systems maintain data on employees, such as educational
background and salary history
2. The system includes data on performance reviews, skills, and professional development.
Manufacturing
1. In a manufacturing company, the order entry and processing system accepts and processes
customer orders.
2. When an order is made, the system takes care to feed data, either to the warehouse if the
item is in stock or if it is out of production. It also feeds data to the accounts receivable
system for billing.
3. The system monitors the orders from the order entry until the product is delivered to the
customer.
Production scheduling
Manufacturing resources (materials, machinery and workers) are allocated through the
production process in order to minimise time and increase efficiency of the production line.
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Project Management
1. This application software provides the management with a tool to keep projection within
budget and on time.
2. The tasks, which are going to make up the project, are put one after each other in their
order so that the project can be finished.
3. This software will give the management a tool to plan the project without involving any
expensive measures.
Robotics
1. An industrial robot is best at tasks that are repetitive and tasks that require precision
movements, moving heavy loads, and working in hazardous areas.
2. This software application will give access to the robot programmer to load the set of tasks
that the robot has to perform to carry out the job.
Computer Integrated Manufacturing
The integration of computers and manufacturing is called Computer Integrated Manufacturing
(CIM).
The process usually follows these steps:
1. An engineer uses a Computer-Aided Design (CAD) system to design the part.
2. The design specifications are produced and stored on magnetic disk.
3. The specifications, now in an electronic database, become input to another computer
system that generates programs to control the robots and machine tools that handle and
make the part.
4. The tools provide data for order processing, inventory management, shop floor
scheduling, and general accounting.
Some computer – integrated manufacturing systems go one step further and provide a link
between the manufacturer and the customer via electronic data interchange.
Word processors (ref book pg 282)
A WORD PROCESSOR is a program, which is used for preparing documents, typing letters, and
producing reports.
Advantages of word processors over traditional typewriters:
Ease of correction
Automatic Formatting
Multiple copies and Form Letters
Automatic Features
Search and replace facilities
Spelling checkers and thesaurus
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Font changes
Mail Merge
Other features: Multi column text, grammar checker, table formatting,
inclusion of drawings
Desk top publishing (ref book pg 284)
Desk Top Publishing (DTP), involves using a computer, mouse, scanner, printer and Desk Top
Publishing application software for mixing text and graphics to produce high quality printed
output for commercial printing. The emphasis is not on the entry of text (as it is with wordprocessing), but the ability to compose text and format the document in a manner that comes
close to the quality achieved with professional typesetting equipment.
Desktop Publishing Software is used for:
Catalogues
Brochures
Presentations
Reports
Desktop Publishing Software is NOT used for:
Memos
News releases
Addressing
Mailing list
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DTP software must offer the following capabilities:
Allow high – quality composition of text:
The results must be of typeset quality, meaning that proportional spacing, kerning, tracking
and leading control, and justification of both right and left margins is possible. Automatic
hyphenation is also usually supported.
Support page composition:
This allows the user to arrange text and images on the display screen as desired – in columns,
sidebars, and so on. The arrangement on the screen is the same as that which appears when
the page is printed.
Incorporate graphics:
This makes it possible for the user to move text and images as desired. The DTP software
does not usually allow the user to create the text and the image data – these must be created
using other software (a word processor for the text, and a graphics package for the graphics)
and then imported into the DTP program for exact placement.
Provide editing capabilities:
All DTP software allows the user to edit text. Such text editing facilities are usually minimal,
and only meant for performing small corrections or adding captions and headings.
Printed results should be of high quality:
Although this of course depends more on the printer than the DTP software, it does mean that
the software must support high-resolution printers (typically at least 300 dpi resolution).
<< NOTE >>
Nowadays, Word Processors such as MS Word will also provide desktop publishing features such as
automatic table of contents and index creation, multi-column documents, tables, frames, embedded
graphics objects etc.
Even providing such DTP features however, software such as MS Word still is considered a Word
Processor and not a Desktop Publisher.
Spread sheets (ref book pg 285)
An electronic spreadsheet is a tool for performing calculations on data. Used generally for
accounting purposes, the spreadsheet is made up of columns and rows.
By using a spreadsheet program, one is able to automatically recalculate a whole sheet of figures
every time a single value is altered.
1. Components of a spreadsheet.
As mentioned earlier, the spreadsheet is made up of columns labelled with letters (A to Z, AA to
AZ, BA to BZ etc.) and rows labelled with numbers.
The intersection of a column and a row is called a CELL. Each cell has an address or coordinates for (e.g. A1, B6, F17, etc.)
2. Labels, Values and Formulas.
In each cell, the user may insert one of three types of items – LABELS, VALUES and
FORMULAS (or FORMULAE). The following example spreadsheet will be used for illustration.
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Lables are words to describe particular items such as Bread, Tomatoes, Meat etc.
Values are numeric quantities like LM 0.15, LM 0.30 etc. Value cells are sometimes called Input
cells, since the user inputs data to the spreadsheet via these cells, and represent the variables
or parameters of the system being modelled by the spreadsheet.
Formulas describe computations to be made on the contents of the cells (formulas are not
displayed on the spreadsheet – they are computed, and their results displayed instead). For this
reason, formula cells are sometimes called Output cells or Result cells, since they serve to
display the results of computations performed by the spreadsheet.
The real power of a spreadsheet comes from the fact that formulas are recalculated every
time the value in a value cell changes – the output cells change dynamically as the input
parameters are varied.
Spreadsheet formulas can perform:
I.
II.
III.
IV.
Financial calculations
Mathematics
Statistics
Date calculations
3. Operations on Cell.
Spreadsheets can carry operations on cells or group of cells such as: clear, move, delete and
copy whole rows and columns.
4. Data Graphing.
A nice feature of spreadsheets is to display selected values in graphical form:
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Line graphs
Bar graphs
Scatter plots
Area graphs
5. Spreadsheet publishing.
Modern spreadsheets support desktop publishing features such as fonts, colours, graphics and
borders. These features are useful for preparing presentation and reports.
Database systems (ref book pg 288)
Databases are typically used for storing and accessing data.
A Database can be simply defined as a collection of information that is organized so that
it can easily be accessed, managed, and updated.
Basic terminology used in Database environments:
Record:
A structured collection of data regarding a single person, and is composed of fields. By structured
we mean that, for example, an employee’s record is not just a haphazard collection of facts and
figures, but is a form which entries for the employee’s name, number, address, rank and any other
item of data thought desirable for record purposes.
Fields:
A field holds a single item of information about that individual (for example: name, surname,
address etc.)
Fields come in various types, depending on the type of data to be stored. Some common field types
are:
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a.
Numeric
b.
Date fields
c.
Logical fields (or Boolean fields)
d.
Text fields
e.
Memo fields
f.
Picture fields
Note: for more information on fields, follow text book page 289
The Database Management systems (ref book pg 289)
The Data Base Management Systems (DBMS) is a software package for creating, maintaining and
retrieving data from a database.
Although the term database is frequently taken to include BOTH the collection of data AND the
package which provides access to the data (the DBMS), strictly speaking this is not so. We will use
the following terms for clarity:
Database:
A collection of data in the form of records.
DBMS:
The software which manages a database. It may include custom written
applications.
Database System:
The combination of application software (perhaps written using the
DBMS itself) and the data on which it operates.
Facilities offered by a database system include:
1. Creating the database
2. Updating records
3. Retrieval of data
4. Reduction of data
Data Integrity
In order to minimise the chances of inputting the wrong data in the Database, the database
software must be required to perform integrity checks whenever an update operation is attempted.
Such checks may involve:
Type checking:
The DBMS will ensure that only the appropriate type of
data is entered in a field – e.g. only numbers in a numeric field, only dates in a date field,
and only Y / N entry in a logical field.
Range checking:
The DBMS may be instructed to only accept values within a
certain range for a numeric or date field – for example the DBMS may reject a date of birth
which is less than 16 years ago or more than 61 years ago, or a PAYE rate less than 0 or
more than 35
Limited options:
This is similar to range checking, but is usually applicable
only to textual data. The DBMS can be instructed to accept only a value from a limited
set of possible values. For example, only village / city names from a predefined list may
be acceptable in an address field.
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When a value entered in such a field, the DBMS can immediately check that the value
entered is in the list, and if not reject it. This practically eliminates mistyping such fields.
Required fields:
While certain fields may not apply in certain cases (e.g.
telephone number) and therefore may be left blank, others are required (e.g. an
employee number and employee name). The DBMS will ensure that required fields are
not left blank.
Mutually dependant fields: Certain fields may depend on other fields. For example in
a record, which contained fields MARRIED and WIFE’S NAME, entering ‘N’ for the first
should force you to leave the second blank, and vice versa. The DBMS may be instructed
to carry out such checks.
Unique fields:
Certain fields may be declared unique, such as the
employee number field. Such fields are called key fields, and serve to uniquely identify a
record. The DBMS can ensure that data entered in such fields is indeed unique.
Data Retrieval (ref book pg 291)
Databases are quite useless unless one can retrieve the stored data. Asking the DBMS to fetch
data from the database is called querying the database.
Some databases have Query language (e.g. SQL); a simple English like language for
describing what data is needed from the database.
Others support Query By Example (QBE), in which you give an example of what you need by
partially filling in a blank record and letting the DBMS find all the records matching your example.
QBE tends to be simpler, but less versatile, than using a query language.
Report generation is a special form of querying, in which the output of the query, which can
include data grouping, subtotals and totals are printed out in the form of a report.
Data Security (ref book pg 291)
Database security involves 2 issues:
1. Ensuring confidentiality (or Protection of Privacy):
This can be achieved by assigning database users’ selective access. That is what
users can view from the database. Thus the user is given selective access to
the database on a NEED TO KNOW basis. The user’s view of the database is
restricted to only those fields in each record to which they have access.
2. Protection against damage:
This can be achieved by assigning what users can and cannot change from the
data. This is called an access type. Distinction is commonly made between
authorisation to read (view) and authorisation to write (change) – someone may
be granted access to 5 fields in a database, but only granted permission to
change 2 of those fields – the others may be viewed but not altered.
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Simulations (ref book pg 292)
Computer Simulated Train
Computer simulations are useful scientific and business tools. They enable computers to
pretend (simulate) that they are carrying out a number of things from simulating a queue at the
post office, to working out what would happen in the event of a nuclear war.
Computer simulations are usually based on mathematical models held inside the computer
that represent the physical process being carried out in the real world.
Virtual reality simulations are different from computer simulations because they require
special interface devices that transmit the sight, sound and sensations of the simulated world to
the user.
Interface devices include:
Head mounted display (HMD), equipped with screens directed to the eye for the
vision, earphones for the sound, and position tracker to monitor the location of the
user.
The haptic interface (Haptic technology, technology that interfaces with the user through
the sense of touch), which relays the sense of touch and other physical sensations in
the virtual world.
Uses of Virtual Reality:
Virtual reality is currently used to explore and manipulate experimental data in ways that were
not possible before.
Therapists use VR to treat sufferers of child abuse and people who are afraid of heights.
Muscular dystrophy patients can learn how to use a wheelchair through virtual reality.
Surgeons may use VR to plan and practise an operation on a virtual patient rather than a
real person.
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Architects could take clients on a virtual tour of a new house before it was built.
VR could be used to train the operators of aircraft and other complicated machinery.
Network VR simulations could enable people in many different locations to participate
together in teleconferences, virtual surgical operations, or simulated military training
exercises.
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THE INTERNET
Objectives
To understand the nature of the Internet as in terms of a global network of computers
connected together.
Discover the different uses of the Internet such as email, information, browsing, file
transfer, socialising, and the use of other computers on the net.
Discuss HTML and URL and their uses in the world of the Internet.
The Internet ‘What is it?’ (ref book pg 395)
In order to understand the nature of the Internet, one must have a basic knowledge of
networking.
Networks is the term used when a number of computers are connected together in order
to share resources and achieve communication from one place to another.
LANs (Local Area Networks) as they are generally called are a network of computers that
cover a small geographical area – usually only the building of the company.
The internet can be described as a global network of computer networks. These networks
vary in nature and size, such as, huge government departments, university and college
networks, large companies such as IBM and many other commercial systems and non
profitable organizations.
People use the internet for different reasons such as, email, file transfer, information
retrieval, social chatting, and checking on news, weather etc.
In 1969 the USA government started a project called DARPA in order to connect
computers that are geographically distant from each other. This was required as a means
of exchanging military research information between researchers at different locations.
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By time, this network started evolving both in number and technology and in 1990 the
Internet that we know today was launched.
Today, the Internet connects millions of computers together that share resources and
knowledge.
The Uses of the Internet:
The use of the internet can be divided into the following five major categories:
1. The Email (Electronic Mail)
Probably the most common use of the internet. Email is much faster than traditional
methods of sending documents (postal system). Documents travel as binary files and
are then converted back into plain text using special software. Email is efficient and
convenient.
The email provides the facility to send letters through the Internet to people who have
access to the net. Multiple copies can be sent to multiple addresses just by adding the
address to the address list.
You can check for post at any time of day.
This is achieved by means of special application software such as Microsoft Outlook Express
or Netscape Communicator.
One of the greatest features of emails is the ability of attaching files to the letter in the
form of documents, pictures, sounds, and movies.
2. Information Browsing
One of the most used features of the Internet is to search for particular information through
large databases all over the world
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This information provided in the form of web sites makes part of the so – called World
Wide Web or more commonly known as WWW. This is a means to search information
centres all over the world.
Examples of software used to access the WWW are MS Internet Explorer and the Mozilla
Firefox
3. File Transfer
FTP or File Transfer Protocol is a system used on the Internet to make possible the
transfer of information from one computer or network to another.
Anonymous FTP refers to those archive sites which allow anyone to access it.
4. Socializing – Chat and Newsgroups
An important part of the Internet which is widely used by youngsters is the Chat or
Internet Relay Chat – IRC. With this facility, people can communicate real – time
through the keyboard.
Another form of socialising, are newsgroups (known as Usenet). This allows you to post
and read articles on newsgroups. Usually newsgroups are grouped and have a particular
topic
.
5. HTML – Hypertext Mark-up Language
HTML is a language that is used to create Web – Sites. This language gives the facility of
linking different pages together.
On web – sites this can be seen when the cursor is dragged over a particular word or
phrase. The cursor will change from an arrow sign to a palm sign. When the mouse
button is double clicked on that word or phrase, another page will be loaded.
6. URL – Universal Resource Locator
This is the address that shows in which computer (information centre) the web – site is
held.
An Internet address (for example, http://www.4sale.com/trade/), usually consisting of
the access protocol (http), the domain name (www.4sale.com), and optionally the path
to a file or resource residing on that server (trade).
7. Study Note
In this chapter we have gone through the basics sections that make up the Internet. We have
also included some hints on how to send / receive emails and the basic steps for using Browsing
software.
At this point, you should be able to:
Understand the nature of the Internet as in terms of a global network of computers
connected together.
Understand the different uses of the Internet such as Email, Information browsing, File
transfer, Socializing and the use of other computers on the net.
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Describe HTML and URL and their uses in the world of the Internet.
Describe the basic features of the email and browsing software.
8. << Questions >>
Q1. What are the advantages of the email as compared to the conventional written letter?
Q2. Describe the term URL
Q3. How can the Internet promote socializing between people of different countries and
cultures?
9. Glossary
ANSI
American National Standards Institute
Anonymous FTP
Allows user to download files from a site
ASCII
American Standard Code for Information Interchange
Com
A code is ms-dos that refers to a serial port
DNS
Domain name system is a database system for translating computer
domain names into numeric internet addresses.
E-mail
Electronic mail, a method of sending messages via the computer instead
of post.
Encryption
A method of coding data to prevent unauthorised access
Ethernet
A type of high speed local area network
File Server
A computer that stores files on the Internet, making them available for
access by various internet tools.
Firewall
A security device to help protect a private network from internet hackers.
It’s a machine with two network interfaces that is configured to restrict
what protocols can be used across the boundaries and to decide what
internal IP addresses can be seen to the external internet.
Forum
A message area, where messages are left and seen
Frame
A block of data with header and trailer information attached
FTP
File transfer protocol, this defines how the files are transferred over the
internet.
HTTP
Hypertext Transport Protocol
HTML
Hypertext Mark-Up Language
Hub
A device connected to many other devices
Hz
Hertz – one cycle per second
IP
Internet Protocol
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IRC
International Relay Chat – allows many users to chat in real time
worldwide.
ISDN
Integrated Services Digital Network combines voice and digital network
services in one medium.
Log
A record of file operations
Login
The process of identifying yourself on an online system. Generally a two
part action, first the input of your username followed by your password.
Mailing List
A discussion group whose messages are distributed by email
Net Surfer
Someone who ‘surfs’ the internet, wondering around looking for
something of interest to visit
Newsgroup
Message area, defined by subject matter, which forms part of the Usenet
Node
A computer attached to a network
Offline
Not connected to an online system
PPP
Point – to – Point protocol, allows the computer to use TCP/IP over
standard telephone lines
Site
Any of the individual networks that as a whole comprise the internet
SMTP
Simple Mail Transfer Protocol – used to transfer email between
computers as part of the TCP/IP protocol family.
URL
Uniform Resource Locator, an attempt to standardise the location or
address details of internet resources, commonly used on the WWW.
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MULTIMEDIA
1. Objectives
What does the word Multimedia mean;
Basic hardware and software requirements;
Benefits of Multimedia;
Where it is used.
2. Multimedia
Definition of Multimedia:
Multimedia is a general term applied to all hardware devices and software that
offer a combined solution to video, audio and text presentations. The
presentations are usually interactive, which mean that the user may take an
active part in selection. This is the most active developing field for peripherals
and software alike.
The elements that make up a multimedia product therefore include:
- Video
- Audio
- Text
- Graphics and still picture
- Animation
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If a product contains at least three of these elements, it can be claimed to have multimedia
properties, but if no sound or moving pictures are present, then the benefits that can be obtained
from using it are limited.
3. Multimedia technology
Multimedia technology can be subdivided into 2 categories:
a. Multimedia Hardware and Software
b. The Transport and storage medium
4. Multimedia Hardware and Software
Most PC’s (Personal Computers) today are equipped with hardware that can support
Multimedia products (application software).
However, the minimum requirements by multimedia products are:
Operating system – MS Windows 95 or 98
CPU – 486DX2 / 66Mhz
RAM – 12MB for Windows 95 and 16MB for Windows 98
Screen display – 640 x 480 pixels, 256 colours
CD-Rom Speed – Double speed (2x)
Hard disk space – 6MB
Audio – 8-bit sound card
Other – Speakers or headphones and a mouse
As you can see, the minimum requirements shown above are way below what is available
in many computers today.
5. The transport and storage media
Multimedia products (software) are stored in digital formats. The standard media for the
storage and transport of Multimedia software has become the CD-ROM and more
recently the DVD-ROM.
The reason for adopting such a standard was for the excellent features that the CD and
DVD can offer. Such features are slim and portable size and have great storage capacity.
6. Benefits of Multimedia
There is an old Chinese proverb that says:
“I listen and I forget
I see and I remember
I do and I learn”
This proverb clearly and concisely explains the benefits of Multimedia products.
Apart from the motivation created by the sound and vision powerful presentations, most
multimedia products are interactive, thus the user is involved in the activity carried out
by the program.
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7. Where is multimedia used?
There are three main targets where multimedia is used:
A.> Businesses
Businesses are multimedia products for the staff training programs and for public information
systems or Kiosks.
B.> Entertainment for home and leisure use
Multimedia products today are being used for leisure products. These can vary from:
- Games;
- DVD’s on PC
- Interactive TV
C.> Education
Encyclopedias and books on CD-ROMs are becoming a common asset to find in modern homes.
Apart from these, you can also find programs with multimedia features designed to teach a
particular school subject to students.
Examples of application software and places where multimedia is widely used:
- The Internet (WWW)
- Office application software such as PowerPoint, FrontPage, and MS Word.
- Encarta Encyclopedia
8. Study Note:
In this chapter we have discussed the meaning of the word multimedia and the basic
powerful presentation features that this can offer.
We have also discussed the basic software, hardware requirements for the good
functioning of multimedia products and the storage / transport media used.
Finally, we have mentioned the three main areas where this technology is being used,
and we have also seen some practical examples that we use every day.
9. << Questions >>
Q1. Write a short essay of about 300 words describing the basic features of multimedia and what
you think multimedia can offer in the near future (10 – 15 years from today).
Q2. Select a multimedia product that you use on your PC and describe what makes it so
interesting.
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SOFTWARE
1. Objectives
What is software and why it is needed;
The difference between Application software and System software;
Installing computer System software and Application software;
Discuss the purchasing of software and software piracy and protection;
Nature of software;
Discuss System software, Control programs, Operating Systems, System utilities, Diagnostics
and program software.
2. Software
A computer system is made up of the hardware (physical electronics in or attached to
the computer caser) and the software (a program made up of instructions that tell the
hardware what to do);
Software programs can be divided into two main groups:
- Application Software
- System Software (refer to figure on page 267)
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The main job of the System software or Operating system as it is normally called,
deals with the control of the computer hardware whilst the Application software caters
for particular applications such as Payroll, Stock control, Word processor etc.
In order to run an Application software, an Operating system must be loaded first.
3. Installing a computer Operating system
To install an OS, it is recommended to backup or take a copy of the contents, if any, of
your hard disk since the hard disk is usually formatted prior to the OS installation.
This procedure can be dangerous, since if it is not performed as it should be, precious data
can be lost. It is thus advised that the installation documentation be read carefully.
Otherwise, it is best to seek help from a professional. Usually, the installation of new
operating systems like Windows has a friendly installation wizard that will guide you
through the process of loading.
4. Application Software
In order to install the Application Software, it is necessary to have an Operating System
previously installed;
Most modern application software comes on a CD or DVD. Installing a program is not
simply done by copying the contents of the CD onto the hard disk.
In order to perform the program installation one usually needs to run the installer or setup program usually present. This program provides an interface and guides you step by
step on how to install the program.
In the progress, program files might be uncompressed, put into their correct sub
directories, and the system configured for usage.
If a problem with the installation should arise, you should consult the installation manuals
provided with the software.
5. Buying Software
There are a number of benefits when buying original software:
It ensures that you have the latest version, including manuals and all accompanying
support material;
You can be given help from the manufacturer if you have trouble;
Upgrades at reduced prices;
It is requested by law that you only purchase licensed software (refer to book ‘The
software Copyright Law’ page 273);
Reduces virus risks.
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6. What is software piracy?
a. Industrial Piracy – Occurs when an individual attempts duplication and distribution on a
large scale for profit.
b. Corporate Piracy – This occurs when a copy of a single / one user licensed software is
installed on a LAN server and many people connected to the network can have access to
and use this software.
c.
Reseller Piracy – This occurs when computer hardware companies or shops sell
computers which are pre-installed with non-licensed software.
d. Home Piracy – An example of this form of piracy is the trading of copied software with
friends.
Please read the first paragraph on book page 270 so as to have an idea of the amount of
software piracy that takes place in Malta and the rest of the world.
7. Software protection
In order to produce software, software manufacturing companies spend a lot of money
and resources for producing that software;
Thus they adopt different systems in order to prevent their software from being copied
illegally;
Hereunder are some of the most commonly adopted protection systems (refer to book pg
270);
a. Security lock or Dongles:
These are hardware devices that are physically attached to the ports of the
computer. Before running, the software will check if the dongle is present. If it
is not present the software will be useless.
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b. Keyword protection:
This is frequently used with cheap software.
This system demands that every time you start the program, the software will
ask you to enter a particular word from the user’s manual. Each time the
program is used, a different word from a different page will be demanded.
Although it is quite easy to photocopy the manual, it is frequently not worth it
since the software is quite cheap (and the manual usually quite thick).
c. Software Registration:
The software owner will be asked to register the newly purchased software with
the manufacturing company. This can be achieved by either sending a card
supplied with the software by post, or by doing an on-line registration on the
Internet. Your name and details will be listed at the mother company’s database,
and thus this will give you some privileges, such as free help, cheap
upgrades etc.
d. Key Disk Protection:
The software disk will be formatted in a way that it cannot be copied. Every time
you attempt to run the program, the software will ask you to insert the Key Disk
in order to continue. This protection scheme isn’t very popular, because people
who buy original software like to take a backup as a precaution.
8. The Software Copyright Law
Basically, this is the section of law that explains the consequences of copying software illegally
(refer book page 271 and 273).
It is very important to check what type of software you are buying.
(Refer to book page 271 – 1.9 & 1.10)
9. Nature of Software
The term SOFTWARE includes all programs that control the computer’s activities. These are:
Programming Software
System Software
Operating Software
Application Software
Applied to solve particular
problems
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Systems Software:
All those programs which manage the functioning of a computer
system and help the application software to run. It does not solve end-user problems. It
enables users to make efficient use of the computing facilities for solving their problems. These
manage the resources of a computer system, automate its operation and make easier, the
writing, testing and debugging of user’s programs.
Control Programs:
This is an integral part of the operating system, which handles the
transfer of data between peripherals and internal storage, checks if peripherals are working
properly and informs the operator if they are not. Control programs together with the Operating
system fall under the Operating Software category.
The Operating System:
Is the combination of the system software and the control
programs. The operating system uses the power of the computer to minimise human
intervention. It manages jobs (program suites) handled by the machine, organises its program
of work and maximises the throughput of jobs. An operating system can provide specialised
facilities.
System Utilities:
These programs are included within the operating system. They
perform housekeeping tasks, such as formatting disks, backing up data and copying files, setting
system parameters etc. (Example – Windows Explorer).
Diagnostic Utilities:
These utilities perform hardware tests on particular devices to
check if they are working correctly. Diagnostic programs, usually supplied by the computer
manufacturer, perform hardware tests on specific components or devices, like testing of a parallel
port, memory integrity or hard disk defects and data corruption on files. (Example - Scandisk).
Programming Software:
These include all those programming tools necessary to create
(code) programs (usually application software).
These programs allow:
The writing of a source program file (using an editor)
Translation of source code into machine code
Production of the object program file
Testing and debugging aids
Program executor
10. Study Note
At this stage you should be able to discuss:
What is software and why it is needed;
The difference between Application software and System software;
How to install computer System software and Application software;
Discuss the purchasing of software and software piracy and protection;
Nature software;
Discuss System software, Control programs, Operating Systems, System Utilities,
Diagnostics and Programs software.
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