Contents
Section 1: Fundamentals of Hardware and Software ................................................................................ 1
Objective 1.1: Describe a general-purpose computer system.................................................................. 1
Objective 1.2: Explain the functions of the major hardware components of a computer system. ......... 2
Objective 1.3: Outline the functions and uses of primary storage devices. ............................................. 4
Objective 1.4: Manipulate units of storage. ............................................................................................. 5
Objective 1.5: Compare the types of secondary storage media w.r.t. portability, speed and capacity... 6
Objective 1.6: Use terms associated with storage devices. ...................................................................... 6
Objective 1.7: Explain the uses of various input devices and media ...................................................... 15
Objective 1.8: State the types and functions of output devices. ............................................................ 20
Objective 1.9: Describe how data are stored and manipulated within the computer. .......................... 25
Objective 1.10: Interpret the hardware specifications of a computer system. ...................................... 33
Objective 1.11: Distinguish between system programs and application programs. .............................. 35
Objective 1.12: Explain the functions of the Operating Systems. .......................................................... 38
Objective 1.13: Distinguish among multitasking, multiprocessing and multiprogramming. ................. 38
Objective 1.14: Explain the different types of processing modes. ......................................................... 39
Objective 1.15: Distinguish between types of user interface. ................................................................ 40
Section 1:
Fundamentals of Hardware and Software
Objective 1.1: Describe a general-purpose computer system.
Content:
Major functions of systems: input, processing, output, storage
Notes: The major functions of a general-purpose system
The major functions of a general-purpose system are:

Input: involves obtaining data for processing
1



Processing: involves the manipulation of data to produce information. Manipulation
means multiplying, adding, subtracting, dividing, sorting etc.
Output: involves sending information to users.
Storage: involves keeping the data on electronic storage.
Objective 1.2: Explain the functions of the major hardware components of a computer
system.
Content:
CPU, CU, ALU; main memory, secondary storage, input and output devices
Notes: The major hardware components of a computer system
The major hardware components of a computer system are shown in the diagram below.
CPU
Input devices
CU
Output devices
ALU
Main Memory
Secondary Storage
Central Processing Unit (CPU)
The CPU is also called the processor. It takes raw data, follows a set of instructions (programs)
and converts it into information. The CPU consists of two smaller units known as the control
unit (CU) and the arithmetic and logic unit (ALU).
Control Unit (CU)
2
This is the main part of the CPU. It directs and coordinates all activities within the CPU. It
determines the sequence in which instructions are executed. The CU executes an instruction by
performing the following steps:
1. Fetching the instructions from memory
2. Decoding the instructions
3. Fetching the data required by the instructions from memory
4. Sending the data and instructions to the ALU for processing
5. Sending the data to memory after processing
Arithmetic and Logic Unit (ALU)
The ALU performs all the arithmetic and logic functions in a computer. The arithmetic
operations include addition (+), subtraction (-), multiplication (*) and division (/).
The logic functions are comparisons, such as
1. Equal to (=)
2. Not equal to (≠)
3. Less than (<)
4. Greater than (>)
5. Less than or equal to (<=)
6.
7.
8.
9.
Greater than or equal to (>=)
AND
OR
NOT
Main Memory
Main memory is also called computer memory, immediate access storage (IMAS/IAS) or primary storage. This
unit of memory is directly accessible to the CPU. It holds data and instructions that the computer is processing
at the time.
Secondary Storage
Secondary storage is also called auxiliary storage, backing storage or disk storage. These devices are used to
store data and instructions when they are not being processed. Secondary storage is more permanent than
main memory, since data and instructions are not lost when the power is turned off. It is also much cheaper
than primary storage and is unlimited since you can have as much of it as you can afford. The most commonly
used auxiliary storage devices are magnetic storage (tapes and disks), optical storage (CD ROM, CD-R, DVDROM, DVD-R and DVD-RW and solid state memory (flash memory and USB drives).
Peripheral Devices
Peripheral devices are any device controlled or monitored by the CPU. It includes both input and output
devices.
Input Devices
3
Input devices are any device that is used to put data and instructions into the computer. Some commonly
used input devices are keyboard, mouse, joystick, digital camera, scanners, barcode readers and magnetic
strips.
Output Devices
Output devices are any device that is used to get information out of a computer. Some commonly used output
devices are VDU or monitor, printer, plotter, speakers and multimedia projector.
Objective 1.3: Outline the functions and uses of primary storage devices.
Content:
PROM, EPROM, RAM, ROM
Notes: Primary Storage
This is a group of silicon chips that resides on the computer’s motherboard (main circuit board). Primary
storage consists of two types of memory chips: RAM and ROM chips. A memory chip is an integrated circuit
(IC) made up of millions of transistors and capacitors.
RAM
This chip is used to hold data and instructions (programs) temporarily while processing is taking place using
that data and program. It also holds the data that results from processing – data that is waiting to be output or
stored in a secondary storage device. RAM is volatile i.e. it is temporary and changeable. If the power is turned
off or the computer is rebooted (started up again) all the information held in RAM will be lost.
ROM
This chip holds data and instructions necessary for starting up the computer when it is switched on. It is used
to store system-level programs such as the BIOS (Basic Input Output System) program.
Variations of ROM
Programmable ROM (PROM)
This type of ROM can be programmed only once using special equipment. It is useful for companies that want
to make their own ROMs from software they write themselves. If they change their code they can create new
PROMs without requiring a ROM manufacturer.
Erasable programmable ROM (EPROM)
This type of ROM can be erased and reprogrammed, which makes it more useful than a PROM. EPROM chips
are programmed in the same way as PROM chips. Data is erased from this chip by exposing it to ultraviolet
light of a specific frequency for a specified period of time.
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Objective 1.4: Manipulate units of storage.
Content:
Bistable devices, bit, byte, kilobyte, megabyte, gigabyte, terabyte, word, word size
Notes: Units of Storage
Memory is made up of bistable devices. Bistable means the components that make up memory can be set to
one of two states either on or off. These two states are represented using binary digits- 0 for off and 1 for on.
As such, the smallest unit of storage of memory is called a binary digit (bit). The amount of data and
instructions that can be stored in primary storage or secondary storage media is measured in bytes.
Byte
A byte is made up of a combination of 8 bits and has the capacity to represent one character i.e. a letter, a
number, a symbol, a punctuation mark or a blank space.
Word
A word is the amount of bits the computer can process in one operation.
Word size
A word size or word length is the number of bits in a word.
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Larger Units of Storage
Name
Symbol
Number of bytes
Equal to
Kilobyte
KB
1024
1024 bytes
Megabyte
MB
1048576
1024 KB
Gigabyte
GB
1073741824
1024 MB
Terabyte
TB
1099511627776
1024 GB
Petabyte
PB
1125899906842624
1024 TB
Exabyte
EB
1152921504606846976
1024 PB
Zettabyte
ZB
1180591620717411303424
1024 EB
Yottabyte
YB
1208925819614629174706176 1024 ZB
Objective 1.5: Compare the types of secondary storage media w.r.t. portability, speed and capacity.
Objective 1.6: Use terms associated with storage devices.
Content:
Magnetic tape, floppy disk, hard disk (fixed head, moving head, external), optical disks (CD,
DVD), flash drive, flash memory cards, sequential access, direct access, sectors, tracks,
read/write head; device interfaces such as : SCSI, IDE, SATA
Notes: Secondary Storage Media
Secondary storage devices are chosen for a particular use based on their:
 Storage capacity (how much data the device can store)
 Access speed ( the time needed to locate the data and transmit it to the CPU)
 Portability ( ability to be easily removed and used on another system)
 Cost
 Size (necessary for storage on shelves or portability)
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Magnetic tape
A magnetic tape looks like an audiocassette tape. Tapes may come in different sizes. It is used mainly to
backup hard disks because it can store large amounts of data at a low cost. Accessing data on a tape is very
slow since data is stored sequentially. Sequentially means that data is retrieved in the order which it was
stored. As of 2008, the highest capacity tape cartridges can store 1 TB of data. A tape drive is used to read
data from and write data to the tape. The tape drive may be external or built into the system unit.
Magnetic disks (Floppy disk, Hard disk)
All magnetic disks provide direct access to stored data. This means that you can go directly to specific piece of
data without having to access any other either before or after the data you want.
Floppy disk
This is also called a diskette. It is a removable, flexible plastic disk, coated with a magnetisable material. The
disk is held in a plastic case, usually 3.5 inches by 3.5 inches in dimension. The plastic case protects the disk
from dust and grease. The floppy disk is used to store and transfer small amounts of data between computers.
A 3.5 inch floppy disk holds up to 1.44 MB of data.
Data and information is written to or read from the disk by a read/write head in the disk drive held in the
system unit. Data is stored on both sides of a diskette on tracks and sectors. Tracks are a set of numbered
concentric rings. The tracks are also divided into wedge shaped pieces known as sectors, which are also
numbered. A sector is the amount of data that can be read from or written to a disk by the computer in one
read/write operation.
Sector
Track
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Before data is stored on a floppy disk, it needs to be formatted. Formatting means writing electronic
information on the disk so that the computer can recognize the disk as a valid storage device where data can
be stored. Most floppy disks are already formatted when they are purchased. If a diskette is formatted after
data has been stored to it, the information will be deleted.
Hard disk
A hard disk is a thin but rigid, inflexible disk made of highly polished metal. The surface of each side of the disk
(also called platters) is covered with a substance that can be magnetized. As of April 2009, the highest capacity
HDDs is 2 TB. There are different types of disk: moveable head, fixed head and external. Moveable head hard
disks have one read/write head per disk. Fixed head disks have a read/write head for every track on the disk.
The access time (time to get data) from a spinning disk with one read/write head is a combination of:

Seek time – how long it takes the head to get to the right track;

Rotational delay or latency time – how long it takes for the data to rotate under the head; and

Transmission time – the time taken to read the data and transmit it to the CPU.
Consequently, the access time for a fixed disk is less than that of a moveable disk, since each track has a
read/write head and this eliminates the seek time.
The external and removeable hard disks are portable hard disks that are connected to the system unit.
External hard disks have very large storage capacities, up to 1.5 TB currently. They are used mainly by very
large computers. Hard disks are more reliable than floppy disks since its platters are fixed and seal in a unit.
Hard disks can store much more data than floppy disk and optical disks and access and transmission of data is
faster.
Like floppy disks, a hard disk must also be formatted before any data can be stored on it. Formatting sets up
the tracks, sectors and cylinders. A cylinder is made up of all the tracks of the same number from all the disks
that make up the hard disk.
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Optical Disks
Optical disks are disks that are read by laser lights. They are made from plastic. The data is stored on layers
inside the plastic. CDs and DVDs are the two main types of optical disks.
Compact Disc
A Compact Disc (CD) is an optical disc used to store digital data. The physical dimension of a CD is 12 cm or
occasionally 8 cm in diameter. CDs can hold up to 750 MB. They are three types of CDs: CD-ROM, CD-R and
CD-RW.
CD-ROM (read only)
This type of CD is used for:
 Storing multimedia (text, graphics, sound and videos).
 Storing software packages for sale or distribution e.g. application software packages such as
encyclopedias, word processors, training programs, games and graphics packages.
CD-R (recordable)
This type of CD is used for:
 Storing large volumes of data that does not need to change e.g music CDs.
CD-RW (re-writeable)
This type of CD is used for:
 Storing large volumes of data that change frequently e.g backups copies
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DVD
"Digital Versatile Disc" commonly called “DVD” is an optical disc storage media that can be used for storing
movies with high video and sound quality. DVDs look like compact discs, their physical dimensions are the
same (12 cm or occasionally 8 cm in diameter). DVDs are encoded in a different format to CDs and they have a
much higher density (more data is stored per unit area). Some DVDs are double sided i.e. they can hold data
on both sides. DVDs can hold between 4.7 GB and 17 GB of data. Three types of DVDs are the DVD-ROM (read
only), DVD-R (recordable) and DVD-RW (rewritable).
USB interface
USB Flash drive
USB Flash drives are storage devices which consist of a small circuit board encased in a plastic or metal casing
built with a USB interface. They are typically small, lightweight, removable and rewritable. As of November
2006 to present, memory capacities for USB Flash drives range from 32 MB up to 64 GB. Flash drives are more
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compact, generally faster, hold more data and may be more reliable (due to their lack of moving parts) than
floppy disks.
Common uses
1. Personal data transport
The most common use of flash drives is by individuals to transport and store personal files such as
documents, pictures and video.
2. Computer repair
Flash drives are used to transfer recovery and antivirus software to infected PCs.
3. System administration
Flash drives are used by system and network administrators, who load them with configuration
information and software used for system maintenance, troubleshooting, and recovery.
4. Application carriers
Flash drives are used to carry applications that run on the server computer without requiring
installation.
Flash Memory Cards
These come in the form of a card shaped like a stick of chewing gum, with dimensions 21.5 x 50 x 2.8 mm and
storage capacities up to 64 GB. They are a special type of EEPROM that can be erased and reprogrammed in
blocks instead of one byte at a time. They are used in PDAs (personal digital assistants), laptop computers,
digital audio players, digital cameras, mobile phones and video game consoles.
Storage Device – Capacity, Advantages and Disadvantages
Storage Device
Storage
capacity
Advantages
Disadvantages
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Magnetic tape
Up to 1 TB
 Easy to transport and store
 Cheap
 Mostly used for backup or
archives
Floppy disk
1.44 MB
Fixed hard disks
Up to 2 TB
 Provides direct access to
data stored
 Small and very portable
 Easy to store
 Suitable for backing up
small files
 Data security (e.g. you can
store small files that you
don’t want other computer
users to see)
 Direct access
 Fast data transfer speeds
 Vast storage capacity
 Direct access
 Fast data transfer speeds
 Vast storage capacity
compared to diskettes
 portable
 Direct access
 Fast data transfer speeds
 Vast storage capacity
compared to diskettes
 Portable
 Can be cleaned easily with
a soft cloth
 Unaffected by magnetic
fields
Removable
disks
Optical disks
hard Up to 1.5 TB
CD: up to
8MB
DVD : up to
17 GB
 Provides sequential access to
data stored
 Limited shelf-life (2 years)
 Must be stored in a suitable
environment (smoke, dust,
temperature and humidity
must be carefully controlled)
 Difficult to update files (cannot
make changes to a record
without writing over the entire
tape)
 Small storage capacity
(unsuitable for storing files
containing graphics)
 Limited shelf-life (2 years)
 Slow to read/write speeds
 Not portable
 computer must have a USB port
 Data on CD-ROMs cannot be
changed
 Access times are slower than
hard drives
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Flash memory
Up to 64 GB
USB drive
Up to 256 GB
 Physically very small
 May need special software to
be used with PCs
 Highly portable
 High data transfer speed to  Limited storage compared to
CD or DVD
PCs
 Large storage capacity
compared to diskettes
 Direct access
 Easy to use
 May not be easily read with
computers using Windows 98
 Convenient (small size –
or older operating systems
can be placed in a pocket
or on a key chain)
 Large storage capacity
compared to diskettes
 Highly compatible - ‘plug
and play’ (no software
needed)
 Fast access, direct access
 Password protection
 Disk write protection
switch (prevents data from
being accidentally written
over)
Notes: Device Interfaces
These are connectors and cables used to transfer data from the CPU to input, output and storage devices.
There are different standards or technologies used to design these devices. Three main standards used are:
1. SCSI
2. IDE
3. SATA
Small Computer System Interface (SCSI)
It is a set of standards for physically connecting and transferring data between computers and peripheral
devices. SCSI is most commonly used for hard disks and tape drives, but can connect a wide range of other
devices, including scanners and CD drives.
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SCSI Ribbon cables
Two SCSI Connectors
Intelligent Drive Electronics or Integrated Drive Electronics (IDE)
This interface is used specifically for mass storage devices, in which the controller is integrated into the disk or
CD-ROM drive.
A device controller is a part of a computer system that interprets the signals going to, and coming from the
CPU processor. There are many device controllers in a computer system. Any device connected to the
computer is connected by a plug and socket, and the socket is connected to a device controller. Device
controllers play an important role in order to operate that device. It’s just like a bridge between the device
and operating system.
IDE port connector
IDE motherboard connectors
Serial Advanced Technology Attachment (SATA)
This is a computer bus primarily designed for the transfer of data between a computer and mass storage
devices such as hard disks drives and optical drives.
A computer bus (often simply called Bus) is a part of some computers used to transfer data, signals or power
between some of the components that make up a computer. Computer buses are used to:





Link between the CPU and on-board Memory.
Link between multiple CPUs in a multi-CPU system
Link the Arithmetic logic unit to the rest of the CPU
Connect hard drives, graphics cards, etc to the main system.
Connect SATA, USB and Firewire.
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SATA power cable
SATA ports on a motherboard
Objective 1.7: Explain the uses of various input devices and media
Content:
Optical mark reader(OMR), character readers(OCR, MICR), mouse, joystick, barcode reader,
document scanner, light pen, touch terminals, Voice Data Entry/voice recognition, graphics tablets, point of
sale(POS), keyboard, digital camera, biometric systems, sensors, remote control, sound capture, pointing
devices, webcam
Notes: Input Devices
Optical Mark Reader (OMR)
OMR detects the position of marks on paper. The marks must be made in pre-defined positions. The OMR
detects the intensity of the light reflected from these marks. The computer records the position of the marks
and analyses it determine the meaning of the data e.g. right or wrong answer on a multiple choice quiz. OMRs
are used for correcting multiple choice examinations, analyzing data from surveys, counting election ballots
and validating lottery tickets.
Magnetic Ink Character Recognition (MICR)
MICR is mainly used by the banking industry to read cheques. Cheques have the following information
encoded in them:




The cheque number
The bank branch number
The customer’s account number
The amount of money written on the cheque
The amount is written using special magnetic ink which contains iron oxide. The characters on the cheque are
written in a special font and are recognized electronically as it passes through the device. The MICR can only
recognize a specific font and a limited number of characters.
15
Advantages of the MICR:
 Documents are difficult to forge
 Documents can still be read after being folded, soiled etc.
Disadvantages of the MICR:


MICR readers are expensive
The system can accept only a few characters
Optical Character Recognition (OCR)
This is an optical scanner which utilizes special software to read characters from paper. The shapes of different
characters are detected by shining light on them from a photo-electric device and sensing the patterns of
reflected light. The reader software allows each character pattern to be compared with a set of stored
patterns until the closest match is found. The match is then translated into text in the computer so that it can
be manipulated by the user. It is used in the legal service, postal service, utility and financial companies and by
immigration officers at airports.
Advantages of the OCR

OCR is suitable for converting large volumes of printed data into electronic text on the computer so
that it can be manipulated. It is great for archiving books, documents etc
Disadvantages of the OCR

OCR has difficulty understanding handwritten text if the letters are not properly formed. OCR has
difficulty recognizing unusual fonts.
Mouse
The mouse has a ball underneath, which rolls and determines the direction of the cursor, and buttons which
allow the user to make selections. Some mice (plural of mouse) have a scroll wheel that allows you to scroll
through long documents. In addition to moving the cursor, the mouse is used to select and open documents or
programs, move icons from one place to another on the screen, select options from a menu, position the
cursor when preparing and editing documents, and for drawing lines and sizing graphic objects such as
pictures.
Joystick
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This device is used to control movement of the cursor or other objects on the screen by operating a small
lever. It is used mainly for playing games, but it is also used with scanners at hospitals.
Barcode Readers
Barcodes are read by a scanner in which a laser beam scans the barcode and the light is reflected back into the
scanner. The information received by the scanner is sent for processing. Barcode readers give fast error-free
data entry into the computer. It is a fast method of recording the sales of items. Barcode readers are used in
supermarkets, libraries, research, airports, postal services and warehouses.
Document Scanners
These scan text and pictures into the computer. There are many types of scanners:
1. Flatbed scanner: the picture is placed on a flat surface and the image is captured, similarly to how a
photocopying machine works.
2. Handheld scanner: the picture is read while the user drags the scanner over it. The quality of the image
provided by this scanner is poor, but it is useful for quick data capture.
3. Drum scanner: the document to be scanned is mounted on a glass cylinder. These are used in
publishing industry (magazines, books) to capture images with high detail.
4. Sheet-fed scanner: the sheet that contains the image is fed through rollers and the picture is scanned
as the paper passes through.
Light pen
This is shaped like a pen and is connected to a VDU/monitor. It allows you to point and make selections more
accurately on a screen. The tip of the light pen contains a light-sensitive element which, when placed against
the screen, detects the light from the screen and enables the computer to identify the location of the pen on
the screen. Making selections with a light is far more accurate than using your finger to make selections on a
touch sensitive screen. They also allow you to draw directly on the screen. However they are not as accurate
as a digitizing tablet and drawing can become uncomfortable.
Touch Terminal
A touch terminal, also known as a touch screen is a light-sensitive screen that detect when a person touches it,
as well as the area of the screen that was touched. Various options are displayed on the screen and the user
presses the one they want. Touch screens are used on ATMs, microwave ovens, cash registers, at airports,
fast-food outlets, theatre booking offices, etc.
Advantages of the Touch Terminal

The user can select the option very quickly.
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
The user does not require any training to use it.
Disadvantages of the Touch Terminal

The system is expensive.

It is limited to certain applications.
Voice Data Entry/voice recognition
This type of system requires the use of a microphone. It accepts the spoken word as input data or commands.
The computer is programmed to recognize certain patterns of speech. The microphone is used to code human
speech into a sequence of electronic signals. These signals are compared to a set of stored patterns. If they
match, the command or data being entered is accepted by the computer and processed. Voice commands can
be used to control machines or even enter documents in a word processor. It is very useful for physically
disabled persons.
Advantages of the Voice Data Entry

No typing is required

The system can be used remotely e.g. by telephone
Disadvantages of the Voice Data Entry

Recognition of words is still relatively slow since human speech can vary in tone and emphasis of
various parts of words and phrases.

The system is not suitable for use in noisy places.

You may need to program (train) the system to understand your particular voice patterns.
Digitizing tablet
This device looks like a small chalkboard. The tablet detects and transfers drawings made on it to the screen.
The drawings are made with either a stylus (pen-like pointing device) or a puck (mouse-like device). Graphics
tablets are used by architects, mapmakers, artists and designers to create sketches and drawings on the
computer.
Point of Sale (POS)
This is the combination of a barcode reader and computerized cash register. It is usually found in retail outlets.
The barcode reader scans in information from the sale transaction and this is recorded in a centralized
computer which is connected to the cash register. The information collected can also be used for stock control
and sales analysis.
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Advantages of the POS

Customers get quicker and more accurate service, which improves efficiency.

Supermarkets can get instant or continuous stock checks

Saves on paper
Disadvantages of the POS

Barcodes cannot be read by humans
Keyboard
This device is used to enter text data or characters e.g. letters, symbols, numbers and commands specific to a
program.
Digital cameras
This camera captures an image and stores it in memory within the camera. The camera has a sensor that
converts the light into electrical charges. The processor in the camera converts this information into digital
data and stores it on a flash RAM card. The digital images can then be uploaded from the camera to a
computer where they can be displayed, manipulated or printed. The memory can be erased so that more
images can be captured. Unlike normal RAM memory the RAM card is non-volatile. The resolution of the
camera is measured in pixels. The more pixels a camera has the greater the detail captured.
Advantages of a Digital Camera

Photos can be shown on a small screen on the camera, and resized and erased so that you can choose
to store only the images that you want.
Disadvantages of a digital Camera

It is relatively easy to lose or erase the camera’s memory card e.g. accidentally passing it through an
airport x-ray machine.
Biometric Systems
Biometric refers to the science of identifying an individual through their body characteristics such as face
geometry and hand geometry e.g. fingerprints, iris or retinal scans, vein and voice patterns. All these forms of
identifying an individual can be input into a computer system set up for security purposes allowing access to
buildings and bank accounts etc.
Sensors
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Chemical or physical changes in humans and their environment can be converted to electrical signals using
sensors that pass data to a computer, where it is analysed, stored and manipulated by specialized software.
These sensors are useful in medicine, environmental planning and preservation, weather reporting etc.
Sensors can be used to measure things such as heat, light, sound, pressure, strain, acidity(pH), oxygen
concentration, humidity, pulse, water level, water flow, speed, tilt or even a door or valve opening or closing.
Remote Control
A remote control emits a beam of infra-red light that carries data signals. They are used to input data to
televisions, stereo systems, VCRs, DVD players and by computers as a wireless means of communication.
Sound Capture
Microphones are used for sound capture. All modern computers contain built-in microphones and sound cards
to allow voice or music to be recorded. The sound card digitizes the data into a form that the computer can
understand.
Pointing devices
These devices are used by graphical operating systems such as Windows to show the movement of the pointer
or the cursor, and enable the control and selection of objects on the display screen. This group of devices
includes the mouse, trackball, pointing stick, touchpad, joystick, light pen, digitizing tablet and touch screen.
Webcam
A webcam is a video capture device connected to a computer or computer network, often using a USB port or,
if connected to a network, Ethernet or Wi-Fi. Their most popular use is for video telephony, permitting a
computer to act as a videophone or video conferencing station. This camera is used to record and edit video
images (i.e. moving or still images). The images are stored in a format that can be displayed on a web page.
Web cams are used in video conferencing. It is also useful in security surveillance.
Objective 1.8: State the types and functions of output devices.
Content:
Visual display unit (VDU): resolution, types, sizes; printers: impact and non-impact,
types(character, line, page, laser, inkjet, dot matrix); Characteristics: speed, quality, storage
capacity; plotters; audio output devices(speakers, headphones, earphones); microfilm,
hardcopy, softcopy, human readable, machine readable
Notes: Output devices
20
Output devices are equipment used to get information or any other response out of the computer. If the
output can be read by human beings it is said to be human readable. If the output cannot be understood by
humans it is said to be machine readable. Examples of output devices are display screens, speakers, printers,
video graphics card, audio card (sound card) and plotters.
There are two types of output:
1. Softcopy output
2. Hardcopy output
Softcopy output is temporary output e.g. information displayed on a screen or in voice or audio form through
speakers. This kind of output disappears when the computer is switched off since the screen or the speakers
need the computer to work.
Hardcopy output is permanent output e.g. information printed onto paper or film. It is tangible – you can hold
it in your hands.
Softcopy output devices
Display Screens
Display screens (simply screens) are also called monitors or Visual Display Units (VDU). These are used to
output still or moving pictures. There are two types of display screens:
1. Cathode Ray Tubes (CRT): these screens looks like a standard television set.
2. Flat Panel displays: these screens are used mainly with portable computers like laptops, in some
desktop computers and even in the latest television sets. There are two (2) types of flat panel display
screens:
a. Liquid Crystal Display (LCD)
b. Plasma Display
Screens can come in different sizes e.g. 14 inch or 17 inch. They can be either colour or monochrome.
Monochrome means black and white.
Images and text are formed by many tiny dots of coloured light called pixels. A pixel is short for picture
element. A pixel is the smallest unit on the display screen.
The number of pixels determines the resolution of the screen.
Resolution is the clearness or sharpness of an image on a screen. The more pixels there are on screen, the
greater the resolution. Some common resolutions are:
21





VGA (Video Graphics Array) = 640 x 480 pixels
SVGA (Super Video Graphics Array) = 800 x 600 pixels
XGA/XVGA (Extended Graphics Array/ Extended Video Graphics Array) = 1024 x 768 pixels
SXGA (Super Extended Graphics Array) = 1280 x 1024 pixels
UXGA (Ultra Extended Graphics Array) = 1600 x 1200 pixels
A video graphics card is also called a video display adapter. It determines the resolution, number of colours,
and speed with which images appear on the screen.
Audio Output Devices
Speakers, headphones and earphones are used to output sound. The quality of the sound depends on the type
of system used, the size of the speakers and the computer’s audio card. An audio card is used to process
sound in the computer.
Hardcopy output devices
Printers
One way of classifying printers is as:



Character printers: these print one character at a time similar to a typewriter. They are slow.
Line printers: They print a line at a time. Multiple hammer-like keys forming a line of text hit the page
at one time. They are much faster than character printers and are used to print large volumes. They
print a limited number of characters and do not print graphics.
Page printers: these print a whole page at a time. They are therefore even faster and deal with very
large volumes of printed output.
Another way of classifying printers is as:
1. Impact printers
2. Non-impact printers
Impact printers use a printing mechanism called a print head. They make their output by pressing the print
head against a ribbon, which then hits the paper. The main types of impact printers are dot matrix, daisy
wheel and drum, chain or band printers.
Dot matrix printers (character printers)
Characteristics:


Characters are formed from a matrix of dots.
The speed is usually 30 – 550 characters per second (cps)
22





It is very noisy
It is relatively fast
The print obtained is usually poor.
They are useful for low-quality carbon copy prints or printing on continuous sheets of paper e.g.
invoices (bills).
They are not good for printing shaded graphics or photographs.
Daisy wheel printers (character printers)
Characteristics:




It is very noisy
Printing is slow (less than 90 cps).
The text is generally crisp and clean.
The size and font produced can only be changed by using a different daisy, as the characters on the
wheel are fixed.
N.B. This printer is obsolete
Drum, chain or band printer (line printers)
Characteristics:


They are fast (2500 lines per minute.
They are used to print large volumes of information.
Non-impact printers are faster, quieter and produce better quality print than impact printers. Unlike the
impact printer, the printing mechanism makes no contact with the paper. The main types of non-impact
printers are laser printers, inkjet printers and thermal printers.
Thermal printers (character printers)
There are two types of thermal printers:


Direct Thermal printer: this printer uses heated pins to form the characters. These pins come into
contact with special heat-sensitive paper to form darkened dots when the pins reached a specific
temperature, thus shaping the characters. The pins actually burn the dots into the specially coated
paper. Exposure to sunlight and heat tends to darken the thermal paper. The print quality is poor.
Thermal wax transfer printer: the print head of this printer melts a wax-based ink from a transfer
ribbon onto paper. This printer does not require special paper.
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Thermal printers are used in portable calculators, fax machines and some ATMs (automated teller
machines).
Inkjet printers (line printers)
Inkjet printers produce their output by spraying small droplets of ink at high speed into paper, in a pattern.
These printers can print in both black-and-white and colour. They used at home and small offices. The print
quality is good but not as good as the laser printer. Inkjet printers can also produce both text and graphics.
They are cheaper than laser printers.
Laser printers (page printers)
These use a process similar to that of a photocopying machine. They are used in large companies or
institutions such as schools. They can also be found in modern offices. A laser beam and dry powdered ink
called toner produces a very fine dot matrix pattern. This pattern is transferred to the page and then fused
onto it by heat and pressure. These printers can print in black and white or colour. These printers can produce
more than 40 pages per minute (ppm). The print quality is very good. Laser printers produce both text and
graphics. They are very expensive.
Plotters
Plotters use different printing processes e.g. some work like an inkjet printer and others use the same method
as laser printers. They are used to produce documents with high quality graphics in a variety of colours e.g.
maps, architectural drawings and charts. They can print on large sheets of paper. There are three main types
of plotters:



Pen plotters: these use a mechanical arm or rail that holds a pen which can be moved across the page.
Inkjet plotters: these work in the same way as inkjet printers by spraying ink onto the paper.
Electrostatic plotters: these work in the same way as laser printers.
COM (Computer Output on Microfilm/Microfiche)
COM is a method that is used to store computer documents by reducing them in size to fit on very small
photographic sheets of film. They are used to store large volumes of data. These sheets can be read using a
special magnifying machine. Microfilm is a roll of film and microfiche is a rectangular sheet of film on which
many frames/pages of information can be stored.
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Objective 1.9: Describe how data are stored and manipulated within the computer.
Content:
Binary, octal and hexadecimal number systems; binary addition and subtraction. Integers
(positive and negative); sign and magnitude, BCD, two’s complement; representation of
characters, ASCII.
Notes: Data Representation and Storage
The binary system is used by computers to represent data. This number system uses two digits, 0 and 1. These
two binary digits are known as bits (short for binary digits). Different ways are used to store data based on its
medium and type.
Representing Numbers
The number of bits used to represent a number determines the range/number of values that can be
represented. For example, a single bit can represent one of two values, 0 or 1. Therefore the number of values
a bit can store is two, 0 and 1. Likewise, a group of two bits can be used to represent one of four values, 00,
01, 10 or 11. Therefore the number of values two bits can store is four. To determine how many values any
number of bits can store, the following formula is used 2n, where n represents the number of bits being used.
Therefore, a group of three bits can represent 23 values, i.e. 8 values, which are 000, 001, 010, 011, 100, 101,
110 or 111.
Converting decimal to binary
This involves dividing the decimal (base 10) number by 2 and recording the remainders until the result is zero,
then writing out the remainders from left to right but starting from the bottom up.
2
1510
2
7R1
2
3R1
2
1R1
1510 = 11112
0R1
Representing a number using a bit pattern of a given size
25
A number can be represented using bit patterns of different sizes. For example, the 4-bit representation of 15
is 1111 and the 8-bit representation of 15 is 00001111. Zeroes are added to the left of the binary conversion
of the number to make up the number of bits required. The zeroes do not change the value of the number.
(N.B. The number must be within the range of values that can be represented, using that number of bits.)
Converting a binary number to decimal (base 10)
Find the sum of the values of each digit in the binary number. For example, 101102 to decimal
Place value
Binary digits


24
23
22
21
20
16
8
4
2
1
1
0
1
1
0
The value of each digit is the digit multiplied by its place value i.e. 1x16=16, 0x8=0, 1x4=4, 1x2=2, 0x1=0
The sum of the values is 16 + 0 + 4 + 2 + 0 = 2210
Therefore 101102 is 2210.
Adding binary numbers
To add two binary numbers use the following points:
(a)
02
(b)
02
(c)
12
+
02
+
12
+
02
02
12
(d)
12
(e)
12
+
12
+
12
102
+
12
12
112
26
For example, 10112 + 00112
1 1
1 0 1 12
+ 0 0 1 12
1 1 1 02
Representing Signed Integers
Signed integers are positive or negative whole numbers. In binary there are many ways of representing signed
number. Four common methods are:
1. Sign and magnitude
2. Ones complement
3. Two’s complement
4. Binary Coded Decimal (BCD)
Sign and Magnitude
In this method the leftmost bit is used to represent the sign (positive or negative) and the remaining bits
represent the magnitude. A 0 bit indicates that the number is positive (+) and a 1 bit indicates that the
number is negative (-). N.B. The integer zero is neither negative nor positive, but is represented using all
zeroes.
Example, if asked:
Give the 8-bit representation of -3510 using sign and magnitude.
Solution:
1.
Find the binary of 3510 => 1000112
2.
Add two zeroes to the left to get 8 bits => 00100011 2
3.
Change the leftmost bit to a 1 since you need to represent -3510
One’s Complement
Positive numbers are represented as unsigned binary. The negative numbers are represented by flipping all
the digits in the binary equivalent of the number. This means replacing all the zero bits with one bits and
27
replacing all the one bits with zero bits. N.B. The number should be expressed in the bit pattern size required
before the bits are interchanged.
Example, if asked:
Give the 8-bit representation of 1310 using one’s complement.
Solution:
1.
Find the binary of 1310 => 11012
2.
Add four zeroes to the left to get 8 bits => 000011012
3.
Interchange 1 bits for 0 bits and vice versa => 111100102
Two’s Complement
This is the most common method used to represent signed numbers. Positive numbers are represented as
unsigned binary. To represent a negative number using this method, begin by finding the one’s complement of
the number, then add 12 to the result.
Example, if asked:
Give the 8-bit representation of -710 using two’s complement.
Solution:
1.
Find the binary of 710 => 01112
2.
Add four zeroes to the left to get 8 bits => 000001112
3.
Interchange 1 bits for 0 bits and vice versa => 111110002
4.
Add 12 to the result => 111110002 + 12 = 111110012
Sometimes in using two’s complement, results end up with one bit too many. This is dealt with by discarding
the leftmost bit.
Subtracting in Binary Using Two’s Complement
To subtract numbers in binary, find the negative of representation of the number being subtracted, using
two’s complement. Then add it to the number that it is being subtracted from.
Example, if asked:
Subtract 01102 from 10012
Solution:
1.
Express 10012 - 01102 as 10012 + (-01102)
2.
Find the two’s complement representation of -01102 => 10012 + 12 = 10102
3.
Add 10012 to 10102 => 100112
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Binary Coded Decimal (BCD)
In this method each digit of a number is represented as its four- bit binary code. The sign of a number is
represented using a 4-bit code also. The 4-bit representation of positive(+) is 1010 and negative(-) is 1011. The
sign code is placed to the left of all other bits.
Example, if asked:
What is the BCD representation of -25610?
Solution:
1.
Find the 4-bit representation of each digit => 2 = 0010, 5 = 0101 and 6 = 0110
2.
Put each 4-bit representation together => 0010010101102
3.
Attach the sign code to the left of the result above => 10110010010101102
Representing Numbers Using the Octal and Hexadecimal Number System
The Octal and Hexadecimal Number Systems were developed to deal with concerns programmers had when
representing data in binary. There was often the tendency to make transposition errors and calculation errors
because of the many zeroes and ones. In addition, representing data in binary requires a lot of storage.
Octal (Base 8)
This system uses the digits 0, 1, 2, 3, 4, 5, 6, 7.
Converting From Binary to Octal
This can be done by:
1. Separating the binary number into groups of three (3) bits starting from the right; then
2. Convert each group of bits to find its decimal equivalent.
Example, if asked:
1. Convert 0011011012 to octal.
Solution:
1.
Separate the binary number into groups of 3 bits, from the right => 001 101 101
2.
Convert each group to decimal => 1 5 5
Therefore, 0011011012 = 1558
2. Convert 22410 to octal
29
Solution:
1.
Convert 22410 to binary => 111000002
2.
Separate into groups of 3 bits => 11 100
3.
Convert each group to decimal => 3
4
000
0
Therefore, 22410 = 3408
Converting From Octal To Decimal
The method is the same as converting from binary to decimal. The only difference is the place values are
found using powers of 8.
For example, 2138 to decimal


82
81
80
64
8
1
2
1
3
The value of each digit is the digit multiplied by its place value i.e. 2x64=128, 1x8=8, 3x1=3
The sum of the values is 128 + 8 + 3 = 13910
Therefore 2138 is 13910.
Hexadecimal
This is a base 16 numbering system; it uses 16 symbols (the digits 0-9 and the letters A to F).
30
Hexadecimal Table
Decimal Hexadecimal
Numbers Numbers
0
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
A
11
B
12
C
13
D
14
E
15
F
Converting From Binary to Hexadecimal
This can be done by:
3. Separating the binary number into nibbles (4 bits) starting from the right; then
4. Convert each nibble to its decimal equivalent.
Example 1
Convert 2410 to hexadecimal (use 8 bits).
31
Solution:
1.
Convert 2410 into binary =>000110002
2.
Separate the binary number into nibbles, from the right => 0001
3.
Convert each nibble to its decimal equivalent => 1816
1000
Therefore, 2410 = 1816
Example 2
Convert 22410 hexadecimal (use 8 bits).
Solution:
1.
Convert 22410 into binary =>111000002
2.
Separate the binary number into nibbles, from the right => 1110
3.
Convert each nibble to its decimal equivalent => 1410
4.
Since 1410 is represented as E
0000
010
Then, 22410 = E016
Representing Characters
Data that is represented in computers is made up of characters. Characters include:

Numbers (0 to 9)

Alphabetic (lowercase letters and uppercase letters)

Special characters (punctuation marks : , $ / etc.)

Control characters (backspace, delete, insert etc.)
All the characters that a computer can store and process are called the character set of the computer.
Different types of computers may have slightly different character sets, depending on their operating system.
Each character is represented by a code consisting of eight bits, called the character code. The most common
code used is the American standard Code for Information Interchange (ASCII). This code uses seven bits to
represent each character plus an extra bit called the parity bit which is added to help ensure data integrity.
The standard ASCII code defines 128 character codes (0 to 127) where the first 32 are control codes. A control
code is a non-printable code that is used to tell the computer to carry out a command. Programmers use these
codes to assign commands they may want to personalize in computer.
32
ASCII Table
Objective 1.10: Interpret the hardware specifications of a computer system.
Content:
CPU type and speed; memory: capacity, type, word size, speed. Hard drive: capacity, speed;
firewire, expansion slots, ports.
Notes: Computer Specifications
33
Use the following to guide you when required to interpret computer specifications:
CPU:
 Types:
o Make / Brand:
Intel or AMD
o Models:
Pentium, Athlon, Celeron, Duron etc.
 Speed: Gigahertz (GHz) ranging from 4 GHz up
 word size: How many bits it can input/output and process at a time, 32-bit or 64-bit
Hard Disk Drive (HDD):
 interface connector/controller:
PATA Parallel ATA or SATA Serial ATA
 Capacity:
Gigabytes(GB) ranging from 80GB to 500GB
 Speed:
Revolutions /rotations per minute (rpm) usually 7200 rpm for desktops and 5400 rpm
for laptops
Memory:
 Types of Random Access Memory (RAM):
o
DDR: Double Data Rate
o
DIMMs: Dual In-line Memory Modules
o
DDR3: Double Data Rate type 3
o
DDR2: Double Data Rate type 2
o
SDRAM: Synchronous Dynamic Random Access Memory
 Capacity:
Gigabytes(GB) ranging from 2 GB up
 Speed:
Megahertz (MHz) ranging from 533 MHz and up
Expansion slots:


Slots on motherboard used to attach additional devices. Examples are
PCI slots (Peripheral Component Interconnect) for attaching general hardware
AGP slot (Accelerated Graphics Port or Advanced Graphics Port) for attaching video cards
Ports:
An interface on a computer to which you can connect a device. There are several types. Some
types are specific to certain devices. Some of them are:





Serial
Parallel
USB (Universal Serial Bus)
FireWire
Audio




PCMCIA (Personal Computer Memory
Card International Association).
PCI
PS/2
Ethernet
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Objective 1.11: Distinguish between system programs and application programs.
Content:
systems software: operating systems, translators, utilities; Application software:
general purpose, special purpose, custom written, customized, integrated
software
Notes: Software
Software is the name given to all programs that computers use to perform different tasks.
Types of software
There are two main categories of software:
1) Application software
2) System software
Application software:
Application software can also be referred to as Application packages. These programs are
developed to perform specific tasks or solve a particular problem. Application software includes
entertainment software such as games, home or personal software such as CD-ROM
encyclopedias, productivity software such as word processing, spreadsheet packages and
graphics. Application packages can also be grouped as follows:
1) General purpose software
2) Integrated software
3) Specialized software
4) Customized software
5) Custom written or tailor-made software
General purpose software:
This is software that is not written for any specific business. It can be used to suit specific needs
e.g. a teacher can use a spreadsheet package to prepare students` end of term grades reports
and the same spreadsheet software can be used by a salary clerk to prepare pay sheets and
35
bills. General purpose software is also called “off the shelf” software. They are well tested and
are usually relatively cheap.
Three commonly used general purpose packages are:
1) Word processing packages
2) Spreadsheet packages
3) Database packages
Word processing packages:
These packages are also called word processors. They allow you to prepare documents such as
letters, reports, memos, books or any type of correspondence on a computer. Some popular
word processors available are Microsoft Word, Lotus Word Pro and Word Perfect.
Spreadsheet packages:
These packages allow you to organize information into rows and columns so that it can be
operated on easily. It enables you to store numerical data. Some common spreadsheet
packages in use today are Microsoft Excel, Lotus 123 and Quarto Pro.
Database software:
These programs allow you to organize and store related data together, so that specific pieces of
information can be retrieved easily and quickly. Some common database packages in use today
are Microsoft Access, Oracle and MySQL.
Integrated Software:
An integrated software package offers many single purpose programs together as one. These
packages allow data to be transferred easily between the programs. A basic integrated package
may contain a word processor, spreadsheet, database, communication and graphics
presentation program. Examples of integrated software are Microsoft office, Microsoft works,
Lotus SmartSuite and ClarisWorks.
36
Specialized software:
This is software that is written for a specific task. These programs provide features for the
purpose for which they were designed e.g. AutoCAD which was designed specifically to draw
engineering and architectural designs.
Customized software
This is general purpose software which has been modified to meet the needs of its users
(company or individual) better. This is done by writing short programs called macros and adding
them to the general purpose software.
Custom written software:
This is software that has been created to meet the unique requirements of a particular
individual or company. It may be created by individuals within the company or given to a
software house to be created. A software house is a company that specializes in writing
software.
System software
These are programs that manage and support the resources and operation of the computer
system. They enable the running of application software and the management of the system
resources. System software includes operating systems, utility programs and language
translators.
Operating system (OS):
An operating system is a set of programs that controls the operation of a computer. The
computer cannot work without the operating system software. As soon as the computer is
switched on the operating software on the computer is activated and loaded into main
memory. The process of loading the operating system software into memory is called booting.
Some operating systems used in computers are Windows 7, Windows Vista, Windows XP, Linux,
UNIX and the Macintosh Operating System (e.g. MAC 0SX).
37
Language Translators
A translator is a program that translates one programming language instruction(s) into another
programming language instruction(s) without the loss of original meaning. Examples of
translators are interpreters and compilers.
Utility Programs
These allow a user to perform maintenance-type tasks usually related to managing the
computer, its devices, or its programs. Most operating systems include several utility programs
for managing disk drives, printer and other devices and media. Examples of utility programs
are:
Disk defragmenters can detect computer files whose contents are broken across several
locations on the hard disk, and move the fragments to one location to increase efficiency.
Disk checkers can scan the contents of a hard disk to find files or areas that are corrupted in
some way, or were not correctly saved, and eliminate them for a more efficiently operating
hard drive.
Anti-virus utilities scan for computer viruses.
Objective 1.12: Explain the functions of the Operating Systems.
Objective 1.13: Distinguish among multitasking, multiprocessing and
multiprogramming.
Content:
File management, memory management, security, device management,
input/output management, user interface, process management
Notes: Functions of the Operating Systems
The operating system has several functions:
1. Managing computer resources: it allows software and hardware to communicate with
each other and manages the use of input and output devices.
38
2. Managing files and memory: It keeps track of the locations where programs and data
are stored within the computer’s memory and on secondary storage devices. It is also
responsible for the copying, deleting, renaming and backing-up of files.
3. Maintaining security: It prevents unauthorized users from accessing a computer. A
register of all the users’ names and passwords are kept so that anyone who tries to
access the computer must have their username and password verified before they are
allowed to access the computer. It also keeps a record of who accessed the computer,
the length of time it was used by that user and what they did.
4. Managing tasks (processes): It allows the computer to facilitate multitasking,
multiprogramming and multiprocessing. Multitasking allows the computer to appear to
perform many tasks simultaneously (at the same time) e.g. you can play music and type
your IT project at the same time. Multiprogramming allows the computer to appear to
run more than one program at the same time, although at a specific time the CPU is
dealing with only one instruction for one of the several programs being run.
Multiprocessing allows more than one program to run at the same time by linking two
or more computers or processors which can then work on different programs or
different parts of the same program at the same time.
Objective 1.14: Explain the different types of processing modes.
Content:
Batch processing, real-time, on-line, time-sharing.
Notes: Processing modes
The OS also facilitates different processing mode that are selected based on its suitability for
the job to be performed. There are four modes of processing:
(1) Time –sharing: this mode is used in multi-access systems where a single CPU is
shared by several users using individual terminals. This method of processing makes
39
the user believe they have continuous access to the CPU when in fact each user is
given a time slice (small amount of processing time) in turn. This mode of processing
is used at universities where students and lecturers are allowed access to a central
CPU on a mainframe via different terminals throughout the campus.
(2) Batch processing: in this mode the programs and data are collected together in a
batch queue before processing starts. The program and data collected is called a job.
Usually jobs are stored during working time and executed when the computer is
least in use (during the night). This is done in this manner since it does not require
human interaction during processing, once the batch starts it continues until it is
done or an error occurs. This mode is suited for payroll processing, processing utility
bills and credit card billing.
(3) Real-time processing: in this mode the system is automatically updated when a
change or transaction is made. It is interactive, allowing the user and the system to
be in constant communication with up-to-date information. This mode is suitable for
stock systems, airline booking systems, electronic funds transfer systems and control
systems.
(4) Online processing: a system in this mode has access to a network. Unlike the realtime processing system, an online processing system is not updated automatically,
so information is not always current and must be updated frequently.
(5) Providing a user interface: It allows the user to communicate or interact with the
computer.
Objective 1.15: Distinguish between types of user interface.
Content:
Software interface: Command driven, graphical user interface (GUI) , menu
driven (pull-down, pop-up, icons). Hardware interface: touch screens, non-visual
interface, sensors, Braille keyboards
Notes: User Interfaces
40
There are three (3) types of software user interfaces:
1. Command driven interface: This type of interface is used in a DOS operating system. To
communicate with the computer, the user has to type a command in codes or words
when prompt on the display screen. E.g. C :\> dir tells the OS to list all the files on the
hard drive.
2. Menu driven interface: to communicate the user can either use the mouse or arrow
keys to make a selection from a menu which contains commands e.g. Print, Save As,
Open. There are two (2) types of menus:
Pull-down menu – usually drops down from the menu bar when it is clicked.
Pop-up menu – pops up from nowhere when the right mouse button is clicked.
3. Graphical user interface (GUI): This interface is also called WIMP (windows, icons,
menus and pointing devices). To communicate with the user, it uses buttons, icons,
menus and keystrokes to choose commands, start programs and see lists of files and
other options. Icons are small pictures that represent programs, folders, files, tasks etc.
In a The GUI all objects that are related to each other are shown in a window. More
than one window can be opened on the desktop at the same time. The desktop is
common visual background which appears on the display screen when the computer
has finished booting.
Hardware user interfaces:
Touch screens
To communicate with the computer, the user touches the display of the device by a finger or
stylus. This interface incorporates aspects of GUI and allows the user to make selections and
send commands by touching icons on the screen. The interface is used for both input and
output, since you view information and the options available to you on the screen.
Non-visual interfaces
This type of interface utilizes audio (sound) and gestures (head, hand and device) to send
commands and make selections.
41
Sensors
This type of interface utilizes changes (chemical or physical) in the environment to
communicate with the computer.
Braille keyboards
This device aids the blind in communicating with the computer. The keys have raised dots
which represent different characters.
42