THE BASIC COMPONENTS OF

COMPUTERS
WHAT IS A COMPUTER?

A computer is an electronic device

that can accept data and
instructions, process them and/or
store them for later retrieval, and
generates output (usually based on
the processing).
ADVANTAGES OF USING COMPUTERS
 Computers can perform calculations much more
quickly and accurately than humans.
 Large amounts of data can be stored in a small
amount of space.
 Computers can work continuously and perform
repetitive tasks well. Unlike their human
counterparts, computers do not get bored or tired.
 Computers can simulate things that would take too
long, be too dangerous or simply impossible for
humans to attempt.
DISADVANTAGES
 The introduction of computers can cause redundancy in
the workplace. Employees may lose their jobs if a
computer can do a job more efficiently and ultimately
more cheaply.
 Computers make it easy for people to misuse
information. Computers make it easy to store large
amounts of information about people. In some cases this
information can be freely and easily accessed and used
for purposes for which it was not originally intended.
 DISADVANTAGES (CON’TD)
 Down time is when a computer breaks down or data
becomes corrupted. Businesses often rely so much on
technology that when computers fail that have no
back-up manual systems and are temporarily rendered
helpless as a result.
 The introduction of computer systems in the workplace
is expensive.
 There is health risks associated with excessive or
improper use of computers.
A COMPUTER SYSTEM

A computer system is a combination of computer

hardware and software. The hardware consists of the
physical components of the computer, such as the
monitor or the keyboard. In other words the parts of the
computer you can touch are all hardware. Software is
the term that is used to refer to the programs that run on
the hardware.
THE TYPICAL COMPUTER SYSTEM FUNCTIONS
INPUT, OUTPUT, PROCESSING AND STORAGE

There are four stages when entering data (facts

and figures), input, output, processing and
storage.
INPUT- This is when raw data is input or entered
into the computer.
PROCESSING – At this stage the raw data is
processed using the instructions given in a
program to make the output.
INPUT, OUTPUT, PROCESSING AND STORAGE

OUTPUT – At this stage the information that was

processed is ready for output either as
HARDCOPY OR SOFTCOPY.
-HARDCOPY – printed output from a computer.
-SOFTCOPY – seen on the monitor.

STORAGE – After the data is processed, before it

is output it can be stored for later use.
CATEGORIES OF COMPUTER HARDWARE

There are four main categories of computer hardware:

1) The Central Processing Unit (CPU)

2) Input devices, which allow data to be entered
into the computer
3) Output devices, which are used for outputting
(‘sending out’) data from the computer
4) Storage devices, both primary and backing.
THE CENTRAL PROCESSING UNIT

As the name suggests, the Central Processing Unit (CPU) is

the part of the computer that does the processing. It also
controls the transfer of data between memory and the other
devices that make up the computer system. The CPU
consists of:
 The Control Unit (CU)
 The Arithmetic Logic Unit (ALU)
 Memory
THE CONTROL UNIT (CU)

The Control Unit (CU) is the main part of the CPU,

which controls the operations of the CPU. It is used:
1. To direct the operations of the internal processor
components (components that process the data)
2. To control the flow of programs and data in and out
of the primary memory (main memory)
THE CONTROL UNIT (CU)

3. To read and interpret program instructions

(instructions that allow the computer to perform
various tasks)
4. To control the flow of information to and from all
the components of the computer, e.g. input and
output devices (I/O devices), disk drives and
printers.
THE ARITHMETIC / LOGIC UNIT (ALU)

This is the part of the CPU that does the following:

1. Performs arithmetic operations. These operations
include addition, subtraction, division, multiplication,
etc.
2. Performs logical operations. These operations include
reasoning and performing the comparison necessary to
make decisions.
DIAGRAM OF CPU
STORAGE DEVICES
Memory of a computer is used for storing programs and
data. There are two types of storage devices, they are:
1. PRIMARY STORAGE (MAIN
MEMORY/IMMEDIATE ACCESS STORAGE)

2. SECONDARY STORAGE (BACKING

STORAGE/AUXILIARY STORAGE DEVICES)
PRIMARY STORAGE
There are two types of primary storage:
 RANDOM ACCESS MEMORY (RAM). The contents in this type of memory are
temporary and are lost when the computer is turned off (the data is VOLATILE).
RAM is used to store the instructions and data for currently running programs and
the operating system.

 READ ONLY MEMORY (ROM). This type of memory is permanent and the data
stored in it is not lost when the computer is turned off (the data is NON-VOLATILE).
ROM is used to store data that must not be lost even when the computer is turned off,
such as the commands which start up (boot up) the computer. These instructions are
programmed into the ROM chips by the manufacturers.
SECONDARY STORAGE

Unlike primary storage, secondary storage is not done on chips.

Some examples are:
 Hard disks
 Magnetic tape
 Floppy disks
 Microfilm
 CDs
 DVDs

These devices are used to store programs, as well as data that is

not being processed, for later retrieval.
PERIPHERAL DEVICES

Peripherals device are those

hardware devices that are
externally connected to the
computer system.EG.
KEYBOARD, MOUSE,
EXT HARD DISK
TYPES OF COMPUTERS

Computers can be grouped into

supercomputers, mainframes,
minicomputers, and microcomputers.
These are grouped roughly in order
of size and speed
SUPERCOMPUTER
is the general term given to the fastest
computers in the world. These computers are
very large and may take up several rooms.
Because of their tremendous processing power,
supercomputers are used in fields that require
vast amounts of complex mathematical
calculations, such as simulating and nuclear
research.
MAINFRAME
like supercomputers, mainframes are very fast
large-scale computer systems. Mainframes have
a large number of terminals and peripheral
devices because they are used simultaneously by
hundreds of persons. To meet the demands of
the large number of users, they have a large
memory and large storage capacity.
MINICOMPUTER

a minicomputer is a multipurpose
computer system that is smaller and slower
than a mainframe. Minicomputers support
fewer users than mainframes. The
distinction between the two is based
mainly on size and number of users.
MICROCOMPUTER
is a term used to refer to computers that contain
a microprocessor. You know this type of
computer by it familiar name - the PC.
Microcomputers come in different types and
sizes:
 The desktop
 The Laptop
PRIMARY STORAGE MEDIA
THIS DEAL WITH THE VARIOUS ASPECTS
OF PRIMARY STORAGE MEDIA
RANDOM ACCESS MEMORY (RAM)

The content of RAM can be randomly accessed. This

means that data from any location in RAM can be accessed
when needed instead of having to go through each location
in order until you get to the one you want. What is not
apparent from its name, however, is the fact that not only
can the contents of RAM be read – they can also be written
to.The contents of RAM are lost when the computer is
turned off.
READ ONLY MEMORY (ROM)

The contents of ROM cannot be changed

when the ROM is being used by the
computer. They can only be read; hence the
term read only. The contents of ROM are not
lost when the computer is turned off. As a
result, ROM is used to store the commands
and data that are executed each time the
computer is turned on. Like RAM, the
contents of ROM can be accessed randomly.
Other types of ROM

PROGRAMMABLE READ ONLY MEMORY

(PROM)
This type of ROM can be programmed with a special
machine as opposed to using the expensive masks
needed to produce large volumes of ROM chips.
Once a PROM chip is programmed, however, its
contents cannot be changed.
Other types of ROM

ERASABLE PROGRAMMABLE READ ONLY

MEMORY (EPROM)
This type of ROM is designed so that its contents
can be erased using ultra-violet light. Then the chip
can be reprogrammed. This can be done several
times as opposed to a ROM chip which can only be
programmed once.
STORAGE TERMS
This is deal with all terms associated with
storage (Secondary and Primary)
STORAGE TERMS
 A BIT is a unit of storage that has two possible values, 0 and 1. It is the
smallest unit.
 A BYTE is a group of eight bits or one character
 A WORD is the size of data (or instruction) that the CPU can handle in a
single cycle
 WORD LENGTH/ WORD SIZE – the number of bits in a word.
 ADDRESS – the identification of a particular location in the memory where
data or instruction is stored.
 ADDRESS CONTENT – the data or instruction that is stored in a given
address.
 CHARACTER – any digit, letter or symbol.
BISTABLE DEVICES

A BISTABLE device is a device that can exist in one

of two possible states. It can be compared to an on/off
switch. You would have already come across
something that exists in two states – a BIT. A Bit is a
bi-stable device. Another example of a bi-stable device
is a key on a keyboard – it can be either up or down.
AMOUNTS OF STORAGE
INPUT AND OUTPUT DEVICES
INPUT DEVICES

Input devices accept data signals and translate

them for usage and storage in the computer
system.
 POINTING DEVICES
 SCANNERS
 OTHER DEVICES
 POINTING DEVICES

 The MOUSE is your pointing device. As you move the mouse on

its pad, a pointer on the monitor screen moves in the same

direction as the mouse does.

 A JOYSTICK is a lever that can give you a similar control over

things on the screen, but its behaviour is different from that of a

mouse. The joystick is more than just a pointing device.

 POINTING DEVICES

 A TRACK PAD is a small, flat, square pad below the space bar, upon

which you place your finger. As you move your finger across the track

pad’s surface, the pointer moves across the screen.

 A LIGHT PEN looks like a pen with a wire attaching it to the computer

system. When you point at a position on the screen, the software can

find the exact position being indicated, and so you can select, activate

and manipulate items on the display, just as with a mouse.

 POINTING DEVICES

 A GRAPHICS TABLET or GRAPHICS PAD is a flat rectangular

pad between 6 and 30 inches wide. It works with a stylus which

you move along the surface of the pad, to produce drawings in the

computer. The graphics tablet is used mainly for

COMPUTER-AIDED DESIGN (CAD) and drawings.

SCANNERS

A scanner reads picture-type information into

the computer. There are a number of different

devices referred to as scanners.

SCANNING DEVICES

A HAND-HELD SCANNER reads in the picture while being dragged over it.

A FLATBED SCANNER, the original picture is laid flat upon the scanner’s

surface, and the picture is captured in a similar manner to that of a photocopy

machine.

A SHEET-FED SCANNER feeds the original picture in through rollers. The

scanner reads the picture as the paper goes through. The original must be on a

flexible sheet of paper.

SCANNING DEVICES

A BARCODE READER is a device that reads a pattern of bars

representing the code number of the item on which it is printed. The

barcode reader usually passes a small laser beam over the pattern and

reads in the pattern off reflected light.

A MAGNETIC STRIPE READER scans information in the form of

a magnetic stripe, usually on the surface of a card such as a bank card

or credit card.
SCANNING DEVICES

An OPTICAL MARK READER (OMR) can recognize the position of a mark

or set of marks on paper. Usually used in the correction of multiple choice

papers.

OPTICAL CHARACTER RECOGNITION (OCR) is a device that senses the

presence of text by recognizing the characters. When the document is scanned, a

photo-electric device reads the characters, which are then converted to electrical

signals. The signals represent patterns that give an indication of the characters

involved. It is used in reading postal codes.

SCANNING DEVICES

MAGNETIC-INK CHARACTER RECOGNITION (MICR) identifies

data printed using special ink having good magnetic qualities used in the

processing of bank cheques.

POINT OF SALE TERMINALS (POS) – these are terminals to which

input devices like bar code readers are connected, that process transactions

as soon as the data is read, i.e. at the “point of sale”. Such a terminal is

known as a Point Of Sale Terminal. It is connected to a database that allows

it to retrieve and update information about a product. Cash registers can be a

point of sale terminal.

OTHER DEVICES

The TOUCH SCREEN/TERMINAL – a touch screen/terminal is a

light sensitive screen that can detect when a person touches it, as well as

the area of the screen that was touched. Various options are available on

the screen and the user presses the one he/she wants. The system uses

the location of the area that was pressed to determine the correct option.

It is very easy to use and as a result, users do not require training.

OTHER DEVICES

The MICROPHONE is a device that functions in much the same

way as the microphone you see used on stage. When you talk

your sound waves causes a diaphragm to vibrate. These

vibrations are converted into electrical impulses that are then

transmitted to the computer. One application for which a

microphone is used is in Voice Data Entry (VDE).

 OTHER DEVICES

VOICE DATA ENTRY (VDE) is the process by which a person speaks to the

computer through a microphone as a means of entering data. A voice recognition

program converts the spoken words into text.

KEY-TO-DISK SYSTEM – consists of a keyboard, a screen and a disk, as well as a

processor to verify and validate that data. A data-entry clerk types in the data using the

keyboard. The data may be typed a second time in order to verify it. The data is then

saved on a disk. The data from the disk can then be transferred to the high-speed

computer in an entire batch. This is a form of batch data entry.

OTHER DEVICES

The DIGITAL CAMERA is a device that

utilizes a lens in order to take a photograph by
capturing light on some sort of media. Digital
cameras use digital methods to capture and store
images. The data is then stored on a digital
media such as memory cards, floppy disks, etc.
INPUT DEVICES:
ADVANTAGES AND
DISADVANTAGES
INPUT DEVICES
MANUAL INPUT
DEVICES
KEYBOARD

ADVANTAGES DISADVANTAGES

 Most common  Data entry can be

means of entering time-consuming
 Continued use can cause
text
repetitive strain injury
 Relatively  Errors in transcription

inexpensive are common

 Speed of input depends

on the user’s experience

MOUSE

ADVANTAGES DISADVANTAGES

 Commands can be  Hand-to-eye

given directly to the coordination can be
computer a problem
 Can activate
 Shifting between
commands by
keyboard and mouse
selecting icons
can be confusing
directly
JOYSTICK

ADVANTAGES DISADVANTAGES

 Ideal for games  User has to become

such as car racing skilled at the
sensitive movement
of the joystick
TOUCHSCREEN

ADVANTAGES DISADVANTAGES

 User-friendly  A limited number of

 Easy way to input values can be
options and choices
displayed on one
 Can be used by children
screen at a time
and the physically
 More expensive
challenged who are
unable to use other than a standard
input devices monitor
SCANNER

ADVANTAGES DISADVANTAGES

 Relatively cheap  The quality of the

and easy to install image depends on
 Depending on use, the quality of the
flat bed or hand- hard copy, scanner
held scanners can be and scanner
chosen software
KEY-TO-DISK

ADVANTAGES DISADVANTAGES

 Data can be  Requires many

prepared off-line human and
 Data can be computer resources
validated by the  Expensive

program as it is
being entered
VOICE RECOGNITION SYSTEM

ADVANTAGES DISADVANTAGES

 The user can speak  The voice

at normal rates for recognition system
dictation must be trained to
recognise voice
patterns
 Software cannot

interpret all English

meanings
INPUT DEVICES
DIRECT DATA ENTRY
DEVICES
BARCODE READER

ADVANTAGES DISADVANTAGES

Fast and accurate in product

Details and the order


identification
 Data can be input much faster of data stored on the
than it takes to be keyed in strip cannot be
 Not easily damaged and can changes easily
normally still be read if they care
creased or not stuck onto a flat  The price of the
surface
product in not
 Can be printed using a normal
printer and ink and so are cheap to
included in the
produce barcode
POINT-OF-SALES

ADVANTAGES DISADVANTAGES

 Large amounts of  Same limitations as

data can be input for barcode reader
very quickly and
accurately
OPTICAL CHARACTER RECOGNITION (OCR)

ADVANTAGES DISADVANTAGES

 Can speed up the  Accuracy of the text

typing process can be poor
 Not appropriate for
handwritten
documents
MAGNETIC INK CHARACTER RECOGNITION (MICR)

ADVANTAGES DISADVANTAGES

 Is quick and highly  Has limited

efficient applications
 Both humans and  As the use of
machines can cheques becomes
interpret the data obsolete, its use is
in decline
 Not easy to forge
OPTICAL MARK READER (OMR)

ADVANTAGES DISADVANTAGES

 Data input is very  There is limitations to

fast and accurate the number of
responses
 Incorrect or
inconsistent marking
of the sheet may result
in the data being
rejected
Assignment # 1

Paste pictures of ALL input

devices into your exercises book.
Label ALL pictures or LOSS of
MARKS.
10 Marks
OUTPUT DEVICES
MONITOR
MONITOR – a VISUAL DISPLAY UNIT (VDU) is a
television like device that most people call the computer
screen or monitor. Images are displayed on the monitor
using PIXELS in the form of little tiny dots of light. The
screen RESOLUTION refers to the number of pixels that
are displayed on the screen at the same time. It is given as
a figure such as 640 * 480. There are two types of
monitors: CATHODE RAY TUBES (CRT) and LIQUID
CRYSTAL DISPLAY (LCD). CRT uses similar
technology to the television. LCD screens are much
thinner and use
GRAPHICS PLOTTERS

GRAPHICS PLOTTERS – Like printers graphics plotters are devices

that can produce output on paper. However they operate on a different

principle. Instead of producing images and text using print heads, inked

ribbons or laser, they use something a bit more low-tech – pens. It

draws lines on paper using different coloured pens. Plotters are

frequently used in COMPUTER –AIDED DESIGN AND DRAFTING.

COMPUTER OUTPUT ON MICROFILM

COMPUTER OUTPUT ON MICROFILM (COM) – The data to be

stored is loaded in a microfilm recorder that displays the output on a

screen for it to be photographed by a high speed camera. The recording

process is very quick indeed. The photograph may be stored on

microfilm, microfiche or ultra fiche. A microfilm stores large amounts

of textual or picture information in a format with a vastly reduced size.

SPEAKERS AND PRINTERS

SPEAKERS – used for sound

output
PRINTERS – another popular
output device is the printer.
Printers can be placed into two
categories: IMPACT PRINTERS
and NON-IMPACT PRINTERS
IMPACT PRINTERS
IMPACT PRINTERS are printers that transfer
data onto paper by hitting the paper with some
part of the printer in a similar way to a
typewriter. Impact printers tend to be very
noisy. The characters to be printed are pressed
against an inked ribbon onto the paper. There
are two types of impact printers: LINE
PRINTERS and CHARACTER PRINTERS.
Both types of impact printers print on perforated
paper
LINE PRINTERS
 Line printers are printers that can use multiple
print hammers to print an entire line of text at
one time. This type of printer is a high speed
printer which prints an entire line at a time.
Speed for line printers is measured in lines per
minute (lpm).
 They are normally connected to mainframe,

minicomputers and network systems for

printing in manufacturing distribution and
shipping applications.
CHARACTER PRINTERS

Character printers are printers that

print a character at a time. It is slower
than a line printer. Two main types of
character printers are:
 DAISY-WHEEL

 DOT-MATRIX
DAISY-WHEEL PRINTER

These printers use a wheel containing

characters that rotates until the right
character is facing the paper. A
hammer is then used to force the
character into the ink ribbon onto the
paper. It can print high quality text but
not graphics.
DOT-MATRIX PRINTER

These have a print head capable of

firing tiny pins arranged in a
matrix. As the print head moves
back and forth, these pins strike the
ribbon causing dots to be made on
the paper.
NON – IMPACT PRINTERS

Non – impact printers are printers that

print using methods that do not involve
striking the paper or an ink ribbon. They
are generally faster than most impact
printers and a lot quieter.
 INK-JET PRINTERS

 LASER PRINTERS

 THERMAL PRINTERS
INKJET PRINTERS.

Inkjet printers work by spraying thousands of small

dots of electrically charged ink onto a page to form

images. Inkjet printers produce relatively high print

qualities and can accommodate colour, text and

graphics.
LASER PRINTERS

Laser printers form images by charging thousands of dots on a drum with a

very high intensity laser beam. Toner (dried ink) becomes affixed to these

charged points and when paper is pressed against the drum, an image is

formed. The images are permanently fused to the paper using a heating

unit. Laser printers produce very high quality prints, including text,

graphics and colour but they tend to be the most expensive non-impact

printers.
THERMAL PRINTERS

Are printers that print by using heat. Some thermal printers

use a special heat-sensitive paper. Heat is then applied to

the paper to form text and graphics. This type of printer has

low-maintenance cost since you do not have to buy new ink,

toner or print ribbon. Fax machines use this principle.