Introduction to Computers

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What Is A Computer?

A computer is an electronic device,

operating under the control of
instructions stored in its own memory
unit, that can accept data (input),
process data arithmetically and
logically, produce output from the
processing, and store the results for
future use.

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 Devices that comprise a computer system
Monitor Speake
(output r System unit
) (output
(processor,
)
memory…)
Printer
(output
)

Storage devices
(CD-RW, Floppy,
Hard disk, zip,…)
Mouse
(input)
Scanne Keyboard
r (input)
(input)

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What Does A Computer
Do?

Computers can perform four general

operations, which comprise the
information processing cycle.

 Input
 Process
 Output
 Storage

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Four Operations of the
Processing Cycle

INPUT PROCESS OUTPUT

STORAGE

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 Data and Information
 All computer processing requires data, which is a
collection of raw facts, figures and symbols, such as
numbers, words, images, video and sound, given to the
computer during the input phase.
 Computers manipulate data to create information.
Information is data that is organized, meaningful, and
useful.
 During the output Phase, the information that has been
created is put into some form, such as a printed report.
 The information can also be put in computer storage for
future use.

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 Why Is A Computer So
Powerful?
 The ability to perform the information
processing cycle with amazing speed.
 Reliability (low failure rate).
 Accuracy.
 Ability to store huge amounts of data
and information.
 Ability to communicate with other
computers.

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 How Does a Computer
Know what to do?
 It must be given a detailed list of
instructions, called a computer
program or software, that tells it
exactly what to do.
 Before processing a specific job, the
computer program corresponding to
that job must be stored in memory.
 Once the program is stored in memory
the computer can start the operation by
executing the program instructions one
after the other.
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What Are the Components
of a Computer?

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Input Devices
 Keyboard.
 Mouse.

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The Keyboard
The most commonly used input device
is the keyboard on which data is
entered by manually keying in or typing
certain keys. A keyboard typically has
101 or 105 keys.

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The Mouse
Is a pointing device which is used to
control the movement of a mouse
pointer on the screen to make selections
from the screen. A mouse has one to
five buttons. The bottom of the mouse is
flat and contains a mechanism that
detects movement of the mouse.

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The Central processing
Unit
The central processing unit (CPU)
contains electronic circuits that cause
processing to occur. The CPU interprets
instructions to the computer, performs
the logical and arithmetic processing
operations, and causes the input and
output operations to occur. It is
considered the “brain” of the computer.

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Memory

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 Memory
Random Access Memory (RAM)
 Main feature 1: volatile
⇒ requires continuous supply of electrical power to
retain information
 Main feature 2: cheap in terms of bytes per dollar

⇒ suitable for large volume data storage

 Functions:

⇒ Receive commands / data from keyboard

⇒ Store information ready to be sent to output
⇒ Store currently running programs/their data
⇒ Store immediate data generated by the currently
running programs

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Amount Of RAM In
Computers
The amount of memory in computers is
typically measured in kilobytes or
megabytes. One kilobyte (K or KB)
equals approximately 1,000 memory
locations and one megabyte (M or MB)
equals approximately one million
locations A memory location, or byte,
usually stores one character.
Therefore, a computer with 8 MB of
memory can store approximately 8
million characters. One megabyte can
hold approximately 500 pages of text
information. 16
 Read Only Memory (ROM)

– Main feature 1: non-volatile

⇒ data retain even when the power is off
– Main feature 2: relatively expensive and can only be
written once
⇒ suitable for storing essential data but in small
volume
– Usually used for system boot up and basic control of I/O
devices
⇒ When a computer first powers up, nothing is in RAM
⇒ Need ROM to store the instructions to set up
various I/O devices, such as disk interface card, video
adapter card, sound card, etc.
– ROM is used to store BIOS (Basic Input/Output Systems)

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Output Devices
Output devices make the information
resulting from the processing available
for use. The two output devices more
commonly used are the printer and the
computer screen.

The printer produces a hard copy of

your output, and the computer screen
produces a soft copy of your output.

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Storage Devices
Auxiliary storage devices are used to
store data when they are not being
used in memory. The most common
types of auxiliary storage used on
personal computers are floppy disks,
hard disks and CD-ROM drives.

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Floppy Disks
A floppy disk is a portable, inexpensive
storage medium that consists of a thin,
circular, flexible plastic disk with a
magnetic coating enclosed in a square-
shaped plastic shell.

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 Structure Of Floppy Disks
 Initially Floppy disks were 8-inches wide, they
then shrank to 5.25 inches, and today the
most widely used folly disks are 3.5 inches
wide and can typically store 1.44 megabytes
of data.
 A floppy disk is a magnetic disk, which means
that it used magnetic patterns to store data.
 Data in floppy disks can be read from and
written to.
 Formatting is the process of preparing a disk
for reading and writing.
 A track is a narrow recording band that forms
a full circle on the surface of the disk. 21
 The disk’s storage locations are divided into
pie-shaped sections called sectors.
 A sectors is capable of holding 512 bytes of
data.
 A typical floppy stores data on both sides and
has 80 tracks on each side with 18 sectors per
track.

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 Hard Disks
 Another form of auxiliary storage is a hard
disk. A hard disk consists of one or more rigid
metal plates coated with a metal oxide
material that allows data to be magnetically
recorded on the surface of the platters.
 The hard disk platters spin at a high rate of
speed, typically 5400 to 7200 revolutions per
minute (RPM).
 Storage capacites of hard disks for personal
computers range from 10 GB to 120 GB (one
billion bytes are called a gigabyte).
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 Compact Discs
 A compact disk (CD), also called an optical
disc, is a flat round, portable storage medium
that is usually 4.75 inch in diameter.
 A CD-ROM (read only memory), is a compact
disc that used the same laser technology as
audio CDs for recording music. In addition it
can contain other types of data such as text,
graphics, and video.
 The capacity of a CD-ROM is 650 MB of data.

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Input Devices

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• Devices for the Hand
• Optical Input Devices
• Audio-Visual (Multimedia) Input Devices

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Devices for the Hand

• Pens

• Touch Screens

• Game Controllers

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Devices for the Hand - Pens

• With a pen-based system, you use an electronic pen

to write on the screen and choose commands.

• Pens are common input devices for handheld

computers, like “personal digital assistants (PDAs).”

• Pens are handy for making notes or selecting

commands, not for inputting a lot of text.

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 The user can point, tap,
draw and write on the
computer’s screen with a
pen.
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Devices for the Hand - Touch Screens

• Touch-screen systems accept input directly through

the monitor.

• Touch screens use sensors to detect the touch of a

finger. They are useful where environmental
conditions prohibit the use of a keyboard or mouse.

• Touch-screen systems are useful for selecting options

from menus.

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Devices for the Hand - Game Controllers

• The two primary types of game controllers are

joysticks and game pads.

• Game pads usually provide controls for each hand.

• Joysticks are popular for flight simulator and

driving games.

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Some controllers even provide tactile feedback, such as
vibrations or pulses, to help players “feel” the action in the game.
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Optical Input Devices

• Bar Code Readers

• Image Scanners and OCR (Optical Character

Recognition)

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Bar Code Readers

• Bar code readers can read bar codes—patterns of

printed bars.

• The reader emits light, which reflects off the bar code
and into a detector in the reader. The detector
translates the code into numbers.

• Flatbed bar code readers are commonly found in

supermarkets. Courier services often use handheld
readers.

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Bar code readers
commonly track
sales in retail
stores
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Image Scanners and OCR

• Image scanners digitize printed images for storage and

manipulation in a computer.

• A scanner shines light onto the image and interprets

the reflection.

• Optical character recognition (OCR) software

translates scanned text into editable electronic
documents.

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 Document
being
scanned

Converts
diode signals
to numbers

To computer

Light source, lens

and diode array
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Audio-Visual (Multimedia) Input Devices

• Microphones and Speech Recognition

• Video Input

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Multimedia Input Devices -
Microphones and Speech Recognition

• Microphones can accept auditory input. A

microphone requires a sound card in the PC.

• A sound card can digitize analog sound signals, and

convert digital sound signals to analog form.

• With speech recognition software, you can use your

microphone to dictate text, navigate programs, and
choose commands.

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Analog Sound Signals
Digital Audio Output
[electrical signals]
(ex. 11100011) to
computer

Analog Signals are Digitized 41

Multimedia Input Devices – Video Input

• PC video cameras digitize full-motion images.

• Digital cameras capture still images.

• These cameras break images into pixels and store

data about each pixel.

• Video images may be compressed to use less memory

and storage space.

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