A computer is an electronic device that can accept data as input, manipulate the data through processing, and produce information as output. It comprises various components working together as a system, including input devices, a central processing unit, memory, output devices, and storage devices. A computer is powerful due to its ability to perform the information processing cycle with great speed, reliability, accuracy, and storage capacity as well as its ability to communicate with other computers.

1. 1
Introduction to Computers

2. 2
What Is A Computer?
A computer is an electronic device,
operating under the control of instructions
(software) stored in its own memory unit,
that can accept data (input), manipulate
data (process), and produce information
(output) from the processing. Generally,
the term is used to describe a collection of
devices that function together as a system.

3. 3
Devices that comprise a
computer system
Printer
(output)
Monitor
(output)
Speaker
(output)
Scanner
(input)
Mouse
(input)
Keyboard
(input)
System unit
(processor, memory…)
Storage devices
(CD-RW, Floppy,
Hard disk, zip,…)

4. 4
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 compute 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
compute can start the operation by executing the
program instructions one after the other.

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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

8. 8
Typical Computer
Input Device
Data is entered into the computer
through input devices.
Examples include a keyboard,
Scanner, pen, and speech
Output Device
Several devices take computer output
and present it in various formats to users.
Examples include information shown
on a monitor screen or printed from a
printing device and Speaker
Storage Device
Data and programs may be
permanently stored on various storage
media.
Examples include a floppy disk, hard
disk, and CD-ROM/RW.

9. 9
What Are The Primary
Components Of A Computer ?
 Input devices.
 Central Processing Unit
(containing the control
unit and the
arithmetic/logic unit).
 Memory.
 Output devices.
 Storage devices.

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 This model of the typical digital computer is
often called the von Neumann computer.
CPU
(Central Processing Unit)
Input
Units
Output
Units
Primary Memory

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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.

13. 13
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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The Central Processing Unit
 Central processing unit (CPU) performs the actual
computation or “number crunching” inside any computer.
 Microprocessor made up of millions of microscopic
transistors embedded in a circuit on a silicon chip.
 Control unit sequentially accesses program instructions,
decodes them and controls the flow of data to and from the
ALU, the registers, the caches, primary storage, secondary
storage and various output devices.

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CPU
 Arithmetic-logic unit (ALU) performs the mathematic
calculations and makes logical comparisons.
 Registers are high-speed storage areas that store very
small amounts of data and instructions for short periods of
time.
Instruction Register (Instruction placed here for
analysis)
Program Counter (Which instruction will be
performed next?)
. Instruction Decoding Unit (Decodes the instruction)

17. 17
How the CPU Works

18. 18
BUSES
CPU
PRIMARY
STORAGE
DATA BUS
ADDRESS BUS
CONTROL BUS
INPUT
DEVICES
OUTPUT
DEVICES
SECONDARY
STORAGE

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Memory
Two basic categories of computer memory:
Primary storage and secondary storage.
Primary stores small amounts of data and information
that will be immediately used by the CPU.
Secondary stores much larger amounts of data and
information (an entire software program, for example)
for extended periods of time.

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Primary Storage
 Primary storage or main memory stores three types of
information for very brief periods of time:
– Data to be processed by the CPU;
– Instructions for the CPU as to how to process the data;
– Operating system programs that manage various aspects of the
computer’s operation.
 Primary storage takes place in chips mounted on the
computer’s main circuit board, called the motherboard.
 Four main types of primary storage: register, random
access memory (RAM), cache memory and read-only
memory (ROM).

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Main Types of Primary
Storage
 Registers: registers are part of the CPU with the
least capacity, storing extremely limited amounts
of instructions and data only immediately before
and after processing.
 Random access memory (RAM): The part of
primary storage that holds a software program and
small amounts of data when they are brought from
secondary storage.
 Cache memory: A type of primary storage where
the computer can temporarily store blocks of data
used more often.

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Primary Storage
 Read-only memory (ROM): Type of primary
storage where certain critical instructions are
safeguarded; the storage is nonvolatile and retains
the instructions when the power to the computer is
turned off.
 Flash memory: A form of rewritable read-only
memory that is compact, portable, and requires
little energy.

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Secondary Storage
Memory capacity that can store very large
amounts of data for extended periods of
time.
– It is nonvolatile.
– It takes much more time to retrieve data
because of the electromechanical nature.
– It is cheaper than primary storage.
– It can take place on a variety of media

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Secondary Storage
 Magnetic tape: A secondary storage medium on a
large open reel or in a smaller cartridge or
cassette.
 Sequential access: Data access in which the
computer system must run through data in
sequence in order to locate a particular piece.
 Magnetic disks: A form of secondary storage on a
magnetized disk divided into tracks and sectors
that provide addresses for various pieces of data;
also called hard disks.

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Secondary Storage
 Hard drives: A form of secondary storage that
stores data on platters divided into concentric
tracks and sectors, which can be read by a
read/write head that pivots across the rotating
disks.
 Direct access: Data access in which any piece of
data be retrieved in a nonsequential manner by
locating it using the data’s address.
 Magnetic diskettes: A form of easily portable
secondary storage on flexible Mylar disks; also
called floppy disks.

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Optical Storage Devices
 Optical storage devices: A form of secondary storage in
which a laser reads the surface of a reflective plastic
platter.
 Compact disk, read-only memory (CD-ROM): A form
of secondary storage that can be only read and not written
on.
 Digital video disk (DVD): An optical storage device used
to store digital video or computer data.
 Fluorescent multilayer disk (FMD-ROM): An optical
storage device with much greater storage capacity than
DVDs.

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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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Software is a set of programs through which user can
perform required task.
Software can be classified in to two types
Application Software
Programming language
Application Package
System Software
Operating System
Device Driver Programming
Computer software

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Operating System Software
Operating system software tells the computer
how to perform the functions of loading,
storing and executing an application and how
to transfer data.
Today, many computers use an operating
system that has a graphical user interface
(GUI) that provides visual clues such as icon
symbols to help the user. Microsoft Windows
98 is a widely used graphical operating
system. DOS (Disk Operating System) is an
older but still widely used operating system
that is text-based.

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Operating Systems
 Operating System is set of program which enables user
software to interface with the computer hardware and it
also manages all the hardware resources
 Some of the functions of the Operating System includes
Process control
File control
Secondary Storage Control
I/O Device Control
User Control

31. 31
Operating System Layers