Chapter 2

COMPUTER SYSTEMS
Computer is an electronic device, operating
under the control of instructions stored its
own memory,
i) that can accept data (input)
ii) process the data according to specified
rules (process)
iii) produce results (output)
iv) and store the results for future use
(storage)

INPUT
Input is any data and instructions entered
into the memory of a computer. There are
four types of input which are: text, graphics,
audio and video.

OUTPUT
Output is data that has been processed into a
useful form called information.

STORAGE
Storage is a location in which data,
instructions, and information are save for
future use.

E.g. CD ROM, diskette, hard disk, pen drive,
memory card.

INPUT DEVICE
Input device is any hardware component that
allows users to enter data and instructions
into a computer.

e.g. keyboard, mouse, scanner, barcode
reader

Also pointing devices: mouse, joystick,
trackball, touch screen, pointing stick and
graphic tablet.

OUTPUT DEVICE
Output device is any hardware component
that present information (processed data) to
one or more people.

E.g. Speaker, monitor, LCD projector, printer
and plotter.

PROCESSOR

• The functions of Processor
–To control and coordinates
operations in a computer system.
–To manage main memory
- example: Intel Pentium IV, AMD
Athlon, G4

THE BLOCK DIAGRAM OF INFORMATION
PROCESSING CYCLE

Input Process Output

Storage

User will input the data to be processed by the
processor.
The storage hold databases, files and programs.
The output devices present the processed data
as useful information products for the user.

Function of CPU (Processor)
• To control and coordinates operations in a
computer system.
• To manage main memory.
• Fetch a program instructions or data item
from memory
• Decode the program instructions into signals
that computer can execute.
• Execute the instructions.
• Store (Return) the result of instructions to the
memory.

INFORMATION PROCESSING CYCLE

PROCESS

• The processing unit controls all activities
within the system. For every instruction, the
control unit repeats a set of four basic
operation called the machine cycle(fetch,
decode, execute and store).

MACHINE CYCLE

Fetching

Storing Decoding

Executing

MACHINE CYCLE
• Fetching: the processes of obtaining a
program instructions or data item from
memory.
• Decoding: the process of translating a
program instruction into signals that the
computer can execute.
• Executing: the process of implementing the
instructions in a program.
• Storing: the process of writing the result to
the storage of memory.

• The central processing unit consists of two
parts: the control unit (CU) and the arithmetic
logic unit (ALU). Each part has specified
function. The control unit tells the rest of the
computer system how to carry out a
program’s instructions. It directs the
movement of electronic signals between
memory, which temporarily holds data,
instruction and processed information, and
the arithmetic-logic unit. It also directs these
controls signals between the CPU and input
and output devices.

• Arithmetic-logic unit performs two types of
operations: arithmetic and logical. Arithmetic
operation are fundamental math operations:
addition, subtraction, multiplication and
division. Logical operations consist of
comparisons. That is, two pieces of data are
compared to see whether one is equal to, less
than or greater than.

• The storage is a location in which
data, instructions and information are saved
for future use. Every computer uses storage to
hold system software and application
software. There are two type of storage, which
are primary storage and secondary storage. A
storage device is the computer hardware that
records or retrieve item to and from storage
media.

• Output is data that has been processed into a
useful form, called information. There are four
types of output, which are texts, graphics,
audio and video.

1.4 DATA REPRESENTATION: BIT, BYTE
AND CHARACTER
BIT
• Bit: A bit (short for binary digit) is the smallest
unit of data the computer can process. The
binary system is a number system that has just
two unique digits, 0 and 1 called bits. A bit is
represented by the numbers 1 and 0. These
number represent the binary system. They
correspond to the states of on and off, true
and false, or yes or no.

BYTE

• Byte: Byte is a unit of information built from
bits. When 8 bits are grouped together, as a
unit, they form a byte. Bits and bytes are the
basis for representing all meaningful
information and programs on computers.

CHARACTER

• One byte is equals to 8 bits. One byte
represents a single character such as number,
letter, or symbol. For example, the capital
letter F is represented by binary code
01000110 that can be understood by the
computer system.

• Computer does not understand letters or
numbers or pictures or symbols. Computer
uses a binary system to count as it only
recognizes two states that are 0 and 1.
Number 9 is represented by binary code
00111001. Eight bits grouped together as a
unit are called a byte. A byte represents a
single character in the computer.

ASCII/EBCDIC

1 byte = 8 bits = 1 character
• There are three character codes or coding
schemes to represent characters which are
ASCII, EBCDIC and Unicode. Each eight byte
contain eight bits. A byte provides enough
different combination of 0s and 1s to
represent 256 characters. ASCII is the most
widely used binary code for microcomputers
(Personal Computer). EBCDIC was developed
by IBM and is used primary for large computer
– mainframe and high end server.

• The combination of 0s and 1s are defined by
patterns. These patterns are called coding
system. The 256-character capability of ASCII
and EBCDIC is too small to handle the
characters that are used by other languages
such as Arabic, Japanese and Chinese. The
Unicode coding scheme is designed to solve
this problem. It uses two bytes (16 bits) to
represent one character. This gives it the
capability of representing 65, 536 different
character. This can cover all the world’s
languages. Unicode is downward-compatible
with ASCII, meaning that Unicode can
recognizes ASCII character.

Unicode
2 bytes = 16 bits = 1 character

INTRODUCTION TO BINARY CODING

What is ASCII?

• ASCII (pronounce as-key) is an acronym for
American Standard Code for Information
Interchange used in most computers to
represent letters, numbers and other
characters.

ASCII Code Symbol ASCII code Symbol ASCII Code Symbol

00110000 0 (48) 01000001 A() 00100001 !( )

1 (49) 01000010 B( ) ? (63)

2 (50) C (67) @ (64)

3 ( 51) D (68 ) $ ( 36)

4 ( 52 ) E (69) % ( 37)

5 ( 53 ) F ( 70) & (38)

6 ( 54 ) 01000111 G( ) * (42)

27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
A
0 1 0 0 0 0 0 1
64 1 65
0 1 0 0 0 1 1 1 71
64 4 2 1
G

1.5 The Function of ASCII Code
1. Coding scheme such as ASCII make it possible
for humans to interact with a digital
computer that processes only bits. When you
press a key on a keyboard, the electronic
signal is converted into a binary form the
computer can process and is stored in
memory. Every character is converted to its
corresponding bytes. Software converts the
byte into a human recognizable number,
letter of the alphabet that is displayed on a
screen or is printed.

2. ASCII was established to achieved
compatibility between various types of data
processing equipment making it possible for
components to communicate with each other
successfully.

1.6 UNITS OF DATA MEASUREMENT

KILOBYTE (KB)
In mathematics, 1 KB = 1000 bytes.
In computer, 1 KB = 1024 bytes or
can be said as:

1 KB = 210 bytes
This is how we get the
calculation for 1024 bytes .

Why is 1024 bytes = 1KB?
20 = 1
21 = 2
22 = 4
23 = 8
24 = 16
25 = 32
26 = 64
27 = 128
28 = 256
29 = 512
210 = 1024

MEGABYTE (MB)
1 MB = 1 048 576 bytes or it can be said
as:
1 MB = 220 bytes

GIGABYTE (GB)
1 GB = 1 073 741 824 bytes or it can be
said as:
1 GB = 230 bytes

TERABYTE (TB)
1 TB = 1 099 511 627 776 bytes or it can
be said as:
1 TB = 240 bytes

1.7 CLOCKSPEED OF MEASUREMENT
Megahertz (MHz) & Gigahertz (GHz)

• When people talk about a computer’s
“speed”, they mean how fast it can process
data. In other words, this means the speed
the computer can turn data into information.
Every microprocessor contains a system
clock.
• The clock speed unit is measured in hertz. A
hertz is one cycle per second.

1 Hz = 1 cycle
1 second
1 000 000 cycle
1 MHz =
1 second

1 000 000 000 cycle
1 GHz =
1 second

• Mega is a prefix that’s stands for million. A
computer that operates at 933 MHz
(megahertz) has 933 million clock cycles in
one second. One way of comparing the
performance of personal computers is by
comparing their microprocessor speeds. A
CPU with a higher clock speed can process
more instructions per second that a CPU
operating at 800 MHz. The speed of the
system clock affects only the CPU. It has no
effects on peripherals such as a printer or disk
drive.

• The combination of speed and number of
paths determines the total processing speed
or channel bandwidth. This is because
different processors often use different
architectures. For this reason, a 1.4 GHz
Pentium 4 performs better that a 1.4 GHz
Pentium 3, but it is not as fast as a 1.4 Ghz
Power PC G4 processor.

2.3 THE COMPUTER PORT
• There are different kinds of port in a system
unit. The ports are:
– Serial port
– Parallel port
– Universal Serial Bus (USB)
– Firewire port
• Special purpose port
– MIDI port
– SCSI port
– IrDA port

Serial port

• A serial port is a socket on a computer used to
connect a modem, data acquisition terminal
or other serial devices via slow-speed serial
interface.
• A serial port is used to connect a device to the
system unit by transmitting data one bit at a
time.

Parallel Port
• A parallel port is a socket on a computer used
to connect a printer or other parallel devices
via the computer's parallel interface.
• Unlike a serial port, a parallel port is an
interface that connects devices by transferring
information more than one bit at a time.
Originally, parallel ports were developed as an
alternative to the slower speed serial ports.
Many printers connect to the system unit
using a parallel port.

• This parallel port can transfer eight bits of
data (one byte) simultaneously through eight
separate lines in a single cable. An example of
a parallel port is the printer port.

USB Port

• . A USB port, short for universal serial bus
port, can connect up to 127 different
peripherals together with a single connector.
• It's used to connect all kinds of external
devices, such as external hard drives, printers,
mouse and scanner. It can transfer data to a
speed of 12 megabits per second.

FIREWIRE PORT
• Previously the FireWire port is called IEEE
1394 port, a personal computer (and digital
audio/video) serial bus interface standard.
• FireWire is similar to a USB port in that it can
connect multiple types of devices that require
faster data transmission speeds. Usually
camcorders and other video equipment use
this port to transmit data on a computer. Data
can move across the port at up to 400
megabits per second.

STORAGE

PRIMARY SECONDARY
STORAGE STORAGE

MAGNETIC OPTICAL FLASH
RAM ROM
MEDIUM MEDIUM MEMORY

RAM – random access memory
ROM – read only memory

PRIMARY STORAGE
• There are two types of primary storage which
are RAM and ROM.

RAM is an acronym for Random-Access Memory
which means the data and program in RAM can
be read and written. ROM is an acronym for
Read-Only Memory which means the data or
program in ROM can just be read but cannot be
written at all.

Function of RAM
1. RAM is the main memory in a computer. The
data in RAM can be read (retrieved) or
written (stored).
2. It stores data and programs that can be
accessed directly by the processor.
3. RAM holds temporary instructions and data
needed to complete tasks. This enables the
computer’s CPU to access instructions and
data stored in the memory very quickly.
4. RAM stores data during and after processing.

FUNCTION OF ROM
1. ROM is another type of memory
permanently stored inside the computer.
ROM is non-volatile. It holds the programs
and data when the computer is powered off.
2. Programs in ROM have been pre-recorded. It
can only be stored by the manufacturer; once
it is done, it cannot be changed.
3. Many complex functions, such as start up
operating instructions, translator for high-
level languages and operating systems are
placed in ROM memory.

FUNCTION OF ROM

4. All the contents in ROM can be accessed and
read but cannot be changed.

DIFFERENCES BETWEEN RAM & ROM

RAM Differences ROM
Stores data Data and Stored by
during and after program manufacturer
processing
Stores Content Stores
information information
temporarily permanently
Vey fast, but uses Processing Time Fast, but uses
a lot of power very little power
Volatile Volatality Non-volatile

SECONDARY STORAGE

• Secondary storage is another alternative
storage to keep your work and documents. It
is very useful to store programs and data for
future use. It is installed externally. It is non-
volatile, which means it does not need power
to maintain the information stored in it. It will
store the information until it is erased.

THREE MAIN TYPES OF SECONDARY STORAGE

SECONDARY EXPLANATION
STORAGE
Magnetic Magnetic medium is a non-volatile storage
medium medium. Magnetic disks use magnetic
particles to store items such as data,
instructions and information in disk’s surface.

It can be any type of storage that utilizes
magnetic patterns to represent information.
The devices use disks that are coated with
magnetically sensitive materials.

STORAGE
Magnetic The examples of magnetic storage are:
medium Magnetic disk such as floppy disk, hard disk,
zip disk. Magnetic tape such as video cassette,
tape.

THREE MAIN TYPES OF SECONDARY STORAGE

STORAGE
Optical Optical medium is a non-volatile storage
Medium media that consists of a flat, round, portable
disc made of metal and plastic that is written
and read by a laser.

These media include various types of
Compact Disc, Digital Versatile Discs and Blu-
Ray Disc.

STORAGE
Optical These following forms are often commonly
medium used:
1. CD, DVD and BD: Read only storage, used
for distribution of digital information such
as music, video and computer programs.
2. CD-R and DVD-R: Write once storage, the
data cannot be erased or written over
once it is saved.
3. CD-RW, DVD-RW and DVD RAM. It allows
data have been saved to be erased and
rewritten.

STORAGE
Flash Flash memory is a solid-state media which
memory means they consists entirely of electronic
components and contains no moving parts.

There are two type of flash memory:

1. Memory Memory card: It is used with digital cellular
card phones, MP3 players, digital video cameras
and other portable digital devices.
Examples of memory cards such as
Compact Flash, xD-picture card, memory
stick, secure digital card, multimedia card,
pc card and smart media.

STORAGE
2. Flash
drive Flash drive: It also called USB drives, thumb
drives or pen drives.

COMPUTER
SOFTWARE

SYSTEM APPLICATION
SOFTWARE SOFTWARE

OPERATING UTILITY WORD
SYSTEM SOFTWARE PROCESSING

SPREADSHEET

PRESENTATION

GRAPHIC
EDITOR

WHAT IS OPERATING SYSTEM (OS)?
• An operating system is a set of programs
containing instructions that coordinate all the
activities among computer hardware
resources.
• Types of OS:
– Stand-Alone Operating System (Windows XP, Vista,
Mac OS, LINUX, DOS)
– Network Operating System (Windows NT,
Windows Server 2000, Linux, UNIX, Solaris)
– Embedded Operating System (Windows CE, Palm
OS, Symbian OS, Embeded Linux)

DIFFERENT PLATFORM OF OS

PC PLATFORM APPLE CROSS
OS PLATFORM OS PLATFORM OS
Microsoft Mac OS LINUX
Windows XP Mac OS X UNIX
Microsoft
Windows Vista

THE FUNCTION OF OS
• The functions of OS:
– Starting a computer
– Provide a user interface
– Managing program
– Managing memory
– Configuring devices

STARTING A COMPUTER

• When we start a computer, it loads the
operating system into the computer's
memory. This process is called booting.
Booting means to load and initialize the
operating system on a computer machine. It
can happen in two ways: warm boot or cold
boot.

• WARM BOOT
A warm boot means restarting a computer
that is already on. It normally happens after
installing a new software or hardware or after
an application crashes or stops working.
COLD BOOT
• A cold boot means starting a computer that is
already off. It happens when we turn on a
computer that has been completely powered
off.

PROVIDE A USER INTERFACE
• We interact with software through its user
interface. That is, user interface controls how
you enter data and instructions and how
information is displayed on the screen. Three
types of user interface are
– Command Line Interface
– Menu Driven Interface
– Graphical User Interface

COMMAND LINE USER INTERFACE

• The command-line user interface requires a
user to type commands or press special keys
on the keyboard to enter data and instructions
that instruct the operating system what to do.
It has to be typed one line at a time. For
example, if we want to rename a filename
from ABC.txt to DEF.txt we use the following
command.
• C:>rename abc.txt.def.txt

MENU DRIVEN INTERFACE

• Menu driven user interface enables the user
to avoid memorizing keywords such as copy,
paste and syntax. On screen, menu-drive
interface provide menus such as means
entering commands. It shows all the options
available at a given point a form of text-based
menu.

GRAPHICAL USER INTERFACE (GUI)
• Graphical user interface makes use of the
computer’s graphics capabilities to make
operating system and programs easier to use,
which is also called ‘user-friendly’.
• Graphical user interface interact with visual
images such as buttons, icons and other
graphical objects to issue commands. On the
desktop, we can initiate many actions by
clicking icons that represent computer
resources such as files, programs and
networks connections.

INDIVIDUAL TASK
state the differences between command line
interface & graphical user interface
COMMAND LINE INTERFACE GRAPHICAL USER INTERFACE
(DOS) (Windows/Linux)

Command Line Menu Driven Graphical User
Interface (CLI) Interface Interface (GUI)
Command Menu Driven Icon Driven
Driven Interface Interface
Interface

MANAGING PROGRAM

• Some operating systems support a single user
and only one running program at a time.
Other’s support thousands of runners multiple
programs.

MANAGING MEMORY

• The computer’s operating system is
responsible for managing memory such as:
(a) Allocating data and instruction to an idea of
memory while being processed
(b) Monitoring the contents of memory

CONFIGURING DEVICES

• A driver, short for device driver, is a small
program that tells the operating system how
to communicate with specific device. Each
device on a computer, such as mouse,
keyboard, monitor, printer, digital camera,
card reader and scanner, has its own
specialized set of commands and thus requires
its own specific driver.

UTILITY PROGRAM

• A utility program which is also called a utility is
a type of system software that allows a user to
perform maintenance-type tasks usually
related to managing a computer, its devices or
its programs.

ANTIVIRUS

• Antivirus is a program that protects a
computer against viruses by identifying and
removing any computer viruses found in a
memory or storage media or in incoming files.

DIAGNOSTIC UTILITY

• Diagnostic utility is a utility program that
compiles technical information about a
computer’s hardware and certain system
software programs and then prepares a report
outlining any identified problems.

FILE MANAGER

• File manager is a utility program that performs
functions related to files and disk
management.

SCREEN SAVER

• Screen saver is a utility program that enables a
display device’s screen to show a moving
image or blank screen if no mouse activity
occurs for a specified time.

APPLICATION SOFTWARE

• Application software is a computer program or
a suite of computer programs that performs a
particular function for the user. Application
software includes all programs that perform
specific tasks such as word processing,
spreadsheet, database, presentation, e-mail
and Web browsing

COMMON TYPES OF APPLICATION
SOFTWARE

Word Processing
• Word Processing an office application that
enables user to create, edit, format and print
textual document.
Spreadsheet
• A program that processes information in the
form of tables. Tables cells can hold values or
mathematical formula.

COMMON TYPES OF APPLICATION
SOFTWARE
Presentation
• An application software that allows a user to create
visual aid for presentation to communicate ideas,
messages and other information to a group.
• Graphics Editing
Program that can edit digital representation or
non-text information such as drawing, charts and
photograph.
• Web browser
Examples: Internet explorer, Google Chrome, Mozilla
Forefox

TYPES OF EXAMPLES
SOFTWARE PROPRIETARY OPEN SOURCE
MICROSOFT WORD KWORD
WORD
COREL WORD OPEN OFFICE WRITE
PROCESSING
PERFECT
MICROSOFT EXCEL KSPREAD
SPREADSHEET
COREL QUATTRO PRO OPEN OFFICE
CALC
MICROSOFT AGNUBIS
PRESENTATION POWER POINT
COREL OPEN OFFICE
PRESENTATION IMPRESS
GRAPHIC ADOBE PHOTOSHOP GIMP
EDITOR
COREL DRAW INKSCAPE

Exercise
ASCII Code Symbol
00100001 !( )
? (63)
@ (64)
$ ( 36)
% ( 37)
& (38)
* (42)

PROPRIETARY AND OPEN SOURCE SOFTWARE

• Proprietary software is also called closed
source software. The closed source software
or proprietary software offers a stable system
with support if the software fails or
malfunctions.
• Examples: Windows XP, Windows 7, Microsoft
Office

Open source software is:
• software provided for use, modification and
redistribution
• software that any programmer can download
from the Internet for free and modify with
suggested improvements.
• the only qualification is that changes can't be
copyrighted,
• Examples: OpenOffice.org, PHP-Nuke,The
GIMP, Mozilla, ClamAV,OpenLDAP, Audacity
and RedHat.

THE ADVANTAGES OF USING
PROPRIETARY SOFTWARE

• The software offers a stable system support if it fails or
malfunction.
• The software is safe and guaranteed to be safe from
dubious threats like programming bugs and viruses thus
providing ease of mind for the user.
• The software is easier to install and used as the
production is planned and extensive research is carried
out to ensure users purchase only the best.
• Furthermore, free updates and latest information on the
software are usually provided to the user.

DISADVANTAGES TO USERS OF USING
PROPRIETARY SOFTWARE ARE:

• Users need to spend a long time downloading and
installing security patches to fix bugs announced by
the manufacturer.
• Any improvements would usually require fees, which
is often expensive.
• Users are not allowed to describe and share the
software as that are licenced.
• Customising the software is nearly impossible
because when users buy proprietary software will
receive binary version of the program, not the code
as the code is the maufacturer’s trade secret.

PROPRIETARY AND OPEN SOURCE
SOFTWARE
• Proprietary Software (Closed Source Software)
means the company that developed the
software owns the software, and no one may
duplicate it or redistribute it without that
company’s permission. Users have to pay to
the software company if they want to use the
proprietary software.
• Examples of proprietary software are
Microsoft Office 2007, Windows 7, Corel
Office X3.

ADVANTAGES OF OPEN SOURCE
SOFTWARE

• The source code are available to users and
they have the rights to modify them.
• This will allow improvements to the software
without having to invest large sum of money
in research and development.
• The modified and improved source codes can
be freely redistributed.

DISADVANTAGES OF OPEN SOURCE
SOFTWARE

• The codes are too complicated for novice
users to understand.
• There is no particular official monitoring the
works of a programmer improving the codes.
This is because anyone is free to use, modify
or even distribute the codes.

• Open Source Software is a software that is
free to use and which provides the original
source code used to create it so that advanced
users can modify it to make work better for
them.
• Examples of open source software are Linux,
GIMP, Blender, Inkscape, Mozilla Firefox 3.0,
OpenOffice.org, KOffice.

THE DIFFERENCES BETWEEN PROPRIETARY AND
OPEN SOURCE SOFTWARE
OPEN SOURCE SOFTWARE PROPRIETARY SOFTWARE
LINUX Ubuntu Windows Vista
OpenOffice.org Microsoft Word 2007
GIMP Adobe Photoshop CS3
Purchased with its source code Purchased without its source
code
User can get open source software User must pay to get the
for free of charge proprietary software
Users can modify the software Users cannot modify the
software
Users can install software freely into User must have a license from
any computer vendor before install into
computer
No one is responsible to the software Full support from vendor if
anything happened to the

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Chapter 2