Computer Definition
A computer is a machine that is used to
store and process data electronically
Types of computer :
1- Personal Computer
2- Network Computer
3-laptop computers
4-PDA
5-Mainframe
Computer
components
Software
Hardware
• Hardware:
- Pieces of equipment that make up a computer system.
- These are the parts you can touch (although many parts
are contained within the computer’s case).
memory
Brain
3
1+2
1+2
Memory
Brain
3
2+1
1+2
Computer
Output devices
Input devices
Computer
hardware
Storage
devices
memory
Output
devices
Input
devices
Central
Processing Unit
CPU
is the brains of the computer. All the "thinking", calculating and
processing is done by the CPU.
The CPU also control the transfer of information between the
secondry and main memory
The speed at which a CPU can process information is Known as its
Clock Speed
This is measured in megahertz (MHz) or gigahertz (GHz).
1 megahertz = 1 million cycles per second.
1 gigahertz = 1000 megahertz.
The CPU also incorporates :
1. an Arithmetic Logic Unit (which performs the calculations and
logical operations within the computer)
2. and a Control Unit (which fetches, decodes and executes data
from the memory).
An input device is any device that is used to supply
information to a computer (as data or for the
selection of commands/menus/icons etc)
Touch screen
Electronic board
Any devices that allows the result of computer
processing activity to be seen or heard
:Output device
: The screen
CRT
LCD
Plasma
Plotter
Speakers
Data Show
Memory
(RAM)
(ROM)
:
•Random access memory is used in a PC to temporarily store data when
you are using applications.
•RAM is also used to store program instructions and feed information to
the CPU to process.
• RAM is not permanent, when you switch off the PC (or shut down), the
contents of RAM are lost or emptied (This is known as volatile memory.)
•This is a special type of memory which contains all the information the
computer needs to switch itself on, check that all its systems are
working and to tell the PC what things are plugged into it.
• It cannot be changed or overwritten by you, and stays the same even
when the PC is switched off.
•Storage drives are used to store and transfer data files.
•After data is entered into a computer, it must be saved
as a file to preserve its contents after the computer is
switched off.
Hard disk Drive:
•HDD Usually fixed inside the computer and
stores large volumes of data, which can be
accessed and retrieved quickly.
•A software application must also install files
onto the hard disk drive in order to run .
•The access time of a HDD is measured in
milliseconds(msec)
Floppy disk drive:
A floppy disk drive is like a hard disk, but with
removable disks called floppies, floppy disks or diskettes. Floppies
can be used to transfer small files from one PC to another (up to
1.4MB)
CD-ROM/DVD-ROM Drive:
CD-ROM (Compact Disk – Read
Only Memory)
CD-ROM -> CD-R -> CD-RW -> DVD -> DVD-R
Other Types of storage devices??
Storage Capacity uses several terms to define the increasing amounts
of data that can be stored
1
1
0
0
1
0
Bit
Byte
1
1
A
bit
: the amount of storage space needed to hold either
a 1 or a 0 in memory (binary numbering ) .This is the
smallest unit of computer memory
byte
Equal to 8 bits , this is the amount of storage space
needed to hold one character
Kilobyte(KB)
bytes 1024
Megabyte(MB)
1024 KB
Gigabyte(GB)
1024 MB
Terabyte
1024 GB
 The
user can judge the performance of a PC
according to how quickly tasks are performed
.
 Factors determine the overall operating
speed of a PC:



The clock speed of the CPU
The Capacity of the RAM
The Capacity and speed of the HDD
Computer
components
Software
Hardware
- Operating systems, office programs and games are examples of
software.
- Software governs when and how various pieces of hardware can be
put to a variety of uses
Operating Systems software :
•Is the software that runs the computer
•Microsoft Windows is the operating system a lot of people
use.
However, there are other forms of Operating systems
software such as Unix, Linux, OS2, BeOS, OS-X (MacOS) and so
on
Operating system cannot run without the BIOS (Basic Input
Output System)
Common Applications Software
Word Processing: Example Microsoft Word
Spreadsheets:. Example Microsoft Excel
Database: Examples Microsoft Access
Presentation: Example
Microsoft PowerPoint
Web browsing
Applications Software must be compatible with the Operating
Systems
BIOS (Basic Input Output System)
Sara Turn on her computer and then open the word
processor to write her homework :
What are the steps taken by the computer to do this task in
order:
1
2
3
4
Run the BIOS software from the ROM
the BIOS crries out the Power On Self Test(POST)
read the OS files from HDD and copy them to the RAM
Load MS word intothe RAM
:
two or more computers connected
together is called a network
Local Area Network(LAN)
Wide Area Network(WAN)
less than one square kilometre is a LAN While any
network covering more than one square kilometre
is WAN .
 Internet
: a vast computer network . Which
allows users all over the world to
communicate with each other .

Connections to the internet are made by an
Internet service Provider (ISP)
 Intranet:
Many medium to large
organizations now operate their own internal
networks that provide similar functions to
the internet
 Extranet : an intranet or part of an intranet
which can be accessed by certain external
users by the internet.