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Lesson 1: Understanding the Computer System
As an aspiring computer technician, it is very important to know the different
components of a computer system. These are the hardware, software and peopleware.
Each component plays an important role, without each other computer systems will not
work properly.
1.1 Hardware- the physical, touchable, electronic and mechanical parts of a computer
system.
A. Major hardware components of a computer system
The following list represents a basic set of hardware found in most PCs.
1. System Unit- The main part of a microcomputer, sometimes called the chassis.It
includes the following parts: Motherboard, Microprocessor, Memory Chips, Buses,
Ports, Expansion Slots and Cards.
Figure 1. Tower Type System Unit

2. Motherboard / Mainboard / System Board- The main circuit board of a computer. It
contains all the circuits and components that run the computer.
Figure 2. Modern Motherboard
3. CPU (Central Processing Unit) - The processor is the main “brain” or “heart” of a
computer system. It performs all of the instructions and calculations that are needed
and manages the flow of information through a computer.
Figure 3. Examples of CPU (Intel Core 2 Duo and AMD Athlon)
4. Primary storage- (internal storage, main memory or memory) is the computer's
working storage space that holds data, instructions for processing and processed data
(information) waiting to be sent to secondary storage. Physically, primary storage is a
collection of RAM chips.
Two(2) Types of Memory

a. ROM – (Read Only Memory) ROM is non-volatile, meaning it holds data even
when the power is ON or OFF.
b. RAM – (Random Access Memory) RAM is volatile, meaning it holds data only
when the power is on. When the power is off, RAM's contents are lost.
Figure 4. Examples of RAM
5. Expansion Bus - A bus is a data pathway between several hardware components
inside or outside a computer. It does not only connect the parts of the CPU to each
other, but also links the CPU with other important hardware.

Figure 5. Expansion Bus
6. Adapters- Printed-circuit boards (also called interface cards) that enable the
computer to use a peripheral device for which it does not have the necessary
connections or circuit boards. They are often used to permit upgrading to a new
different hardware.
Figure 6. Adapter (Network Adapter)
7. Power Supply Unit (PSU) - Installed in the back corner of the PC case, next to the
motherboard. It converts 120vac (standard house power) into DC voltages that are used
by other components in the PC.
Figure 7. Power supply
8. Hard Disk Drive (HDD) - Also known as hard drive, is a magnetic storage device
thatis installed inside the computer. The hard drive is used aspermanent storage for
data. In a Windows computer, the harddrive is usually configured as the C: drive and
contains theoperating system and applications.

Figure 8. Power supply
9. Optical Drive- An optical drive is a storage device that uses lasers to read data on
the optical media. There are three types of optical drives: Compact Disc (CD), Digital
Versatile Disc (DVD) and Blu-ray Disc (BD).
Figure 9. CD ROM
10. Digital Versatile Disc (DVD) - Designed to optically access data stored on a DVD.
A laser moves back and forth near the disk surface and accesses data at a very fast
rate.
Figure 10. CD ROM
B. Input Devices- Accepts data and instructions from the user or from another
computer system.
Two (2) Types of Input Devices

1. Keyboard Entry – Data is inputted to the computer through a keyboard.
Keyboard- The first input device developed for the PC. Data is transferred to the
PC over a short cable with a circular 6-pin Mini-din connector that plugs into the
back of the motherboard.
Figure 11. Keyboard
2. Direct Entry – A form of input that does not require data to be keyed by someone
sitting at a keyboard. Direct-entry devices create machine-readable data on paper, or
magnetic media, or feed it directly into the computer’s CPU.
Three Categories of Direct Entry Devices
1. Pointing Devices - An input device used to move the pointer (cursor) on screen.
 Mouse- The most common 'pointing device' used in PCs. Every mouse has two
buttons and most have one or two scroll wheels.
Figure 12. Mouse
 Touch screen- A display screen that is sensitive to the touch of a finger or
stylus.Used in myriad applications, including ATM machines, retail point-of-sale
terminals, car navigation and industrial controls. The touch screen became wildly

popular for smartphones and tablets.
Figure 13. Touch Screen Devices
 Light Pen - A light-sensitive stylus wired to a video terminal used to draw pictures or
select menu options. The user brings the pen to the desired point on screen and
presses the pen button to make contact.
F
Figure14. Light Pen
 Digitizer Tablet - A graphics drawing tablet used for sketching new images or
tracing old ones. Also called a "graphics tablet," the user contacts the surface of the
device with a wired or wireless pen or
puck.Often mistakenly called a mouse, the
puck is officially the
"tablet cursor."
Figure15. Digitizer Tablet
2. Scanning Devices- A device that can read text or illustrations printed on paper and
translates the information into a form the computer can use.

Figure 16. Image scanner
Figure 17. Bar Code Reader
3. Voice- Input Devices - Audio input devices also known as speech or voice
recognition systems that allow a user to send audio signals to a computer for
processing, recording, or carrying out commands. Audio input devices such as
microphones allow users to speak to the computer in order to record a voice message
or navigate software.
Figure 18. Microphones
C. Output Devices - Any piece of computer hardware that displays results after the
computer has processed the input data that has been entered.

1. Computer Display Monitor- It displays information in visual form, using text and
graphics. The portion of the monitor that displays the information is called the
screen or video display terminal.
Types of Monitor
a. CRT Monitors - Cathode Ray Tubes (CRT) were the only type of displays for use
with desktop PCs. They are relatively big (14" to 16" deep) and heavy (over 15 lbs).
Figure 19. Cathode Ray Tube Monitor
b. LCD Monitors- LiquidCrystal Display (LCD) technology has been used in laptops for
some time. It has recently been made commercially available as monitors for
desktop PCs.
Figure 20.LiquidCrystal Display Monitor

c. LED Monitors(Light Emitting Diode) - A display and lighting technology used in
almost every electrical and electronic product on the market, from a tiny on/off light
to digital readouts, flashlights, traffic lights and perimeter lighting.
Figure 21.Light Emitting Diode Monitor
2. LCD Projectors- utilize two sheets of polarizing
material with a liquid crystal solution between them. An
electric current passed through the liquid causes the
crystals to align so that light cannot pass through them.
Each crystal, therefore, is like a shutter, either allowing
light to pass through or blocking the light.
F
igure 22.LCD Projector
3.Smart Board - A type of display screen that has a touch sensitive transparent panel
covering the screen, which is similar to a touch screen.
Figure 23. Smart Board

4. Printer- A device that prints text or illustrations on paper.
Types of printer
 Ink-Jet or Bubble-Jet Printer - bprays ink at a sheet of
paper. Ink-jet printers produce high-quality text and
graphics.
Figure 24. Ink- Jet Printer
 Laser Printer - Uses the same technology as copy
machines. Laser printers produce very high quality text
and graphics.
Figure 25. Laser Printer
 LCD and LED Printer- Similar to a laser printer, but
uses liquid crystals or light-emitting diodes rather than a laser
to produce an image on the drum.
Figure 26. LCD Printer
 Line Printer- Contains a chain of characters or pins that
print an entire line at one time. Line printers are very fast,
but produce low-quality print.
Figure 27. Line Printer
 Thermal Printer- An inexpensive printer that works by pushing heated pins against
heat-sensitive paper. Thermal printers are widely used in calculators and fax
machines.
Figure 28. Thermal Printer

5. Speakers -Used to play sound. They may be built into the system unit or connected
with cables. Speakers allow you to listen to music and hear sound effects from your
computer.
D. Ports- External connecting sockets on the outside of the computer. This is a pathway
into and out of the computer. A port lets users plug in outside peripherals, such as
monitors, scanners and printers.
Table 1.The Ports and theirfunction
Type of Port Function Illustration
Serial Port Intended for serial type
mouse and older camera
Parallel Port Also called as printer port.
This is only for old model
printer. It has 25 pins. It is a
female port.
VGA (Video Graphic
Array) Port
Used to connect monitors.
It has 15 pins and it is a
female port.
USB (Universal Serial
Bus) Port
High speed serial interface
that is used with almost all
devices. It is used to
connect latest model
printers, pen drives, cell
phones etc. it has 4 pins.
PS/2 Port Simple, 6-pin, low-speed
serial connections
commonly dedicated to a
keyboard and mouse.
Power Port Intended for power cord.
Type of Port Function Illustration

S-Video Port S-Video connections are
available on certain source
components and video
display devices, and offer a
higher level of video
performance over
composite video signals.
Audio Port Intended for plugging in the
speaker or headset.
LAN (Local Area
Networking) Port
A physical interface often
used for terminating twisted
pair type cables used to
connect computers onto a
local-area networks (LAN),
especially Ethernet RJ-45
connectors
E. Cables and Wires- A cable is most often two or more wires running side by side and
bonded, twisted or braided together to form a single assembly, but can also refer to a
heavy strong rope.
Table 2. The Cables and Connectors
Illustration Function
These jacks are intended for
the PS/2 port specifically for
PS/2 type of keyboard and
mouse.
This type of jack is intended
for the audio and microphone
port.

S-video jack is obviously for
S-Video port
This monitor jack is intended
for the VGA (Video Graphic
Array) port
This USB (Universal Serial
Bus) plug is intended for USB
port. Modern or new model of
peripherals like printer,
camera, scanners and even
other portable computer
attachments used USB type
of plugs.
This printer cable jack is
intended for the parallel port.
RJ45 ("RJ" in RJ45 stands for
"registered jack," since it is a
standardizednetworking
interface and the "45" simply
refers to the number of the
interface standard) is a type
of connector commonly used
for Ethernet networking.

Power cord is the most
important cord because it
connects the computer to the
main source of electricity to
make it functional.
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