5.basic computer oraganizations
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AnithaPadmanabanBasic Computer
Organizations
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Introduction
A standard fully featured desktop configuration has basically four
types of featured devices
Input Device
Memory Unit
CPU
Output Unit
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Block Diagram
Input Unit Memory Unit
Cache Memory
Registers
ALU
Control Unit
Output Unit
CPU
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Input Unit
It is an electronic device
Feeds the data to the
computer
Usually connected to
the computer through
cables
Typical Input Devices
Include:1. Keyboard
2. Mouse, Scanner
3. Joystick
4. Digitizing Tablet
5. Touch Sensitive Screen
6. Light Pen
7. Space Mouse
8. Digital Stills Camera
9. Magnetic Ink Character Recognition
(MICR)
10. Optical Mark Reader (OMR)
11. Image Scanner
12. Bar Codes
13. Magnetic Reader
14. Smart Cards
15. Voice Data Entry
16. Sound Capture
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Keyboard
Standard data input and operator control device for a computer
It consists of the standard QWERTY layout with a numeric keypad and additional
function keys for control purposes
In includes the following keys:
Alphanumeric Keys : include number and alphabet keys
Function Keys: Perform specific keys such as searching a file or refer web
Modifier Keys: such as shift keys and control keys modify the casing style of a
character or symbol
Cursor Movement Keys: include up, down, left and right keys used to modify the
direction of cursor on the screen
Spacebar Keys: shifts the cursor to the right by one position
Numeric Keypad: uses separate keypads for numbers and mathematical operators
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Mouse
Popular input device.
You move it across the desk and its movement is shown on the screen by a
marker known as a 'cursor'.
You will need to click the buttons at the top of the mouse to select an
option.
Allow the user to select elements on the screen such as tools, icons, buttons
by pointing and clicking them.
The left click of a mouse allows to select an element
The right click of a mouse displays special option such as open, explore, etc.
The scroll option of a mouse allows to scroll up or down of the document.
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Scanner
Converts documents and images as digitized images
Digitized Images
Can be produced as black, white, gray images or colored images
Colored images
Collection of dots, each dot represent a combination of red,
green, blue
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Joystick
Thejoystick is a rotary lever.
Similar to an aircraft's control stick, it enables you to move
within the screen's environment, and is widely used in the
computer games industry.
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Digitizing Tablet
A Digitizing Tablet is a pointing device that facilitates the
accurate input ofdrawings and designs.
A drawing can be placed directly on the tablet, and the user
traces outlines or inputs coordinate positions with a hand-held
stylus.
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Touch Sensitive Screen
A Touch Sensitive Screen is a pointing device that enables the
user to interact with the computer by touching the screen.
There are three types of Touch Screens:
Pressure-sensitive
Capacitive surface
Light beam.
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Light Pen
A Light Pen is a pointing device shaped like a pen and is
connected to a VDU.
The tip of the light pen contains a light-sensitive element
which, when placed against the screen, detects the light from
the screen enabling the computer to identify the location of
the pen on the screen.
Light pens have the advantage of 'drawing' directly onto the
screen, but this can become uncomfortable, and they are not
as accurate as digitizing tablets.
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Space Mouse
The Space mouse is different from a normal mouse as it has
an X axis, a Y axis and a Z axis.
It can be used for developing and moving around 3-D
environments
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Digital Stills Cameras
Digital Stills Cameras capture an image which is stored in
memory within the camera.
When the memory is full it can be erased and further images
captured.
The digital images can then be downloaded from the camera
to a computer where they can be displayed, manipulated or
printed.
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Optical Mark Reader (OMR)
The Optical Mark Reader (OMR) can read information in the
form of numbers or letters and put it into the computer.
The marks have to be precisely located as in multiple choice
test papers.
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Card Reader
This input device reads a magnetic strip on a card.
Handy for security reasons, it provides quick identification of
the card's owner.
This method is used to run bank cash points or to provide
quick identification of people entering buildings.
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Smart Card
This input device stores data in a microprocessor embedded
in the card.
This allows information, which can be updated, to be stored
on the card.
This method is used in store cards which accumulate points
for the purchaser, and to store phone numbers for cellular
phones.
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Memory Unit
Used to store data, instructions for processing data,
intermediate results of processing and final processed
information
Memory
Secondary
Memory
Primary
Memory
Internal
Processor
Memory
Example:
Hard Disk Drive,
Magnetic Tapes,
USB Pen drive
Example:
RAM, ROM
Example:
Cache,
Memory, CPU
registers
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Primary Memory
Contains set of locations with each location occupying 8 bits.
Each bit in the memory is identified by a unique address.
Data stored in binary form
The commonly used primary memories are:
ROM
RAM
Cache Memory
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n
ROM: Read Only Memory
Stores data and instructions even when the computer is
turned-off
It is the permanent memory of computer
It is a chip that is inserted into the mother board
It is generally used to store the Basic Input/output system
(BIOS) which performs the Power On Self Test (POST)
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RAM: Read Only Memory
Information's are retained only when there is a power supply
When the power is switched off information are lost
It is a volatile memory that temporarily stores data and
applications
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Cache Memory
Store data and the related applications that was last processed
by the CPU.
When the processor performs processing it searches the
cache memory and then the RAM for an instruction.
The cache memory always placed between RAM and ROM
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Difference between RAM and ROM
RAM
It is a Read/write Memory
It is a volatile storage device
Data is erased as soon as power
supply is turned off
It is used as the main memory
of a computer system
ROM
It is a Read Only Memory
It is a permanent storage
device
Data remains stored even
after power supply has been
turned off
It is used to store BIOS
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Secondary Memory
Represents the external storage devices that are connected to
the computer
Provide non-volatile memory source used to store information
that are not used currently
Either located in CPU casing of the computer or connected
externally to the computer
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Types of Secondary Memory
The secondary storage devices are classified as:
Magnetic Storage Devices
Optical Storage Devices
Magnetic Optical Storage Devices
Universal Serial Bus
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Magnetic Storage Devices
Stores information that can be read, erased and rewritten a
number of times
Include floppy disk, hard disk and magnetic tapes
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Magnetic Storage Devices
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Optical Storage Devices
Use laser beams to read the stored data
The include CD-ROM, rewritable Compact Disk ( CD-RW) and
digital video disks with Read Only Memory
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Optical Storage Devices
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Magnetic-Optical Storage devices
Used to store information such as large programs, files and
backup data
Informations can be modified multiple times
Provide higher storage capacity because they use laser beams
and magnets for reading and writing data to the device
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Universal Serial Bus
Commonly known as Pen drive
Removable storage device that is integrated on the USB port
Fast and compact
Larger in capacity
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n
Central Processing Unit
Brain of the computer
Responsible for controlling all other components of the
system
The main operation includes four phases:
Fetching instructions from the memory
Decoding the instructions to decide what operations are to be
performed
Executing the instructions
Storing the results back in the memory
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Components of Computer
Arithmetic and Logic Unit
Control Unit
Registers
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ALU
Part of CPU that performs arithmetic and logical operations on data
Arithmetic operations include
Addition
Subtraction
Multiplication
Division
It takes input in the form of an instruction that contains
Opcode : specifies operation to be performed
Operand : specifies data on which the operations is to be performed
Format code : specifies format of the operands such as fixed point or floating point
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Control Unit
Controls the flow ofdata and information
Maintains the sequence of operations being performed by the CPU
Fetches an instruction from the storage area, decodes the instructions and
transmits the corresponding signal to ALU and storage registers
Guides ALU about the operations to be performed suggests i/o devices to
which data is to be communicated
Uses Program Counter (PC) for retrieving the next instruction for execution
Uses status registers for handling conditions such as overflow of data
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Registers
Contains special purpose, temporary storage units known as registers
Are high speed memory locations used for holding instructions data and
intermediate results that are currently being processed
Program Counter (PC) : keep track ofnext instructions to be executed
Information Register (IR) : hold the instructions that to be decoded by
control unit
Memory Address Register (MAR) : hold the address of next location of
memory to be executed
Memory Buffer Register (MBR) : for storing data received from or sent to
CPU
Memory Data Register (MDR) : for storing operands and data
Accumulator (ACC ): for storing results produced by ALU
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Illustration of CPU and memory
Registers
Main Memory
Cache MemoryCPU
Control Unit
ALU
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Output Unit
It is an electronic device, used to communicate the output
obtained after processing a specific tack, to the user
Commonly used output devices are:
Monitor
Printer
Speaker
Headphones
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Monitor
Commonly used output device that produces visual displays
generated by the computer
Also known as screen, connected as an external device to the
CPU using cables
It is in visual representation of textual and graphical
information
Monitor classified ass
Cathode Ray tube Monitor ( CRT )
Liquid Crystal Display Monitor (LCD)
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Monitor
CRT
Large in size
Occupy more space
Available as monochrome, gray scale and
color models
Visual display better the LCD monitor
Inner side of the screen contains red, blue
and green phosphors. When a beam of
electron strikes on the strikes they
irradiates it to produce the image
To change the color displayed by the
monitor the intensity of the beam striking
the screen is varied
LCD
Thin in size, light weighted
Occupy less space
Available as monochrome, gray scale and
color models
Visual display better the LCD monitor
Thin display device that consists of a
number of color or monochrome pixels
arranged in front of a light source or
reflects
Consume a very small amount of electric
power
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Monitor
A monitor characterized by its monitor size and resolution
Monitor Size:
Length of the screen measured diagonally
Resolution:
Expressed as the number of picture elements or pixels of the
screen
Also called dot pitch
Higher resolution produces a clearer image
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Printer
Transfers the text displayed on the screen onto paper sheets
that can be used by the end-user
An external device connected to the computer using cables
Computer converts the documents that is to be printed to
data that is understandable by the printer
Printer driver software also available for conversion
Performance of the printer measured in terms of dots per
inch(DPI) and pages per minute (PPM)
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Printers
Greater the DPI : better the quality
Higher the PDM : higher efficiency
Types of Printers
Dot Matrix
Commonly used in low quality and high volume applications
Inkjet
Generate high quality photographic prints
Slower that dot-matrix
Laser
Produce high quality prints in quicker time without connected to the
computer
Consists of microprocessors, ROM and RAM
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Speaker
An electromechanical transducer that consists an electrical
signal into sound
Attached to the computer to provide audio output
Audio drives to be installed
Sound card used in the computer decides the quality of audio
Speakers varies in quality and price
May have a subwoofer unit, to enhance bass output
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Headphones
Headphones are a pair of small loudspeakers, or less
commonly a single speaker, held close to a user's ears and
connected to a signal source such as an audio amplifier, radio,
CD player or portable media player.
They are also known as stereophones, headsets or,
colloquially, cans.
The in-ear versions are known as earphones or earbuds.
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Other Output Devices
Plotters
Projectors
LCD Projection Panels
Computer Output Microfilm (COM)