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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n

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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n

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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n

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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n

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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n

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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n


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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n



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n


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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n



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n

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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n

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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n

Components of Computer

Arithmetic and Logic Unit

Control Unit

Registers


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n

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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n

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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n

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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n

Illustration of CPU and memory

Registers

Main Memory

Cache MemoryCPU

Control Unit

ALU


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n

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)

5.Basic Computer Oraganizations

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