Computer System Organization
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Computer System Organization
System
A system is a group of
integrated parts that have the common purpose for achieving some objectives.
So the following are the three characteristics for a system:
ü
 Organisation
Arrangements of components.
ü
 Interaction Connection of each component.
ü
 Interdependence
Depending of one component to another
ü
 Integration
More than one components working
together.
ü
 Central objective Main/Common goal with highest priority.
So human body, computer, school, bank
are examples for a system.
Functional Units of
Computer (Block Diagram of Computer)
The components of
computer system are:
1) Input Unit. 2) Central Processing
Unit. 3) Output Unit. 4) Memory Unit.
1. Input Unit
The input device
accepts data and information from the user, and then it converts to computer
acceptable form.
They are:
a. Keyboard
b. Mouse
c. Optical
Character Reader (OCR)
d. Optical
Mark Reader (OMR)
e. Magnetic
Ink Character Reader (MICR)
f. Scanner
g. Digital
Camera
h. Web
Camera
i. Bar
Code Reader
j. Microphone
k. Joystick
l. Track
Ball
m. Light Pen
Keyboard
It is used to inputting text data such
as numbers, characters, symbols etc. Usually it consists of 101 to 105 keys.
There is a special key for cursor control, insertion, deletion, scrolling and
also some function keys. A numeric pad is at the right side to input numeric
values.
Working of keyboard
When a key is pressed the processor
inside the keyboard detects pressed key. Then a number corresponding to the
key is passed to the motherboard then to the microprocessor. It converts the
number to the corresponding character.
Mouse
It is a pointing
device to point and select objects from the screen and also draws pictures.
They are 1.
Serial and parallel mouse 2. Optical mouse
Working of Mouse
Two light resources with photo detectors
in optical mouse emit light. It reflects back to small plastic lenses. When
mouse move a grid line detect the light. The mouse returns it as electric
pulse to the processor.
Optical Character
Reader (OCR)
An OCR is a device that can read
characters printed with a predefined font. Characters scanned with optical scanner.
Scanned image converted to ASCII code and compare with original. It is faster
input method with fewer errors. But only limited characters are used. For
proper reading high quality printing is needed.
Optical Mark Reader
(OMR)
They detect marks made
by a dark pencil or pen on special pre printed form. The OMR scan the
document and transform it in to electric pulses. They Used in,
1. Objective
type exam
2. Surveys.
3. Order
forms
Advantages:
Reliable
Speed
Accurate
Magnetic Ink Character
Reader (MICR)
It can recognize human readable
characters printed on documents with magnetic ink and special font. They
mostly used in bank cheques to print cheque number. So speedily manipulate
the cheques with high accuracy.
Scanner
They are used to scan and digitalize
images, documents etc. Here a light source moves to and fro to read the
document. The detectors convert the document to electric pulse.
Digital Camera
A digital camera allows taking digitized
photographs or videos without using films. Without using any other studio
equipments we can directly transfer the image to the computer. To store
images memory card is used.
Web Camera
Mainly used while we
chat or video conferencing to others through internet. The images are less
quality than digital camera.
Bar Code Reader
It converts a pattern of printed bars (a
sequence of black and white lines of different widths) in to a number. A bar
code reader emits light to the code and it reflects back to the device. They
used to identify products, books, certificates etc.
Microphone
They help us to input sound to the
computer. It translates the vibration in the air in to electric pulse. The
sound can store and reuse for voice recognition applications.
Joystick
It is a pointing device used to select
and move objects on the screen. They are mainly used to play simulation
games. It place in a base, it cal move any direction. It has two control
buttons.
Track Ball
It is also a pointing device like mouse.
It has a ball, can rotate to control the cursor movements. They are
especially used in laptops.
Light Pen
Light pen is a pointing device. To draw
pictures, design objects and also put digital signatures directly on the
screen. Here the photocell inside the light pen responses the picture element
on the screen.
2. Central Processing
Unit (CPU)
It is the brain of the
computer. It controls, operates and co-ordinates all operations inside the
computer. It is also called microprocessor which is a single chip. It has two
parts,
1. Control
Unit (CU)
It
co-ordinates and controls all activities of computers
2. Arithmetic
and Logic Unit (ALU)
It
perform all arithmetic and logical operations.The result of arithmetic
operation is either True or False
3. Output Unit
It communicates the result of processing
to the external world. They translate machine representation in to human
readable form. So it is an electro mechanical device.
They are classified in
to three,
1. Visual
Display Unit (VDU)
2. Printers
3. Plotters
Visual Display Unit
(VDU)
It is a standard and
soft copy output device of the computer.
They are classified
into two,
1. Monochrome Monitors
and Colour Monitors with CRT (Cathode Ray Tube)
2. LCD (Liquid Crystal Display) Monitor
Monochrome Monitors
and Colour Monitors with CRT (Cathode Ray Tube)
CRT is a vacuum tube. The rectangular
part is coated with phosphor. An electron gun (In colour Monitor 3 electron
guns for red, green and blue) emits electrons towards the screen. It creates
and glow tiny dots called pixels on the screen. The number of times a monitor
scans the entire screen in each second is called refresh rate.
Disadvantages of CRT
Monitors
They are heavy
Bulky in size
High power consuming
Not portable
Make eyestrain
LCD (Liquid Crystal
Display)
They are made up of special kind of
liquid crystals, placed between two plates. When electricity passed through
it, crystal liquid become solid and blocks the light.
Advantages of LCD
Monitors
They are weightless
Slim size
Low power consuming
Portable
Not make eyestrain
Printers
They are used print the
data on a paper. Printed output is the most useful and convenient form of
information for users. So it is a hard copy device.
They are classified in
to two:
1. Impact
Printers
2. Non
Impact Printers.
Impact Printers
In impact printers
there is physical contact between with print head and paper. It produces
noise. Slow printing speed. It produces poor quality prints.
They are again
classified into two,
1. Line
printers
2. Character
Printers
1. Line printers
They print entire line
of text at a time. So it is used to print large volume of data.
Examples:
1. Drum printer 2. Chain Printer
1.a) Drum printer
It has a rotating cylindrical drum with
characters are embossed on it. Printing hammer is used to strike to print the
lines from the print buffer. A carbon ribbon is placed between paper and
drum. But here we cannot change the font settings.
1.b)Chain Printer
It has a rotating steel band or chain on
which characters are embossed. Each character has print hammers. A carbon
ribbon is used between hammer and chain.
2. Character Printers
They are slow and print a single
character at a time.
Example:
2.a) Dot Matrix
Printer
Characters are formed by the impact of
pin sets. When print head moves pins are strike on the paper. They versatile
(can print both text and graphics), Print cost is low but low speed, low
quality and noisy. But we can change the font settings.
Non Impact Printers
There is no physical contact between
print head and paper. Printing speed is high. It produces high quality with
colour printing. They do not produce noise.
Example:
1. Inkjet Printers 2. Laser Printers
1. Inkjet Printers
Here ink is used as carbon ribbon.
Printing is done by spraying ink to the paper through a nozzle. There is no
physical contact between print head and paper. Printing speed is high. It
gives high quality with colour printing and it does not produce noise.
2. Laser Printers
Here carbon powder (toner) acts as
carbon ribbon. Printing is done by electrostatic process. There is no
physical contact between print head and paper. Printing speed is high. It
gives high quality with colour printing and it does not produce noise. It has
180-300 CPS speed.
Plotters
They are used to produce large drawings
or images. Used to print building plans, machine designing, blue prints etc.
It has arms with coloured pens. Useful in CAD (Computer Aided Design)
They are two
types: 1) Drum plotter 2)
Flat bed plotter
Memory Unit
They are used to store any type of data
and information and also can retrieve when the user or other devices are
needed.
They are classified in
to two,
1) Primary
Memory (Main Memory) 2) Secondary Memory
(Auxiliary Memory)
Primary Memory (Main
Memory)
They are used to store
the data temporarily on the computer system.
They are classified in
to two
1. Random
Access Memory (RAM)
2. Read
Only Memory (ROM)
Random Access Memory
(RAM)
It is used for storing programs for
execution by the CPU and also data accessed and processed by the CPU.
They are classified
into three,
1. Dynamic RAM
(DRAM)
It
frequently refreshes its contents.
2. Static RAM
(SRAM)
It
does not refreshing its contents frequently.
3. Cache
Memory
It
is a high speed buffer in between RAM and CPU
Read Only Memory (ROM)
The data on ROM only to read the
contents cannot modify or edit it. It is used to store permanent programs
like Boot strap loader to boot up the computer.
They are classified
into three,
1) PROM
(Programmable ROM)
2) EPROM
(Erasable PROM)
3) EEPROM
(Electrically EPROM)
Secondary Memory
(Auxiliary Memory)
They are used to store the data
permanently on the computer system.
They are classified in
to two
1. Sequential
Access
Here the data accessed
in a sequential manner i.e. one after another
Example: Magnetic Type
2. Direct /
Random Access
Here the data accessed
from any location randomly.
It is classified in to
two:
Magnetic Disk and Optical Disk
Magnetic Disk
They are classified in
to two
1. Floppy
Disk 2. Hard
Disk
Floppy Disk
It is made up of plastic coated with
magnetic film. Its capacity is 1.44 MB. To rotate this it has a hub at its
centre. A metallic slide protects the read write opening. There is a read
write protection notch.
A floppy drive is used to read the data
from a floppy disk. Data will lose when it kept inside a magnetic field or
other chemicals, because it coated with magnetic substances.
Hard Disk
It contains a group of metallic disks,
coated with magnetic material in a dust proof case. Each plate has read write
head. It has huge capacity from 10 GB to 250 GB. The average delay required
to access data from the disk is called access time. The recordable surface of
a disk is divided into number or invisible concentric circles called Tracks.
Each track again divided into pie shaped segments called sectors.
Optical Disk
They are classified into two,
Compact Disk (CD)
It is made up of a layer of aluminium in
between two plastic plates. Its capacity is 700 MB. It may be CDROM or WORM
(write ones read many) or CD R/W. To read and write high beam of laser light
is used.
Digital Versatile Disc
(DVD)
It is faster and has more storage
capacity than CD. Its capacity is 4.7 GB.
CPU Registers
They are used to retrieve and store data
at an extreme speed when manipulations are done by the CPU on a temporary
basis.
They are classified
into six,
MAR (Memory Address
Register)
MBR (Memory Buffer
Register)
PC (Program Control
Register)
A (Accumulator
Register)
I (Instruction
Register)
I/O (Input Output
Register)
Performance of disk
memories
It means the read write speed of data to
and from the memory.
They are,
a) Access time: The total
time taken to read and write data to and from a disk is called access time.
b) Seek time: Time taken to
locate the head on the track on which data to be read or write on a disk.
c) Latency time: Time
taken for the rotation of the disk to position the head on the right sector
for read and write.
d) Transfer time: Time taken
to transfer data from RAM to disk and vice versa.
e) Hit ratio: It is the
percentage of records updated on every run.
Software
It
is a set of instructions to perform a desired and useful work done by the
help of computers. They are classified in to two. They are 1) System Software
2) Application Software.
System Software
It
is a collection of programs that directly control the computer’s internal
operations and also that help ordinary users to make use of computer
effectively and efficiently. It is also known as system package.
They
are again classified in to two. They are 1) Operating System, 2) Language
Processors.
Operating System
It
acts as an interface between the user and the hardware. It is a set of
programs that control, co-ordinate the operations of a computer and help to
make efficient use of resources. It has the following functions.
Process management, Memory management,
File management, Security and Command interpretation. Example: MS Windows XP,
Language processors
They
are used to translate the assembly or high level language programs or
instructions in to equivalent machine language instruction. They are
classified in to three. They are 1) Assembler 2) Compiler and 3) Interpreter.
Assembler
It
converts machine language or assembly language codes. Which is uses numbers
and memory locations for representing instructions.
Compiler
It
translates all lines of high level language program at a time in to its
equivalent machine code. The language like C++ and VB are used compiler.
Interpreter
It
translates high level language program in line by line in to its equivalent
machine code. The language like BASIC used interpreter.
Compiler v/s Interpreter
Application
Software
Application
software is a set of one or more programs, designed to solve a specified
problem, or do a specific task for an individual or an organization. They are
classified in to three. They are 1) Pre- written packages (General Purpose),
2) Customised software, 3) Tools and Utilities.
Pre- written packages
(General Purpose packages)
It
needs for too many users. They are.
· Word
processors
(MS Word, Open Office Writer, Soft word,
LEAP, ISM)
· Electronic
Spread sheets
(MS Excel, Open Office Calc, VisiCalc,
Lotus and Quattro pro)
· Graphics
and Multimedia
(Adobe Photoshop, Gimp, Paint shop pro,
Maya, Ulead Photo impact)
· Desk
Top Publishing (DTP)
(Adobe PageMaker, CorelDraw, Quark
Express, MS Publisher)
· Database
management systems
(DBMS) (MS Access, My SQL, Oracle)
Customised Software
They
are developed to solve an individual or organization’s need.
Example: Pay roll, Air line reservation,
sales and inventory control, Hospital management, Library management,
Supermarket management, banking, insurance, accounting etc.
Utilities
They
are used to assist the computer for back upping files, scanning viruses etc.
they are Text editor, Backup Utility, Compression Utility(Zipping), Disk
Defragmenter, Antivirus software etc.
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