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UNIT-I

Explain Basic Organization Of a Digital Computer?

Or
Explain With a Block Diagram of the basic components of a computer system?
Or
Explain various Components of a digital computer?
Or
Explain different parts of a computer system?

Ans:
Definition: A computer is an electronic device that accepts data and instructions from the
user, processes data and gives output at very high speed. It can also store large amount of
data and instructions in its memory permanently.

The internal architectural design of a computer system differs from one system model to
another. However the basic organization remains the same for all computer systems.
The block diagram of any computer system is as shown below:

C.P.U
Arithmetic &
Logic Unit
Data & Output Unit Result
Input Unit
Instruction
s

Control Unit

Memory Unit

The solid lines indicate the flow of data and instructions

The dotted lines indicate the flow of electronic signals of the control unit.
Components or Parts of Computer System
The above diagram shows 5 functional units of a computer system. They are
1. Input unit
2. Output Unit
3. C.P.U.
a. Arithmetic & Logic Unit (ALU)
b. Memory Unit
c. Control Unit
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1. Input Unit
The devices that are used for entering data and instructions into the computer system are
called input units. The input unit links the external environment with the computer system.
Eg: Keyboard, Mouse etc.

2. Output Unit
The job of output unit is just reverse of input unit. It means, the devices that are used to
display or print the information are called output units. So it also links the computer system with
external environment.
Eg: Monitor, Printer etc.

3. Central Processing Unit (CPU)

The centralized system that is used for processing and storing data and instructions is
called Central Processing Unit. It is treated as heart of the computer system. The C.P.U. contains
three major components. They are
i. Arithmetic & Logic Unit (ALU)
ii. Memory Unit
iii. Control Unit

i. Arithmetic & Logic Unit (ALU)

The processing of data is done inside the A.L.U. The A.L.U. can perform both arithmetic
and logical operations.
Arithmetic operations: +, –, x, ÷
Logical operations: AND, OR, NOT
Relational operations: <,>, <=,>=, <> and etc.

ii. Memory Unit

The storage area in the computer system is called memory unit. The data and instructions
can be stored in the memory units either temporarily or permanently. We can use primary
memory to store information temporarily and the secondary memory for permanent storage.
Eg: RAM, Hard disk, CD etc.

iii. Control Unit

The control unit controls the operations of all the devices. It activates the devices by
giving the electronic signals. The control unit acts as central nervous system of a computer
system.

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COMPUTER SOFTWARES
A set of instructions given to the computer to solve user problems and to control
different operations of the computer is known as computer software.
(Or)
The set of computer programs and associated documentation related to the effective
operation of a computer is called as software. The software is developed using programming
languages.
The Computer software is classified into TWO main categories:

Softwares

Application Software System Software

1. Application Software
It is a set of programs written to perform specific application such as processing
examination results, Printing electricity bill, Banking system etc. It is also known as application
package. The users solve their problems by using ready packages more easily and quickly.
Some of application packages are:
1. Word processing software.
2. Spreadsheet software.
3. Database Management System software.
4. Presentation software.
5. Communication software.

2. System Software
System software is a set of programs that control the operations of a computer and
devices attached with the computer. It creates links between user and computer as well as
controls the execution of application programs. System softwares are essential for a computer to
do work. Without this software no link can be created between user and computer.

The examples of system software are:

 Operating Systems.
 Utility programs.
 Device Drivers.
 Language Processors.

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TYPES OF COMPUTERS
According to the size, memory and processing speed. Computers are classified in to the
following types. They are
 Analog Computers
 Digital Computers
 Hybrid Computers

Analog Computers:
The Computer in which continuously changeable physical measure, such as electrical
potential, fluid pressure, or mechanical motion, are used to represent (analogously) the
quantities in the problem to be solved.

Digital Computers:
A digital computer is an electronic computing machine that uses the binary digits (bits) 0
and 1 to represent all forms of information internally in digital form.

Hybrid Computers
a computer that uses both analog and digital techniques. The digital component normally
serves as the controller and provides logical operations, while the analog component normally
serves as a solver of differential equations.

Digital Computers

Micro Computers Mini Computers Super Computers Mainframe Workstations

Computers
I. Micro Computers:
A Micro Computer is the smallest and least expensive general purpose processing
system. Functionality, it is similar to any other large systems. Microcomputers are self-
contained units and usually designed to be used by one person at a time. So, these computers are
also called as “Personal Computers”.
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II. Mini Computers:

A Mini Computer is a small size computers i.e., more costly and more powerful than
microcomputers and also more expensive. A mini computer can handle much more input and
output than Micro Computers (PCs). Mini computers are also called as “Midrange
Computers”. Although, some minis are designed for a single user, most are designed to handle
multiple terminals. The most powerful mini computers can serve the input and output needs
hundreds of users at a time.

IV. Super Computers:

These are the most powerful computers and physically they are some of the largest.
These systems are built to process huge amount of data. The super computer can perform more
than one trillion calculations per second. Scientists and engineers frequently built models of
complex processes. They simulate (copy) the processes on a super computer. These computers
help to analyze and calculate global weather patterns. Super computers can cost lakhs of dollars
and consume enough electricity to power dozens of homes.

III. Main Frame Computers:

A large multi user computer system designed to handle huge amount input, output and
storage. We can connect multiple computers or PCs to a mainframe computer for sharing data.
Mainframe computers are used by rare and large organizations like Indian Airlines, Indian
Railways, Banking Systems etc.,
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V. Work Stations
Workstations are also desktop computers. They are however more powerful by providing
processor speed about 10 times that of desktop PCs. Most workstations have a large colour
video display unit. Normally they have main memory around 120 MB to 1GB. The standard
operating system of work station is UNIX. Most of the workstations have built in hardware to
connect to LAN

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DIFFERENCES BETWEEN MINI AND WORKSTATIONS
MINI WORKSTATIONS
1. Mini computer is a computer 1. Work station is also a computer which
which is used to connect various terminals is used to connect various PCs
2. Single user mini computers are commonly
available 2. Workstations are normally designed as
3. Mini computers sometimes are multi user system
called as mid range computer 3. It is commonly a desktop computer
4. It is commonly used in network 4. Workstation is also used as a personal
environment computer
5. The configuration of mini is 5. The configuration of workstations is
higher than workstations lower than mini

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TYPES OF PERSONAL COMPUTERS OR MICRO COMPUTERS:

The Personal computers are classified into following models. They are
I. Desktop Computers or Personal Computer
II. Note Book Computers or Laptop Computers
III. Hand held Computers
I. Desktop Computers or Personal Computers:
The first style of personal computers is desktop model. The term Desktop means the full
size computer i.e., small enough to be used at the desk but too big to carry around.
The desktop models are horizontally oriented systems, which placed flat on a desk or
table was introduced initially later a variation of desktop system is the tower model. In that
tower model the system unit placed vertically and has more space for devices. Tower models are
popular style of desktop system. They are used to commercial applications, educational
institutions etc.,

II. Note Book computers or Laptop computers:

These computers are used by people who need portable computing power out side of the
office or away from home. These computers approximately the shape of 8.5/11 inches can fit
inside the briefcase easily and looks like a notebook. So, these computers are also called as
“Notebook Computers”. These Computers can operate on current or special batteries. Because
of their size notebook computers often feature a smaller display, less memory and less storage
space compared to a full size PC.
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III. Hand Held Computers:

In 1990s many new types of personal computers (PCs) have been introduced and all they
fall into the category of Hand held computers. These tiny computers are also called as “Palm-
Top” computers. It is almost fit in user hands so, they can also know as Mini notebook
computers. These computers do not provide disk but memory can be added through PC-cards.
We can connect these computers to full size computers to exchange the data. The Hand held PCs
classified into three types. They are
1. Personal Digital Assistant (PDA)
2. Cellular
3. H/PC Pro-devices
1. Personal Digital Assistant Computers:
The PDA’s smallest portable computers, which are no longer than a small appointment
book, but it is not powerful than notebook computers. These computers are used for special
applications such as displaying telephone numbers and addresses.

2. Cellulars:
Some advanced cellular phones combine analog and digital cell phone services with e-
mail capabilities. Such phones enable the user to check and send e-mail over the phone.

3. H/PC Pro-Devices:
The latest development in Hand held model is H/PC. The systems are larger than PDA,
but they are not as long as personal computers. It is also having the future, some where between
these models.

PDA CELLULARS H/PC PRO-DEVICES

…………………………….
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INPUT DEVICES
The input devices are used to communicate to the machine. The instructions or data is
send into the computer thru the input devices. The most common input devices are Keyboard,
Mouse, Track ball, Scanner and etc.
KEY BOARD
Keyboard is one of the most commonly used input devices in a computer. The keyboard
is still the primary input device for entering text and numbers. The keyboard sends different
signals to the CPU for processing.
The Standard keyboard layout for personal computers in many styles, different sizes and
shapes. This keyboard contains below hundred keys. The IBM(International Business Machine)
enhance key board contains 104 keys and above. The enhanced keyboard are arranged in the
following five groups
i. Alpha Numeric Keys
ii. Modifier keys
iii. Numeric Key Pad
iv. Function Keys
v. Cursor movement keys
vi. Special purpose keys

i. Alpha Numeric Keys:

The alphanumeric keys are the part of a keyboard that looks like a typewriter. These are
collection of alphabets (A to Z), numeric (0 to 9) and a special key. In addition to letters and
special symbol, this includes combinational keys (Alt, Ctrl, Shift, Tab, etc.,) to perform special
operations.
ii. Modifier Keys: The modifier keys are so named because they are used to modify the input of
other keys. We press another key while holding down one of the modifier keys Shift, Ctrl and Alt.
iii. Numeric Keypad:
These are usually locate at the right side of the key board and appears like a non-
scientific calculator, with the digits (0 to 9) and arithmetic operations +, -, *, /, %, etc.,
iv. Function Keys:
The fourth part of the function keys. These function keys numbered from F1 to F12 are
usually arranged in first row at the top of the keyboard. Each function key performs different
functions based on the application. They allow us to enter input commands with out typing long
string of characters or navigating menus or dialogue boxes.
v. Cursor Movement Keys:
The fifth part of the keyboard is the set of cursor movement keys. They are four arrow
keys () on the right hand side of the keyboard. These are used to change the position of the
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cursor on the screen. These are also called editing keys. In addition the keyboard also contain
some other key in addition to the above groups they are
a) The editing keys (Back space, Delete, Insert)
b) Home /End keys
c) Page Up / Page Down
d) Enter key or Return key
vi. Special Purpose keys:
In addition to five groups the special purpose keys are available in enhanced keyboard.
They are Print screen, Caps lock, Num lock, Esc, Pause/Break and etc.,
Advantages of the keyboard:
1. We can enter any type of data like alphabets, numbers, and special characters etc.,
2. It is one of the primary input device
3. Easy to enter numeric values using numeric keypad
4. We can execute a task by using function keys without typing any string of
characters as a command
5. We can transfer the cursor from one place to another place by using cursor
movement keys.
6. Issuing shortcuts for a task by using modifier keys.
Disadvantages of the keyboard:
1. It is heavy device to enter input compared to other input devices (Mouse,
Trackball etc.,)
2. We can not draw graphics easily
3. Cursor movement is some what difficult compared to other devices (Mouse,
track ball)
4. It occupies more space than other input devices
5. Typing and issuing is difficult than choosing commands
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MOUSE
In 1980’s PCs was used only one input device called keyboard. Today all new PCs
include a pointing device is called a mouse. The mouse is a graphical input device and is used to
position the cursor on the screen. It allows controlling our computer system without having to
type instruction or commands at the keyboard.
The mouse is an on-screen object usually an arrow ( ) that is used to select text, access menus
and programs, files or data that appears on the screen. A mouse lets the user the position the
cursor any where on the screen quickly and easily without having to use cursor movement keys.
Instead of forcing the user to type or issue commands from the keyboard, the mouse based
operating systems let us use commands, menus and dialogue boxes easily.
Using the Mouse:
We can use the mouse to point a location on the screen. For moving the mouse pointer on the
screen, we have to move the mouse forward, backward, left and right on the desk. By using the
mouse we can perform the following operations
 Clicking
 Double Clicking
 Dragging
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 Right Clicking
Clicking: Clicking means moving the mouse on to the item in the screen. Pressing and releasing
the mouse button once.
Double Clicking: Double Clicking means moving the mouse on to the item in the screen
pressing and releasing the mouse button twice.
Dragging: Dragging an item means to position the mouse pointer over the item. Press the
mouse button and hold it down and drag along with it we can then drop the item in a new
position on the screen. This technique is called. Drag and drop editing
Right Clicking: Clicking the right mouse button is known as right clicking. It is generally used
for viewing properties of an item.
Advantages of the Mouse
1. By using mouse we can issue the commands quickly and easily than key board.
2. It is a versatile tool to draw graphics. It occupies less space than keyboard.
3. We can transfer the cursor from one place to another quickly and easily compared to
keyboard.
4. It is also a primary input device used today with PCs.
Disadvantages of the mouse
1. Mouse operations can also apply using key board
2. GUI operating systems are only support the mouse operations
3. There is no facility to enter alphabets, numbers, special characters
4. To operate the mouse we must have the flat surface
TRACK BALL
1. A track ball is a pointing device that uses a ball to position the cursor and works like an
“upside down mouse”. We rest our thumb on the exposed ball and our fingers on the
buttons. To move the pointer around the screen, we roll the ball with our thumb, because we
do not move the whole device. A Track ball requires less space than mouse. When space is
limited a trackball can be an advantage. Track ball gained popularity with the invention of
laptop computers. Like a mouse, track ball come in different models. Some track balls are
large and heavy others are much smaller. In portable computers track ball may be built
directly into the keyboard. It has two or three keys. They are available in right side and left
side models. Trackballs gained popularity at the invention of lap tops.

Advantages of Trackball
1. It occupies less space than mouse
2. It is also used as a versatile tool for graphic designs
3. We can issue the commands easily and quickly
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4. We can transfer the cursor from one place to another easily and quickly
Disadvantages of Trackball
1. There is no facility to enter alphabets, numeric data
2. Mouse is a popular device to control pointer i.e., there is no need of trackball to control the
pointer
3. We cannot perform DOS operations properly
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VIDEO INPUT DEVICES
1. Scanner
2. Web camera
1. Scanner:
Scanner is used to scan photograph, images, documents etc. It acts like a photocopy
machine, except that instead of copying the image on to paper, it transfers the image directly into
the computer. Using scanner the hard copy images such as the image is on paper or a slide is
translated into electronic (digital) format that can be stored on computers. The scanner is an input
device attached to the computer by a cable and controlled by software. The result of scanned
image is a “bitmap file”.
Advantages of Scanner
1. It is a photocopy machine
2. We can transfer the existing data i.e., hard copy to the system
3. It may come in different models and styles
Disadvantage of scanner
1. There is no facility to enter alpha numeric data directly
2. It occupies more space than other input devices
3. There is no facility to transfer the cursor from one place to another place
4. There is no facility to control the mouse pointer
2. Web Camera:
Web camera is one of the input devices of a computer system. By using web camera we
can load various images into the computer and through this we can interact with different people
over the net.
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OUTPUT DEVICES
The output devices can display, print or plot the processed information. Output devices
can also generate sound, actions and graphics. The example of output devices are Visual Display
Units (V.D.U) i.e., monitors, printers, plotters, speech output unit etc.
MONITORS: -
This is the most commonly used output device on personal computer. The monitors are
used to produce output (processed information). There are two types of monitors used with PCs.
1. CRT (Cathode Ray Tube)
2. Flat Panel Monitors
All monitors can be categorized based on display colours. They are
1. Monochrome (Black and white) Monitors
2. Gray Scale Monitors
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3. Color Monitors
1. Monochrome Monitors:-
Monochrome monitor displays only one colour i.e., “White”. The background colour
of this type monitor is usually “Black”. These monitors are displays text only. Where the
user doesn’t see colour graphics.
2. Gray Scale Monitors:-
These monitors are display “Gray colour text, half-white background”. They are
used in low and portable systems (Especially hand held computers)
3. Colour Monitors:-
These monitors can display any where from 16 colours to 16 million colours. To day
most monitors are colour monitors.

EXPLAIN SOFTCOPY DEVICES (or) V. D. U (Visual Display Units)

A VDU is a television like device used to display input data or information, allowing user
to display the results of processing. Quality of monitor based on the resolution, which is a
measure number of pixels. A pixel is the smallest graphical element. According to resolution
Monitors are categorized into two types
1. CRT (Cathode Ray Tube )
2. Flat – Panel Display
CRT MONITORS:-
The CRT monitors displays the image with the help of phosphorus and chemical coating
and an electron gun. The gun shoots a beam of electrons through a magnetic coil, which aims
the beam at the front of the monitor. The back of the monitors screen is coated with
phosphorous, chemicals that glow when they are struck by the electron beam. The screen’s
phosphorous coating is organized into a grid of dots. The smallest number of phosphorous dots
that the gun can focus on is called a pixel. Each pixel has a unique address, which the computer
uses to locate the pixel and controls its appearance. CRT has display screen of 25 rows and 80
columns. It is used in most desktop computers.
In colour monitor the three guns represent the primary colours (RED, GREEN, BLUE),
In a colour monitor each pixel includes three phosphorous (RED, GREEN, BLUE) arrange in a
triangle. When the beams of each of three guns are combined and focused on a pixel, the
phosphorus light up. These monitors can display different colours by combining various
intensives of the three beams.
FLAT PANEL DISPLAY :-
A CRT monitor is reliable and a standard for used with desktop computers because they
provide brightest and clearest picture for relatively low cost. There are 2 major disadvantages
1. CRT monitors are big, they take up desktop space and difficult to move
2. CRT monitors requires a lot of power to run
There fore, they are not practical for use a notebook computer.
A thin and lightweight monitor is used in a computers, commonly used in laptop
computer is known as Flat Panel monitors. It does not have a picture tube. The flat panel
monitor creates an image through transistors. They are several types of flat panel monitors but
the most common type of flat panel display is used with Liquid Crystal Display (LCD). The
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LCD monitor creates images with a special kind of liquid crystal that normally transparent
(clearly) but becomes opaque when charge with electricity. Hand held calculators and digital
watches usually used liquid crystal displays. There are 2 main categories.
1. Passive matrix LCD
2. Active matrix LCD
1. Passive Matrix LCD :-
Passive matrix LCD depends on transistors per each row and column of pixels thus,
creating a grid that defines the location of each pixel. The colour displayed by a pixel is
determined by the electricity coming from the transistor at the end of the row and top of the
column. It doesn’t refresh the pixels very regularly. Animated graphics can appear clearly on a
passive matrix monitor.
2. Active Monitor LCD:-
This technology assigns a transistor to each pixel, and each pixel is turned on and off
individually. This enhancement allows the pixels to be refreshed much more quickly. Active
Matrix LCD uses thin-film transistors (TFT) technology which employees as many as 4
transistors per pixel so, it is also called as Thin Film Transistor.
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DIFFERENCE BETWEEN CRT AND FLAT PANEL MONITORS

CRT FLAT PANEL

1. CRT monitors are large size and 1. Flat panel monitors do not
occupy more area require a lot of desktop
2. They are heavy weight 2. They are light weight
3. They are less cost than flat panel 3. They are high cost than CRT
monitors monitors.
4. It operates with the help of 4. It operates with the help of
power supply batteries or power
5. It consists of an electronic gun 5. It consists of an transistors
6. CRT monitors creates an images 6. Flat panel monitors creates an
with the help of chemicals and image with the help of LCD
phosphorous. technology.
7. The viewable are of CRT 7. Flat panel monitors also
monitors ranges from 14 inches viewable area from 14 inches to
to 21 inches 18 inches
8. CRT monitors release low level 8. These type of monitors do not
radiation release any radiation
9. It consumes a great amount f 9. These monitors do not consume
electricity to keep the screen a lot of energy because they have
refreshed tiny transistors
10. Because the structure of these 10. Because the flat screen, do not
monitors, there will be twist the cause any twist in the picture.
picture and reducing the clarity.
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PC- PROJECTORS:-
The projector is an output device, which are used to display the images or colorful
presentations on a wall on the big screen. The PC projectors plugs into one computer ports, then
projects the video output on to an external surface, These small devices typically weightless and
display over 16 million colours. Some PC – Projectors can be converted from still video mode to
full video mode, to display output from a VCR or DVD drive.
Most PC-Projectors use LCD technology to create image. An LCD projector requires the
room to be darkened. They display image in low lighting conditions. Newer model Digital
Light Processing (DLP) technology projectors can display clear image in normal lighting
conditions. The DLP device contains digital micro mirror device, which controls the image
display.
SOUND SYSTEM:-
Microphones are now important input devices, and speakers and their associated
technology are the output systems. Today, when we buy a multimedia PC, we receive a machine
that includes a CD-ROM (DVD) drive, high quality video controller, speakers, and sound cards.
The speakers produce sound like a stereo. The only difference is that they are usually
smaller and they contain their own amplifiers. Otherwise, they do the some thing any speaker
does. They transfer a constantly changing electric current to a magnet, which pushes the speaker
cone back and forth. The moving speaker cone creates pressure vibrator in the air – in other
words sound.
The more complicated part of the sound output system is sound card. The sound card
translates digital sounds in to the electric current. i.e., send to the speakers. To digitize the
sound, the waves are converted to an electronic current i.e., measured thousands of time per
second and recorded as a series of numbers. When the sound is played back the sound card
reverse this process, translating the numbers into electric current i.e., send to the speakers.
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HARD COPY DEVICES:

Hard copy devices are used to produce”Hard Copies”. Printers are commonly called as
“Hard Copy Devices”.
PRINTERS:
Printers are most important output devices, which is used to print information on papers.
They are divided into two categories
1. Impact Printers
2. Non Impact Printers
IMPACT PRINTERS:
An impact Printers creates an image by using pins or hammers by pressing an inked
ribbon against the paper. A Simple example of an impact printer is a typewriter, which uses
small hammers to strike the ribbon. Each hammer is embossed with shape of a letter, number or
symbol. That shape is transferred through the inked ribbon on to the paper. Many modern
electric typewriters can be connected to PCs and used as a Letter Quality Printer.
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Ex: Dot Matrix Printer, Typewriter, electronic typewriter etc.,

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NON-IMPACT PRINTERS:
Non-Impact printers use chemicals, Lasers and heat to form the images on the paper. For
Example, Ink jet Printer used tiny nozzles to spray droplets of ink on to the page. Laser Printer
works like a photocopy
Ex: Ink-Jet Printers, Laser Printer etc.

DOT MATRIX PRINTERS:

(Describe a dot matrix printers creates an image on the page? or Have a dot matrix printer
creates an image on the page?)
A Dot Matrix Printers is common type of impact printer. These Printers are used to print
images on to the page or to print carbon copy. These printers can produce sheets of plain text very
quickly.
A Dot Matrix Printers creates an image by using a print head. The print head contains a
number of tiny pins. It prints the character or digits by putting group of dots on to the paper. Dot
matrix name implies that a single pin strikes the ribbon and single dot ink is printed on to the
page. Characters get printed as the head travel from left to right and in some cases it travels from
reverse direction as well.
The resolutions of the lowest Dot Matrix Printers have only 9 pins. The highest resolution
printers have 24 pins. The speed of this printer is measured in Character Per Second (CPS). The
Smallest Dot Matrix Printer Creates 50 to 70 CPS and the Fastest Dot Matrix Printer prints more
than 500 CPS. Dot Matrix Printers are not commonly used in homes. They are used in business.
The print quality of these printers is not fine.
Many impact printers can also sheet feed that is they can accept and print a single sheet
of paper. Some type of impact printers can use tractor feed papers (continuous feed papers)
Advantages:
 We can take sheet of plain text easily and quickly
 Maintenance cost is low compared to other printers
 In small organizations the dot matrix printer is commonly used
 We can take carbon copies, tractor feed papers (continuous) can used to take the printing using
dot matrix printer.
Dis-Advantages:
 We can take single colour printing using dot matrix
 It takes more time to print graphics
 Now a day it is not suitable for taking various types of printings
 Good quality printing is not available

INK JET PRINTERS:

Ink Jet or bubble jet Printers works in the same way as dot matrix printer. The difference
is that, A dot matrix printer creates an image by using a machine called a print head, Ink Jet
printers creates an image directly on the paper by spraying ink through tiny nozzles. No ribbon is
required. This printer can print from 2 to 4 pages per minute. The operating cost is very low when
compared to laser printer. Expensive maintenance is rare, and only part that needs routine
replacement is the Ink Cartridge. Many Ink Jet printers use only one cartridge for color printing
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and a separate black cartridge is used for blank and white printing. This feature saves money by
preserving coloured ink only for colour printing. The print quality is good than dot matrix printer.
But print quality is no good as laser printer.
MERITS
 Operating cost is low compared to laser
We can take colour graphics
 We can maintain various cartridges for printing various images
 Some times inkjet printer is called as four coloured printer(RED, BLUE,BLACK,YELLOW)
and it is used for printing color images
 We can take 20 – 30 copies/minute using inkjet printer
DEMERITS
 Operating cost is very high compared to dot matrix printer
 We can use only cut off sheets for printing
 Compared to laser, inkjet does not display quality images

LASER PRINTERS:
Laser printers are used to produce high quality images. These printers produce the image
like as a photocopier. As their name implies, a laser is at the heart of these printers. A separate
CPU and memory is built into the printer to print the data i.e., receives from the computer and to
control the laser. These printers are more expensive than inkjet printers, their print quality is
higher and printing is very fast. The quality and speed of laser printers that are used office
environments, where several users can easily share the same printers through a LAN.
The laser in a laser printer can aim at any point on a drum, creating an electrical charge
Toner. A color laser printer works like a single colour model except that the process is repeated 4
times and different toner colors are used for each pass. A colour laser printer used RED, BLUE,
BLACK, YELLOW colours. Single color (BLACK) laser printers typically can produce 4 to 16
pages of text a minute.
Finally, the maintenance cost of laser printer is high but print quality is very good.
Advantages:
 We can take good quality images using laser printer
 It has special CPU and memory for printing various images
 Laser is the heart of these printers
 Laser printers can produce 4 – 16 papers/minutes
 The resolution of laser printer is 1200 – 1800 dots/inch
Dis-Advantages:
 Operating cost is very high compared to other printers
 It takes more time to print colour images
 Only cut-off sheets are used to print an image
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PLOTTERS:
A plotter is special kind of out put device. It is like a printer because it produces images
on paper, but it is used to print large-format images, such as construction or engineering drawings.
Plotters are two types. They are
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1. Flatbed or Table plotters

2. Drum or Roller plotters
1. Flatbed or Table plotters:
The flatbed plotter is less expensive and is used in small computing systems. These
plotters are used to produce images with the help of two robotic arms. Each of this holds a set of
colored ink pens or pencils. The two arms are working performance operating at right angles as
they draw on a stationary piece of paper. These plotters are normally slow; they can take more
time to print complicated drawings.
2. Drum or Roller plotters:
The drum plotters are normally used with Mainframe computer system. It has only one
robotic arm, which moves side to side as the paper is rolled back and forth through roller. The
roller working together the arm and roller can draw perfect circles and other geometric shapes.
In recent years mechanical plotters have been produced the drawings very quickly and
the maintenance cost is very low compared to other plotters.
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MEMORY
A memory is required in a computer to store programs and data processed by the
programs. A memory is made up of a large number of cells, with each cell capable of store one
bit. The cells may be organized as a set of words, each word storing a sequence of bits.
The information and data are stored temporarily or permanently in the memory units of
computer system. These memory units are classified into two types. They are
1. Primary or Main memory
2. Secondary or Auxiliary memory
1. Primary Memory: -
This memory is also known as “Main Memory” or “Internal Memory”. We can store
data and instructions in primary memory temporally. The capacity of primary memory is
limited. When we switch off the computer it looses the information.
Primary memory is faster when compared to other memory devices. It is a costly device.
The currently needed programs and data to the C.P.U are stored in main memory. The primary
memory is further divided into two types. They are
1. Random Access Memory (RAM)
2. Read Only Memory (ROM)
1.Random Access Memory (RAM): -
This memory is also called “Read and Write” memory i.e., we can store, read or modify
and delete the contents in this memory. The data and instructions, which are store and remove
automatically from this memory. When the power goes off or switch off the computer it looses
the information stored in this memory. Hence it is known as “Volatile Memory”. The minimum
capacity of “RAM” in any computer is 640KB(Base memory)
RAM’S are divided into two types
1. Dynamic RAM (DRAM)
2. Static RAM (SRAM)s
I) Dynamic RAM:- The information stored in dynamic ram has to be refreshed after every few
milliseconds, otherwise it is erased. This RAM has higher storage capacity than Static Ram.
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ii) Static RAM: - The information stored in static ram need not be refreshed. But it remains
stable as long as power supply is provided.
3. Read Only Memory: - The information is stored in this memory is for read only
purpose. We cannot store or modify and delete the contents in this memory. At the
manufacturing time of this memory chip, the manufacturer will store the
information in this memory. These ROM chips are used in computer for storing
BIOS (Basic Input Output System) set up. When the power goes off or switch off
the computer does not loose any information. Hence it is known as “non-volatile”
memory.

This ROM’s are classified as follows

ROM

PROM EPROM EEPROM

i) PROM (Programmable Read Only Memory): -

A version of ROM that cannot be changed under normal circumstances that can be programmed
under special conditions is called PROM(Programmable Read Only Memory).
iii) EPROM (Erasable Programmable Read Only Memory): -
It is a developed version of PROM, which can be erasable by using ultraviolet rays. So,
we are calling it as EPROM (Erasable Programmable ROM)

(iv)EEPROM (Electrically Erasable Programmable Read Only Memory): - It is similar to

EPROM but using a high voltage current can erase its information.
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Write difference between RAM and ROM?