Fundamental of Computers
& Information Technology
Unit-II
Input Devices: - An input device
can be defined as an electromechanical device that allows the user to feed
information (data) into the computer for analysis, storage and to give commands
to the computer. Data and instructions are entered into the main memory of
computer through an input device. Input device captures information and
translates it into a form that can be processed and used by other parts of the
computer. After processing the input data, the computer provides the results
with the help of output devices. Input devices play a major role in the
processing of any data via the computer system because the output of the computer
is always based on the given input. A computer can accept input in two ways,
either manually or directly. In case of manual data entry, the user enters the
data into computer by hand such as by using keyboard and mouse. User can also
enter data directly by transferring information automatically from a source
document (like barcode) into the computer.
Keyboard: - Keyboard
devices are the most commonly used input devices today. Using a keyboard, the
user can type text and execute commands. Keyboard is designed to resemble a
regular typewriter with a few additional keys. Data is entered into the
computer by simply pressing various keys. The layout of a keyboard come in
various styles such as QWERTY, DVORAK, AZERTY but the most common layout is the
QWERTY. It is named so because the first six keys on the top row of letters are
Q, W, E, R, T and Y. The number of keys on a typical keyboard varies from 82
keys to 108 keys. Portable computers such as laptops quite often have custom
keyboards that have slightly different key arrangements than a standard
keyboard.
Keyboard is the easiest input device, as it does not
require any special skill. Usually, it is supplied with a computer so no
additional cost is incurred. The maintenance and operation cost of keyboard is
also less.
Layout of the keyboard:- The layout of
the keyboard can be divided into the following five sections:
- Typing Keys(Alphanumeric Keys):- The
alphanumeric keys contain the keys for the letters of English alphabet,
the numbers 0 to 9, and several special characters like ?, /, $, &
etc.
- Numeric Keypad:- The numeric keypad is a set of
keys that looks like an adding machine with its ten digits and
mathematical operators(+, -, * and /). It is usually located on the right
side of the keyboard.
- Functions Keys:- The function keys (F1, F2, F3
etc) are arranged in a row along the top of the keyboard and could be
assigned specific commands by the current applications or the operating
system. For example, most of the Microsoft programs use F1 to display
helps.
- Control Keys:- These keys provides cursor and
screen control. It includes four directional arrow keys that are arranged
in an inverted T formation between the typing keys and the numeric keypad.
These keys allow the user to move the cursor on the display area one space
at a time. In either an up, down, left or right direction. Control keys
also include Home, End, Insert, Delete, Page up, Page Down, Control(Ctrl),
Alternate(Alt) and Escape(Esc). The Windows keyboard also consists of two
Windows or Start keys, and an Application key.
- Special Purpose Keys:- A keyboard also contains
some special purpose keys such as Enter, Shift, Caps Lock, Num Lock,
Spacebar, Tab and Print Screen.
Working of a Keyboard:- A keyboard is
a series of switches connected to a small keyboard microprocessor that monitors
the state of each switch and initiates a specific response to a change in that
state. When the user presses a key, it causes a change in the amount of current
flowing through the circuit associated specifically with that key. The keyboard
microprocessor detects this change in current flow. By doing this, the
processor can tell when a key has been pressed and when it is being released.
Depending upon which key’s circuit carries a signal to the microprocessor, the
processor generates the associative code, known as scan code, of the key and
sends it to the operating system. A copy of this code is also stored in the
keyboard’s memory. When the operating system reads the scan code, it informs
the same to the keyboard and the scan code stored in keyboard’s memory is then
erased. Initially, the processor filters all the tiny current fluctuations out
of the signal and treats it as a single key press. If the user continues to
hold down a key, the processor determines that he wish to send that character
repeatedly to the computer. In this process, the delay between each instance of
a character can normally be set in operating system, typically ranging from 2
to 30 characters per second(cps).
Keyboard Buffer:- A keyboard buffer
is a small memory inside either the terminal or the keyboard in which each
keystroke is first saved before being transferred to the computer’s main memory
for processing. The keyboard buffer usually has capacity to save from a few
tens to a few hundreds of keystrokes. Storing of keystrokes in keyboard buffer
instead of sending them directly to the main memory makes the user interaction
with the system much more efficient and smooth. This is because when the
keystroke is made, the processor may be busy doing something else and may not
be in a position to immediately transfer the keyboard input to the main memory.
Pointing Devices:- Most computers
come with an alphanumeric keyboard but in some applications, keyboard is not
convenient. For example, if the user wants to select an item from a list, the
user can identify that items position by selecting it through the keyboard.
However, this action could be performed quickly by pointing devices. A pointing
device is used to communicate with the computer by pointing to locations on the
monitor screen. Some of the commonly used pointing devices are mouse,
trackball, joystick, light pen and touch screen.
Mouse:- Mouse is a small
hand held pointing device. Usually a mouse contains two or three buttons, which
can be used to input commands or information. The mouse may be classified as a
mechanical mouse or an optical mouse. A mechanical mouse uses a rubber ball at
the bottom surface, which rotates as the mouse is moved along a flat surface,
to move the cursor. Mechanical mouse is the most common and least expensive
pointing device. Microsoft, IBM and Logitech are some well-known makers of the
mechanical mouse.
An optical mouse uses a light beam instead of a rotating
ball to detect movement across a specially patterned mouse pad. As the user
rolls the mouse on a flat surface, the cursor on the screen also moves in the
direction of mouse’s movement. An optical mouse has the following benefits over
the mechanical mouse:
- No moving part means less wear and a lower
chance of failure.
- Dirt can not get inside the mouse and hence no
interference with the tracking sensors.
- They do not require a special surface such as a
mouse pad.
Depending on the
application, the cursor of the mouse can be text cursor or graphic cursor. The
text cursor (I) is used for text while the graphic cursor is used for pointing
and drawing. The graphic cursor is displayed on the screen by the variety of
symbols such as arrow or a pointing finger.
Like keyboard, usually it is also supplied with a
computer; therefore, no additional cost is incurred. However, it needs a flat space
close to the computer. The mouse can not easily be used with laptop, notebook
or palmtop computers.
Some of the common mouse
actions are: Pointing, Click, Right Click, Double Click and Drag and Drop.
Working of a Mouse:- Principally,
the mouse works by measuring how much it moves in a given direction. A
mechanical mouse has a rubber ball in the bottom. When the user moves the
mouse, the balls rolls along the surface of the mouse pad, and the mouse keeps
track of how far the balls rolls. This allows it to tell how far it has moved.
Inside the bottom of the mouse are three rollers. One of them, the one mounted
at a 450 angle to the other two, is spring loaded. This
roller is usually the smallest of the three. It is there simply to hold the
ball against the other two rollers. The other two rollers are usually larger
and of different color. These rollers are mounted at a 900 angle to
the one other, one roller measures how fast the ball is turning horizontally
and the other measures how fast it is turning vertically. When the ball rolls, it turns these two rollers. The
rollers are connected to axles and the axles are connected to a small sensor
that measures how fast the axle is turning. Both sets of information are passed to the electronics
inside the mouse. This little processor, usually consisting of little more than
a single chip, uses the information to
determine how fast the mouse itself is moving, and in what direction. This
information is passed to the computer via mouse cord, where the operating system
then moves the pointer accordingly.
The optical mouse uses an infrared light and special
mouse pads with fine grid lines to measure the rotation of the axle. The axle
in optical mouse is connected to a little photo-interrupter wheel with a number
of tiny holes in it. in front of this wheel is a light and on the other side of
the wheel is a light metre. As the wheel
turns, the light flashes through the holes in the wheel. By measuring
how often these flashes occur, the light sensor can measure how fast the wheel
is turning and sends the corresponding coordinates to the computer. The
computer moves the cursor on the screen based on the coordinates received from
the mouse. This happens hundreds of times each second, making the cursor appear
to move very smoothly.
Trackball:- A trackball is a pointing device that is
similar to a mechanical mouse. The ball that is placed in the base of a
mechanical mouse is placed on the top along with the buttons in case of a
trackball. To move the graphics cursor around the screen, the ball is rolled
with the fingers. Because the whole device is not moved for moving the graphics
cursor, a trackball requires less space than a mouse for operation. Since it
need not be moved for moving the graphics cursor, it is often attached to or
built into the keyboard. Trackball built into the keyboard are commonly used in
laptop and notebook computers because a mouse is not practical for laptop users
in a small space. A trackball comes in various shapes and forms with the same functionality. The three commonly used shapes are a ball, a
button, and a square. In case of a ball, the ball is rolled with the help of
fingers to move the graphics cursor. In case of a button, the button is pushed
with a finger in the desired direction of the graphics cursor movement. In case of a square plastic, the fingers is
placed on top of it and moved in the desired direction of the graphics cursor
movement.
Working of a trackball:- A trackball
works in the same way as a mouse, with the ball turning rollers, the rollers
turning axles(axis) , which are in turn connected to either mechanical or
optical sensors that measure their rotation. A trackball consists of a number
of components. As one moves the trackball, it starts a chain of events inside the
box that results in the pointer moving on the computer screen. In a normal
trackball, on one side of each encoding wheel is a pair of LED(light emitting
diode) that emits infrared light. On the opposite side of each pair of LEDs,
there is a light sensor. Every time light from the LEDs shines through a hole
in the encoding wheel, a pulse of electricity is sent from the light sensor to
the microprocessor. When the trackball rolls side-to-side, the horizontal
(x-axis) shaft rotates, spinning the attached encoder wheel. Similarly, when
the trackball is rolled up and down, the vertical (y-axis) shaft rotates,
spinning the attached encoder wheel. Due to this spinning(rotating), the light
blinks which can be detected by the light sensor. The microprocessor counts how
many times the light sensors detect light each second and send this information
to the computer along the cord.
Joystick:- A joystick is
a pointing device that works on the same principle as a trackball. Instead of
using the fingers in case of a trackball, the user of a joystick moves the
spherical ball with the help of the stick with his/her hand. The stick can be
moved forward or backward, left or right, to move and position the graphics
cursor at the desired position. The joystick offers three types of control:
digital, glide and direct. Digital control allows movement in a limited number
of directions such as up, down, left and right. Glide and direct control allow
movements in all directions (360 degrees). Direct control joysticks have the
added ability to respond to the distance and speed with which the user moves
the stick.
The basic design of a joystick consists of a stick that
is attached to a plastic base with a flexible rubber sheath. This plastic base
houses a circuit board that sits beneath the stick. Joysticks are mainly used
for computer games, for other applications, which includes flight simulators,
training simulators, CAD/CAM systems, and for controlling industrial robots.
Working of a Joystick:- Various joystick technologies are available
and they differ mainly in how much information they pass on. All the joysticks
are designed to inform the computer about the positioning of the handle at any
given time. This is done by providing the x-y coordinates of the handle. The
x-axis represents the side-to-side position and the y-axis represents the
forward block position. This basic design consists of a stick that is attached
to a plastic base with a flexible rubber sheath. The base houses a circuit
board that sits directly underneath the stick, which carry electricity from one
contact point to another. When the joystick is in the neutral position, all but
one of the individual circuits are
broken. Each broken section is covered with a simple plastic button containing
a tiny metal disc. When the stick is moved in any direction, it pushes down on
one of these buttons, pressing the conductive metal disc against the circuit
board. This closes the circuit, that is, it completes the connection between
the two wire sections. When the circuit is closed , electricity can flow down a
wire from the computer and to another wire leading back to the computer. When
the computer picks up a charge on a particular wire, it knows that the joystick
is in the right position to complete that particular circuit. The joystick
buttons work exactly the same way. When a button is pressed down, it completes
a circuit and the computer recognizes a command.
Digitizing Tablet:- A digitizer is an input device used for
converting(digitizing) pictures, maps, and drawings into digital form for
storage in computers. For example, the x and y coordinates of points in a
drawing may be stored in digital form. this enables re-creation of the drawing
from the stored information whenever required as well as easy of changes in the
drawing as and when required.
A digitizer consists of a digitizing tablet(also known as
graphics tablet) associated with a stylus. The digitizing tablet is a flat
surface that contains hundreds of fine copper wires forming a grid. Each copper
wire receives electric pulses. The digitizing tablet can be spread over a
working table and is connected to a computer. The stylus is like a pen or a
lens-like cursor with a cross-hair and button. The stylus is connected to the
tablet and can be pressed down at a point on the tablet to input the (x, y)
coordinates of the point. When the stylus is moved on the tablet, the cursor on
the computer’s screen moves simultaneously to a corresponding position on the
screen to provide visual feedback to the operator. This enables the operator to
draw sketches directly or to input sketched drawings very easily. Inputting
drawings or developing sketches using a digitizer is further simplified by the
fact that poorly sketched lines, arcs, and other graphical objects are
automatically input as mathematically precise objects, like straight lines and
smooth curves. Digitizer are commonly used in the area of Computer Aided Design(CAD) by architects and engineers
to design cars, buildings, medical devices, robots, mechanical parts, etc. They
are also used in the area of Geographical Information System(GIS) for
digitizing of maps available in paper form.
Scanners:- There are a
number of situations when some information (picture or text) is available on
paper and is needed on the computer disk for further manipulation. An scanner
is an input device that translates paper documents into an electronic format
that can be stored in a computer. The input documents may be typed text,
pictures, graphics or even handwritten material. This input device has been
found to be very useful in preserving paper documents in electronic form. The
copy of a document stored in a computer in this manner will never deteriorate
in quality or become yellow with age and can be displayed or printed whenever
desired. If the computer in which the scanned document is stored has the right
kind of software, the stored images can be altered and manipulated in
interesting ways.
Scanners are also called optical scanners because they
use optical technology for converting an image into electronic form. They can
store images in both gray-scale and color mode. The two most common types of
scanners are hand-held scanner and flat-bed scanner.
Hand-Held Scanner:- A hand-held
scanner consists of light emitting diodes, which are placed over the material
to be scanned. This scanner performs the scanning of the document very slowly
from the top of the bottom, with its light on. In this process, all the
documents are converted and then stored as an image. While working, the scanner
is dragged very steadily(gradually) and carefully over the document and it
should move at a constant speed without stopping or jerking in order to obtain
best results. Due to this reason, hand
held scanners are widely used where high accuracy is not of much importance.
The size of hand held scanners is small. They come in various resolution, up to
about 800 dpi (dots per inch) and are available in either grey scale or colour.
Furthermore, they are also used when the volume of the documents to be scanned
is low. The typical application of this scanner include the storing and
reproducing of the images in publications. These devices read the data on the
price tags, shipping labels, inventory part number, and so on.
Working of a hand-held
scanner:- When the hand-held scanner’s scan button is pressed, a light
emitting diode illuminates the document underneath it. An inverted angled
mirror directly over the scanner’s window reflects the image onto the scanner’s
lens, which is located at the back of the scanner. The lens focuses a single
line of the image onto a charged coupled device(CCD), which contains a row of
light detectors. As the light shines through these detectors, each of them
records the amount of light as a voltage that corresponds to white, black, grey
or to a colour. These voltages are sent to a specialized analog chip, which
corrects any colour detections error. After that, a single line image is passed
to analog to digital converter(ADC), which converts the analog signals into
binary form that can be sent to the computer. In this way, the converter clears
itself of the data so that it can receive the next line of the image.
Flat-Bed Scanner:- Flat-bed scanners look similar to a
photocopier machine. It consists of a box containing a glass plate on its top
and a lid that covers the glass plate. This glass plate is primarily used for
placing the document to be scanned. The light beam is placed below the glass
plate and when it is activated, it moves from left to right horizontally. After
scanning one line, the beam of light moves in order to scan the next line and
thus, the procedure is repeated until all the lines are scanned. For scanning,
an A4 size document takes about 20 seconds. These scanners are capable of
scanning black and white as well as colour images. The flat-bed scanners are
larger in size and more expensive than the hand-held scanners. However, they
usually produce better quality images because they employ better scanning
technology.
Working of a flat-bed
scanner:- To scan a document, first it is placed on the glass plate and the
cover is closed. A lamp is used to illuminate the document. The scan head
(mirrors, lens, filter and CCD array constitutes a scan head) is moved slowly
across the document by a belt that is attached to a stepper motor. The head is
attached to a stabilizer bar to ensure that there is no wobble (vibrate) or
deviation in the pass. In scanning
terms, a pass means that the scan head has completed a single complete scan of
the document. The image of the document is reflected by an angled mirror to
another mirror. Each mirror is slightly curved to focus the image it reflects
onto a smaller surface. The last mirror reflects the image onto a lens. The
lens focuses the image through a filter on the CCD array. It is a collection of
tiny light-sensitive diodes(also called photo sites), which converts light into
electrical charge. The brighter the light that hits a single photo site, the
greater the electrical charge that will accumulate at that site. Some scanners
use a three pass scanning method. Each pass uses a different colour filter(red,
green or blue) between the lens and CCD array. After the three passes are
completed, the scanner software assembles the three filtered images into a
single full-colour image. Nowadays, most scanners use the single pass method.
The lens splits the image into three smaller versions of the original image.
Each smaller version passes through a colour filter(either red, green, blue)
onto a discrete section of the CCD array. The scanner combines the data from
the three parts of the CCD array into a single full-colour image, which is then
sent to the computer.
Digital Camera:-Digital camera
stores images digitally rather than recording them on a film. Once a picture
has been taken, it can be downloaded to a computer system and then manipulated
with an image editing software and printed. The big advantage of digital
cameras is that making photos is both inexpensive and fast because there is no
film processing.
Working of a digital camera:- All digital cameras
record images in an electronic form, that is, the image is represented in
computer’s languages, the language of bits and bytes. Essentially, a digital
image is just a long string of 1’s and 0’s that represent all the tiny colored
dots or pixels that collectively make up the image. Just like a conventional camera, it has a series of
lenses that focus light to create an image of a scene. However, instead of
focusing this light onto a piece of film, it focuses it onto a semiconductor
device that records light electronically. A computer then breaks this
electronic information down into digital data. The key difference between a
digital camera and a film-based camera is that the digital camera does not have
a film, instead, it has a sensor that converts light into electrical charges.
The image sensor employed by most digital cameras is a charge-coupled
device(CCD). Some low-end cameras use complementary metal oxide semiconductor
(CMOS) technology. The CCD is a collection of tiny light sensitive diodes, which
convert photons (light) into electrons (electrical charges).
MICR:- MICR is the interpretation by a computer of a line of characters
written in a special magnetic ink . these characters can be read by humans as
well .for instance there are a line of numbers and some odd-shaped characters
on the bottom of banks cheques . these magnetic ink characters are bank
processing symbols representing the cheque number customer account number and
bank identification number .when the bank receiver the cheque the amount of the
cheque is also printed in magnetic ink .these cheque are sent through a MICR
reader to interpret the information update the appropriate accounts and in some
cases ,sort the cheques afterwards
OCR:- This is the most sophisticated type of optical
recognition .an optical card reader works in much the same ways as the human
eye . it recognizes specially shaped numeric and alphabetic characters.
A set of optical characters may be used to print
merchandise tags that can be read using an OCR Reader to process the sales
transaction , the information on the tag such as item price and the inventory
number can be automatically entered at a point of sale terminal .pertinent data
can be saved and transferred to the company’s main computer system to be used
in activities such as managing inventories and analyzing sales .
OMR:- It employs marks sensing to scan and translate ,based on its
location which is a series of pen or pencil marks into computer readable form .
for instance the objective type multiple choice question paper we get in the
bank recruitment exam .A computerized optical mark reader scores the tests by
identifying the position of the mark
BCR:- The meaning of the BCR is also explained earlier. Till
now you might have got some idea about the acronym, abbreviation or meaning
of BCR. You might also like
some similar terms related to BCR to know more about it. This site
contains various terms related to bank, Insurance companies, Automobiles,
Finance, Mobile phones, software, computers, Travelling, School, Colleges,
Studies, Health and other terms.
Quick Response Code (QR Code):-A QR code (abbreviated from Quick Response
code) is a type of matrix barcode (or two-dimensional barcode)
first designed in 1994 for the automotive industry in Japan. A barcode is a
machine-readable optical label that contains information about the item to
which it is attached. In practice, QR codes often contain data for a locator, identifier,
or tracker that points to a
website or application. A QR code uses four standardized encoding modes
(numeric, alphanumeric, byte/binary, and kanji) to store
data efficiently; extensions may also be used.[1]
The Quick Response system became popular outside the
automotive industry due to its fast readability and greater storage capacity
compared to standard UPC barcodes. Applications include product tracking,
item identification, time tracking, document management, and general marketing.[2]
A QR code consists of black squares arranged in a square
grid on a white background, which can be read by an imaging device such as a
camera, and processed using Reed–Solomon error correction until
the image can be appropriately interpreted. The required data is then extracted
from patterns that are present in both horizontal and vertical components of
the image.[2]
Voice Recognition:- Voice recognition
software on computers requires that analog audio be converted into digital signals,
known as analog-to-digital conversion. For a computer to decipher a
signal, it must have a digital database, or vocabulary, of words or syllables,
as well as a speedy means for comparing this data to signals. The speech
patterns are stored on the hard drive and loaded into memory when the program
is run. A comparator checks these stored patterns against the output of
the A/D converter -- an action called pattern recognition
Light Pen:- A light pen is also a pointing device like mouse . it can be used to
choose a displayed menu option. The pen contains a photocell placed in a small
tube . As the user moves the trip of the pen over the surface of the screen,
its detects the light coming from a limited field of view the light from the screen
causes the photocell to respond and this electric response is transmitted to
the process which can identify the menu option that is triggering the
photocell. Light pen is useful for graphics work especially for computer aided
design (CAD)purposes.
Touch Screen:-
A touchscreen, is both an input and output device and normally
layered on the top of an electronic visual display of an information
processing system The display is often
an LCD or OLED display while the system is usually a
laptop, tablet or smartphone. A user can give input or control the
information processing system through simple or multi-touch gestures
by touching the screen with a special stylus or one or more fingers.[1] Some
touchscreens use ordinary or specially coated gloves to work while others may
only work using a special stylus or pen. The user can use
Output Devices
Monitor – Monitors are
the most popular output devices used today for producing soft-copy output. A
monitor is usually associated with a keyboard and together they form a video
display terminal(VDT). A VDT is the most popular input/output device used with
today’s computers. The name terminal comes from the fact that a terminal is at
the terminal or end, point of a communication path. The term monitor usually
refers to the entire box, whereas display screen can mean just the screen. In
addition, the term monitor often implies graphics capabilities.
There are many ways to classify monitors. The Most basic
is in terms of color capabilities, which separates monitors into three classes:
Monochrome – Monochrome
monitors actually display two colors, one for the background and one for the
foreground. The colors can be black and white, green and black or amber and
black.
Gray-scale – A gray-scale
monitor is a special type of monochrome monitor capable of displaying different
shades of gray. The use of many shades of gray to represent an image is called
gray scaling. Continuous-tone images, such as black and white photographs, use
an almost unlimited number of shades of gray. Conventional computer hardware
and software can only represent a limited number of shades of gray (typically
16 or 256). Gray scaling is the process of converting a continuous –tone image
to an image that a computer can manipulate.
Color – Color monitors
can display anywhere from 16 to over 1 million different colors. Color monitors
are sometimes called RGB monitors because they accept separate signals – red,
green and blue.
After this classification, the most important aspect of a
monitor is its screen size. Like televisions, screen sizes are measured in
diagonal inches, the distance from one corner to the opposite corner
diagonally. A typical size for small VGA monitors is 14 inches. Monitors that
are 16 or more inches diagonally are often called full-page monitors. The
screen size is sometimes misleading because there is always an area around the
edge of the screen that can’t be used. Therefore, monitor manufacturer must now
also state the viewable area – that is the area of screen that is actually
used.
Another way of classifying monitors is in terms of the
type of signal they accept: analog or digital. Nearly all-modern monitors
accept analog signals, which is required by the VGA, SVGA and other
high-resolution color standards.
Clarity of picture on a
screen – Screen clarity depends on three qualities: resolution, dot pitch and
refresh rate.
Resolution – It refers to
the sharpness and clarity of an image. The term is most often used to describe
monitors, printers and bit-mapped graphic images. For graphics monitors, the
screen resolution signifies the number of dots (pixels) on the entire screen.
For example, a 640-by-480-pixel screen is capable of displaying 640 distinct dots
on each of 480 lines, or about 300,000 pixels. This translates into different
dpi measurements depending on the size of the screen. For example, a 15-inch
VGA monitor (640*480) displays about 50 dots per inch.
Dot Pitch – Dot pitch is
the amount of space between pixels, the closer the dots, and the crisper the
image. This is a measurement that indicates the diagonal distance between
like-colored phosphor dots on a display screen. Measured in millimeters, the
dot pitch is one of the principal characteristics that determine the quality of
display monitors. The dot pitch of color monitors for personal computers ranges
from about 0.15 mm to 0.30 mm.
Refresh Rate – Refresh rate
is the number of times per second that the pixels are recharged so that their
glow remains bright. The refresh rate for a monitor is measured in hertz (Hz)
and is also called the vertical frequency; vertical scans rate, frame rate or
vertical refresh rate. The old standard for monitor refresh rates was 60 Hz,
but a new standard developed by VESA sets the refresh rate at 75 Hz for
monitors displaying resolutions of 640*480 or greater. This means that the
monitor redraws the display 75 times per second.
Interlacing – A display
technique that enables a monitor to provide more resolution inexpensively. With
interlacing monitors, the electron guns draw only half the horizontal lines
with each pass (for example, all odd lines on one pass and all even lines on
the next pass). Because an interlacing monitor refreshes only half the lines at
one time, it can display twice as many lines per refresh cycle. Another way of looking at it is that
interlacing provides the same resolution as non-interlacing but less
expensively. A shortcoming of interlacing is that the reaction time is slower,
so programs that depend on quick refresh rate (for example, animation and
video) may experience flickering or streaking.
Video Display Adapters – To display
graphics, a display screen must have a video display adapter. A video display
adapter also called a graphics adapter card is a circuit board that determines
the resolution, number of colors, and how fast images appear on the display
screen. Video display adapters come with their own memory chips, which
determine how fast the card processes images and how many colors it can display.
The video display adapter is often built into the motherboard, although it may
also be an expansion card that plugs into an expansion slot.
VGA – VGA stands for
Video Graphics Adapter, a graphics display systems for PCs developed by IBM.
VGA has become one of the de facto standards for PCs. In text mode, VGA systems
provide resolutions of 720 by 400 pixels. In graphics mode, the resolution is
either 640 by 480 (with 16 colors) or 320 by 200 (with 256 colors).
Since its introduction in 1987, several other
standards have been developed that offer greater resolution and more colors
(SVGA, XGA) but VGA remains the lowest common denominator. All PCs made today
support VGA and possibly some other more advanced standard.
SVGA – Short for super
VGA, a set of graphics standards designed to offer greater resolution than VGA.
There are several varieties of SVGA, each providing a different resolution:
800 by 600 pixels
1024 by 768 pixels
1280 by 1024 pixels
1600 by 1200 pixels
All SVGA standards support a
palette of 16 million colors, but the number of colors that can be displayed
simultaneously is limited by the amount of video memory installed in a system.
One SVGA system might display only 256 simultaneous colors while another
display the entire palette of 16 million colors.
XGA: Short for
extended graphics array, a high-resolution graphics standard introduced by IBM
in 1990. XGA was designed to replace the older 8514/A video standard. It
provides the same resolutions (640 by 480 or 1024 by 768 pixels), but supports
more simultaneous colors. In addition,
XGA allows monitors to be non-interlaced.
For any of these displays to
work video display adapters and monitors must be compatible. Your computers
software and the video display adapter must also be compatible.
Printers:- Printers
can be divided into two distinct categories on the basis of producing
impression over the paper:
1 Impact Printers
2 Non-impact Printers
Impact
Printers:- In impact printer, a character is printed on
the paper through physical contact between the print head and paper. Either the
needle or a character is stuck on the paper through the ribbon. This creates a
lot of noise when these printers work. Impact printers may also be categorized
into two types on the basis of produced (impression) pattern.
1 Solid Font:- In a solid font printer, a complete character
strikes a carbon ribbon or other inked surface against paper to produce an
image of the character.
2 Dot Matrix:- Dot matrix printer has a set of printing needles
or pins. Selected print needles strike the inked ribbon against paper to
produce an image of the character.
Impact
Printers can further be categorized into two
categories:
Character Printer :Character
printer prints character by character. It may work on both technologies: Dot
Matrix as well as Solid Font.
Line Printer :Line
printer prints one complete line at a time. It works on both the technologies :
Dot Matrix and Solid Font. Dot matrix type line printers are relatively slower
than solid font impact line printers. Speed may be 300 lines per minute or
more.
Dot
Matrix Printer:- DMP is the oldest
printing technology and it prints one character at a time. Usually, DMP can
print any shape of character, which a user can specify. In a dot matrix
printer, the character is formed with closely packed dots. The printing head
contains a vertical array of pins. Formation of character is done by the
movement of head across the paper. Selected print needles strike the inked
ribbon against paper to produce an image of the character. Dot matrix printer
supports printing of graphics. The speed of dot matrix printers is measured in
characters per second(cps). It is faster than daisy wheel printer and the
printing speed lies between 30 to 600 cps. The print quality is determined by
the number of pins. It comes in two print head specifications, 9 pin and 24
pin. The more pins per inch, the higher the print resolution. Most DMP printers
have a resolution ranging from 72-360 dpi. DMPs are inexpensive and have low
operating costs. The major limitation of DMP is that it prints only in black
and white. They can handle applications such as accounting, personnel, and
payroll very well.
Examples are EPSON EX, 1000, EPSON LQ 1050, CITIZEN MSP 55, GODREJ, etc.
Working
of A DMP:- The
technology behind dot matrix printing is quite simple. The paper is pressed
against a drum and is intermittently(from time to time) pulled forward as printing progresses. The
printer consists of an electro-magnetically driven print head, which is made up
of numerous print wires(pins). The characters are formed by moving the
electro-magnetically driven print head across the paper, which strikes the
printer ribbon situated between the paper and print head pin. As the head
stamps onto the paper through the inked ribbon, a character is produced that is
made up of these dots. These dots seem to be very small for the normal vision
and appear like solid human-readable characters.
Daisy
Wheel Printer :- It is a solid font type character printer.
Daisy wheel printer is named as such because the print head resembles a daisy
flower, with the printing arms appearing like the petals of the flower. Speed
lies between 30 cps to 90 cps. Print quality is better than dot matrix. It is a
bi-directional printer, i.e. the head of the printer prints while moving in
forward direction as well as in backward direction. It also supports graphics
such as curves which can also be produced.
Daisy wheel printer is a letter quality
printer because it produces solid characters unlike broken characters formed by
a dot matrix printer. The font (i.e. style of character) is of fixed type for a
Daisy Wheel printer.
Working
of a Daisy Wheel Printer:- These
printer have print heads composed of metallic or plastic wheels. A raised
character is placed on the top of each of the daisy wheels petals. Each petal
has an appearance of a letter, number of punctuation mark on it. To print wheel is rotated around until the
desired character is under the print hammer. The petal is then struck from behind
by the print hammer, which strikes the character, pushing it against the ink
ribbon, and onto the paper, creating the character.
Line
Printers:- Line printers are high-speed printers capable of printing an entire line
at one time. A fast line printer can print as many as 3000 lines per minute.
The disadvantage of line printers are that they can print only one font, they
can not print graphics, the print quality is low, and they are very noisy.
Non-impact Printers:-
In Non-impact
printers, the head does not come directly in contact with the paper. There is
no impact or hitting of needles so non-impact printers don't make any noise
while printing. They come in many of varieties:
1 Thermal printer
2 Laser printer
3 Ink Jet printer
4 Electrostatic printer
5 Electro graphic printer
Thermal
Printer:- In a thermal printer the characters are
formed by pressing an array of electrically heated needles against heat
sensitive paper. Such papers have a special heat sensitive coating which
becomes dark when a spot is heated. Character is printed with a matrix of dots
which are heated by the needles.
It is not possible to produce multiple copies simultaneously with this
type of printer. A special type of paper is used with this printer which is
costly. This has reduced the popularity of thermal printers.
Laser
Printer:- A laser printer provides the highest quality
text and images for personal computers today. It is a very fast printer, which
operates on the same principle as that of a photocopy machine. Most laser printers
can print text and graphics with a very high quality resolution. Laser printer
works on the concept of using laser beams to create an image on a
photosensitive surface. Initially the desired output image is written on a
copier drum with a laser beam that operates under the control of the computer.
The laser exposed drum areas attract a toner that attaches itself to the
laser-generated charges on the drum. The toner is permanently fused on paper
with heat and/or pressure by rolling the drum over the blank paper. Laser
printers are quiet and produce very high quality of output. They are capable of
printing 4-30 pages per minute. Laser printers are often faster than ink-jet
printers, but are more expensive to buy and maintain than the other printers.
The cost of these printers depends on a combination of costs of paper, toner
replacement, and drum replacement. These printers are useful for volume
printing because of their speed.
Working
of a laser printer:- The
core component of laser printing system is the photoreceptor drum. A rotating
mirror inside the printer causes the beam of a laser to sweep across the
photoconductive drum. Initially, the beam of laser charges the photoconductive
drum positively. When the charged photoconductor is exposed to an optical image
through a beam of light to discharge, a latent or invisible image is formed. At
the point where the laser strikes the surface of drum, it creates a dot of
positive charge. These points are represented by a black dot, which will be
printed on the paper. After this, the printer coats the drum with a container,
which contains a black powder called toner. This toner is negatively charged,
and so it clings to the positive areas of the drum surface. When the powder
pattern gets fixed, the drum is rotated and the paper is fed into the drum
surface via a pressure roller. This pressure roller transfers the black toner
onto the paper. Since the paper is moving at the same speed as the drum, the
paper picks up the image pattern precisely. Finally, the printer passes the
paper through the fuser, a pair of heated rollers. As the paper passes through
these rollers, the loose toner powder gets melted and fuses with the fibers in
the paper. The paper is then brought out of the printer.
Ink Jet Printers:- The most common
type of printer found in homes today is the ink-jet printer. Ink Jet printers
use dot matrix approach to print text and graphics. Nozzles in the print head
produce tiny ink droplets. These droplets are charged which are deflected and
then directed to the desired spots on the paper to form the impression of a
character. It has a speed of 40-300 cps (character per second) with software
controls on size and style of characters. These printers support colour
printing and are very quiet and noiseless in operation. The print quality of
such printers is very near letter-quality. These printers are costlier than the
dot matrix printers, but the quality is much better. Ink-jet printers typically
print with a resolution of 600 dpi or more. They are also affordable, which
appeals to small businesses and home offices. These printer can print about 6
pages a minute.
Working of an Ink-Jet
Printer:-
An ink-jet printer has a print cartridge with a series of tiny electrically
heated chambers. These cartridges are attached to print heads with a series of
small nozzles that spray ink onto the surface of the paper. As printer head
moves back and forth across the page, software gives instruction regarding the
type and the quantity of colors. It also tells the position where the dots of
ink should be sprayed. There are two main ways to drop the ink droplets,
namely, the bubble-jet and piezo-electric technology.
Bubble-jet printers use heat to fire ink onto the paper.
There are three main stages with this method. The squirit is initiated by
heating the ink to create a bubble until the pressure forces it to burst and
hit the paper. The bubble then collapse as the element cools, and the resulting
vacuum draws ink from the reservoir to replace the ink that was ejected.
Piezo-electric technology uses a piezo crystal at the
back of the ink reservoir. It flexes when an electric current flows through it.
therefore, whenever a dot is required, a current is applied to the piezo
element, the element contracts and in doing so forces a drop of ink out of the
nozzle.
Electrostatic Printers :- An electrostatic
printer moves a continuous sheet of paper over the printing pins which put
small electric charges on the paper. The paper is then passed through a bath of
oppositely charged toner particles. As the opposite charges attract, the paper
picks up the toner on the spots charged by the print pins. The paper is then
passed through the fusing process and the toner is melted onto the paper to
form the character impression. Some electrostatic printers print up to 5000
lines per minute. Such printers use dot-matrix approach for printing. The print
head contains a vertical array (i.e. a vertical column) of pins. Such printers
can also produce graphics.
Comparative
View of Printers:
Printer
Type Advantages Disadvantages
Dot
Matrix Inexpensive, fast,
prints graphics Poor quality
printing
Daisy
Wheel High quality printing Slow, noisy, expensive
Thermal Light weight, battery
powered Slow, poor-quality
printing, requires
special
paper.
Plotter Prints colour and
graphics Expensive
Laser Excellent print
quality, prints graphics Expensive
Plotter:- Plotters
are output devices that are used to produce precise and good quality graphics
and drawings under computer control. They use ink pen or ink jet to draw graphics
or drawings. Either single colour or multicolor pens can be employed. The pens
are driven by a motor. The graphics and drawings produced by plotters are
uniform and precise and of very high quality. Plotters are used for complex
engineering drawings and for drawing of maps that require high degree of
accuracy. Flatbed plotters use horizontal flat surface on which paper can be
fixed. The pen moves in X and Y directions which is controlled by the computer.
They are mainly used for Computer Aided Design(CAD) and Computer Aided
Manufacturing(CAM) application such as printing out plans for houses or car
parts. These are also used with programs like AUTOCAD to give graphic outputs.
There are two different types of
plotters, one where the paper moves (drum), and the other where the paper is
stationary (flatbed plotter).
- Drum Plotters:- In drum plotters, the paper on which the design is to be made is
placed over a drum. These plotters consist of one or more pen(s) that are
mounted on a carriage and this carriage is horizontally placed across the
drum. The drum can rotate in either clockwise or anticlockwise direction
under the control of plotting instruction sent by the computer. In case, a
horizontal line is to be drawn, the horizontal movement of a pen is combined
with the vertical movement of a page via the drum. Moreover, plotters can
draw curves by creating a sequence of very short straight lines. In these
plotters, each pen can have ink of different colour to produce multicolor
designs. Drum plotters are used to produce continuous output, such as
plotting earthquake activity, or for long graphic output, such as tall
building structures.
- Flatbed Plotters:- Flatbed plotters consist
of a stationary horizontal plotting surface on which paper is fixed. The pen
is mounted on a carriage, which can move horizontally, vertically
leftwards or rightwards to draw lines. In flatbed plotters, the paper does
not move, the pen holding mechanism provides all the motion. These
plotters are instructed by the computer on the movement of pens in the X-Y
coordinates on the page. These plotters are capable of working on any standard,
that is , from A4 size paper to some very big beds. Depending on the size
of the flatbed surface, these are used in designing of ships, aircrafts,
buildings etc. The major disadvantages of this plotter is that it is a
slow output device and can take hours to complete a complex drawing.
3D
Printers:- 3D printing,
or additive manufacturing, is the construction of a three-dimensional
object from a CAD model or a digital 3D model.[1] The term "3D printing" can refer to a variety of
processes in which material is deposited, joined or solidified under computer control to create
a three-dimensional object,[2] with material being added together (such as liquid molecules
or powder grains being fused together), typically layer by layer.
In the 1980s, 3D printing techniques were considered
suitable only for the production of functional or aesthetic prototypes, and a more
appropriate term for it at the time was rapid
prototyping.[3] As of 2019, the precision, repeatability, and material range
of 3D printing have increased to the point that some 3D printing processes are
considered viable as an industrial-production technology, whereby the
term additive manufacturing can be used synonymously
with 3D printing. One of the key advantages of 3D printing is the
ability to produce very complex shapes or geometries that would be otherwise
impossible to construct by hand, including hollow parts or parts with internal
truss structures to reduce weight. Fused deposition modeling, or FDM,
is the most common 3D printing process in use as of 2020.[4]
Sound Card and Speakers:- An expansion
board that enables a computer to manipulate and output sounds. Sound cards are
necessary for nearly all CD-ROMs and have become common place on modern
personal computers. Sound cards enable the computer to output sound through
speakers connected to the board, to record sound input from a microphone
connected to the computer, and manipulate sound stored on a disk.
Nearly all sound cards MIDI, a standard for representing
music electronically. In addition, most sound cards are sound
Blaster-compatible, which means that they can process commands written for a
sound blaster card, the de facto standard for PC sound. Sound cards use two
basic methods to translate digital data into analog sounds.
- FM (Frequency Modulation) Synthesis mimics
different musical instruments according to built-in formulas.
- Wavetable Synthesis relies on recordings of
actual instruments to produce sound. Wavetable synthesis produces more
accurate sound, but is also more expensive.
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