Chapter – 3
PRINTER
A
computer peripheral that puts text or a computer generated image on paper or on
another medium, such as a transparency. Printer can be categorized in several
ways the most common distinction is IMPACT and NON-IMPACT.
IMPACT PRINTING
Is
the method used by the conventional type writers. In some type of impact
printing a metal “hammer” embossed with a character strikes a print ribbon,
which presses the characters image into paper. In other types the hammer
strikes the paper and presses it into the ribbon characters created through
impact printing can be formed by either a solid font or dot matrix printing
mechanism.
NON – IMPACT PRINTING
Does
not depend on the impact of metal on paper. In fact no physical contact at all
occurs between the printing mechanism and the paper. The most popular
non-impact methods today utilize thermal transfer, ink-jet.
TYPES OF
PRINTERS
1. DOT
MATRIX PRINTER
Any
printer that produces character made up of dots using a wire pin printed head.
The quality of output from a dot matrix printer depends largely on the number
of dots in the matrix, which might be low enough to show individual dots or
might be high enough to approach the look of fully formed characters. Dot
matrix printers are often categorized by the number of pins in the printer head
typically, 9 or 24.
2. LINE
PRINTERS
Any
printer that prints one line at one time, as opposed to one character at a time
or one page at a time. Line printer typically produce the 11 by 17 inch
“computer” printout. They are high speed devices and are often used with
mainframes, minicomputers, or networked machines rather than with single user
system. Types of line printers include chain printers and band printer.
3. LASER
PRINTERS
An
electrophotographic printer that is based on the technology used by
photocopiers. A focussed laser beam and a rotating mirror are used to draw an
image of the desired page on a photosensitive drum. This image is converted on
the drum into an electrostatic charge, which attracts and holds toner. A piece
of electrostatically charged paper is rolled against the drum, which pulls the
toner away from the drum and onto the paper. Heat is then applied to fuse the
toner to the paper. Finally, the electrified charge is removed from the drum and
the excess toner is collected. By omitting the final step and repeating only
the toner application and paper handling steps, the printer can make multiple
copies.
4. DAISY
WHEEL PRINTER
Daisy
wheel printer are some times called letter quality printer because they are
often used to produce attractive correspondence. The D.W.P is a flat circular
device made of metal with character embossed on it. As this wheel spins at a
very high speed the hammer hits the specific character against the ribbon which
presses against the paper.
5. THERMAL
TRANSFER PRINTER
It
is a kind of non-impact printer. In electrothermal printing, characters are
burned on to a special paper by heated rods on a print heat. They transfer ink
from a wax-based ribbon onto plain paper. These printer can support high
quality graphic.
6. INK –
JET PRINTER
It
is a kind of non-impact spray small dots of electrically charged ink onto a
paper to form images. Ink jet printer are flexible enough to be used as
plotters.
SECONDARY STORAGE DEVICES
Secondary
storage devices are also called backup storage because it is used to store
data. Volume of data on permanent basis which can be partially transferred to
the primary storage, when required for data processing. Afterwards these
devices are comparatively cheap and provide greater space to store the data
/instructions are stored on secondary storage devices in the same binary codes
as in primary storage.
NEEDS OF SECONDARY STORAGE DEVICE
The
storage capacity of the primary storage of today’s computer is not sufficient.
To store a large volume of data as a result additional memory called secondary
storage is needed with most of the computer system.
These devices also provides the fast communication than I/O devices. The
internal memory of a computer is a volatile memory. Therefore, we cannot save
the data permanently. In that case we require secondary storage device which
provide the facility to store the data for future use.
RANDOM ACCESS DEVICES
Random
Access Devices are those devices on which we can directly access the data.
These devices are comparatively provide the fast communication.
For example, hard disk, floppy disk, optical disk.
FLOPPY DISK
A
floppy disk, also called simply a diskette or disk, is a small flexible Mylar
disk coated with iron oxide on which data are stored. The floppy disk has been
around since early 1970s, today it is available in three 3½ inch, 5¼ inch and 8
inch sizes. The 5¼ and 8 inch diskettes are covered by stiff protective jacket
with different holes. The central big hole called hub ring which is used to
hold by disk drive during rotation. The elongated read write window is used to
read and write data through read/write head. The small hole next to the hub
ring is called index hole which is used to locating data through computer. The
cut out on the side of the floppy disk is called write protect notch. If we
cover this opening with a piece of paper then we can’t write data on to disk.
In small diskette a hard plastic cover and protective metal is used to protect
disk. Before using a disk we have to format a disk in which disk is divided
into tracks and sectors for storing the data. Diskettes may be double sided and
single sided while the storage capacity become less or more.
Floppy diskettes are more convenient to use with microcomputers. A floppy disk
which is a random access device can access data fast than magnetic tape.
SEQUENTIAL ACCESS DEVICES
Sequential
Access Devices are those in which we can access the data one by one in a
sequence. These devices provide slow communication as compared to Random Access
Device.
MAGNETIC TAPE
Magnetic
tape is a sequential access device about one half or one fourth inch in size
and made of Mylar (a plastic material) coated with a thin layer of iron oxide.
Data can be read and write through a device which is called tape drive. The
read/write head of tape drive which is an electromagnetic component read, write
and erase data from magnetic tape. Magnetic tape is divided into nine separate
strips or tracks in which eight tracks are used to store data and ninth track
is used for error checking bit.
Magnetic tape can store large quantities of data therefore they are erasable,
usable and durable secondary storage device. But it can use with large
computers.
INPUT DEVICES
Input
devices are used to provide data or information to the computer. The computer
follows the instructions given to it by and input device. A variety of input
devices are used with the computer depending on the type and purpose of input
information. For example, a keyboard is commonly used to transfer data or
information from human readable form to machine readable form. Other examples
of input devices are: mouse, joystick, trackball, light pens, digitizers,
scanners, optical character reader (OCR), touch window, etc.
MOUSE
The
mouse is an input device that usually contains one or two buttons. As a user
moves the mouse on a flat surface, the mouse controls the cursor movement on
the screen. When the user presses one of the buttons, the mouse either marks a
place on the screen or makes selection from data or menu on the screen. A mouse
has a sphere on its underside. This rotates as the mouse is moved along a flat
surface.
The mouse translate the direction and speed of rotation into a digital signals
that identifies the position or control, the cursor on the computer.
A mouse can be used for many application, ranging from games to drawing and
designing products with computer graphics. It provides an alternative for
people who are uncomfortable with a keyboard but it also can be used in
combination with a keyboard to input data.
TRACKBALL
A
Trackball is a pointing device almost like a mouse turned upside down. The user
controls the cursor on the screen by rolling a plastic ball with a fingertip or
wrist. To execute commands with a Trackball, one or more buttons are pressed,
much in the same way as is done with a mouse. The cursor can be moved around on
the screen by rolling the ball with a thumb or finger.
Trackball is popular among users of laptop computers when space is limited and
may be mounted on either side of the keyboard. For handicapped people who may
have difficulty pressing keys on a standard keyboard or using a mouse, the
trackball may be the answer since it edoes not require to moves the entire arm
to use it.
SCANNER
Scanner
is an input device. It is also called Optical Reader or Digital Scanner. It
scans or reads text and picture printed on a paper and enters them directly
into the computer memory.
The advantage of a scanner is that the user needs not type the input data in.
This is a lust and accurate method for entering data into the computer. The
scanner takes electronic images, of text or pictures from the paper it breaks
each image into light and dark dots and stores them into the computer memory in
machine codes. Scanned text can be edited by OCR software. Optical Character
Recognition (OCR) software translates the scanned document into text that can
be edited.
The image scanner is useful because it translates printed images into an
electronic format than can be stored in computer’s memory. The stored image can
be transferred into a paint program or directly into a word processor. You can
use software to organize and manipulate the electronic image.
KEYBOARD
A
keyboard is the most commonly used input device which helps us in simply keying
in required information in a computer. This information is subsequently stored
in the computer’s memory. A keyboard can be used effectively to communicate
with the computer but considered to be relatively slow as compared to other input
devices. The keyboard is divided into following divisions:
ALPHABETIC
KEYPAD
These keys are
similar to a standard typewriter and is used to type general information.
NUMBERIC
KEYPAD
These keys are used
to input numeric data only. These are very useful in case of large numeric data
input because all numeric keys can be accessed by one hand only. These keys can
also be used as an alternative to the screen navigation and editing keys.
FUNCTION
KEYS
These are keys
marked as F1 – F12, located normally at the top of the keyboard. These are
special keys provided to a programmer which allow him to attach special
functions to each key. Each of these function keys are also given some special
function in different packages.
SCREEN
NAVIGATION AND EDITING KEYS
These keys are
provided to move around in the screen. May programs use these keys to let the
user move around the screen display. In some keyboards these keys are also
provided inside the numeric keypad as alternate keys.
The description of commands assigned to function keys under the BASIC mode.
F1 – LIST Function – Used to display
the lines of your program on the screen.
F2 – RUN Function – Used to execute
a program from its beginning.
F3 – LOAD Function – Used to read a
program from a storage device and store it in main memory.
F4 – SAVE Function – Used to store a
program on a storage device from Memory.
F5 – COUNT Function – Used to
restart a program after it has temporarily interrupted by a stop or CTRL +
BREAK.
F6 – LPT1 Function – Used to
transfer data from the video screen to the line printer.
F7- TRON Function – Refers to “trace
on”. This function causes the line number of program line to be displayed as
these lines are executed.
F8 – TROFF Function – Refers to
“trace off”. This function cancels TRON function.
F9 – KEY Function – Use to change
the function of the other function keys.
F10 – SCREEN Function – Used to
return program to the character mode from the graphic mode and a;so to turn off
the colour.
OUTPUT DEVICES
An
output device is used to display the data or information that we receive from
the computer. An output device can be used to display or print the intermediate
or final results performed by computer. A variety of output devices are used
with computer. The use of these devices depends on the type and purpose of
output. Some examples of output devices are: Monitors, Printer, Plotters,
Visual display unit (VDU), liquid crystal display (LCD), etc.
MONITOR
To
display result or output from computer, a T.V like device is used which is
called monitor. The monitors are also referred as C.R.T (Cathode Ray Tube),
V.D.U (Visual Display Unit). The monitor assist during input from the keyboard,
this display is called a soft copy. The monitor can be of various kinds,
depending on the type of application. Monitors are categorized into two groups:
1. Monochrome monitors
2. Colour monitors
1.
MONOCHROME MONITORS
Monochrome monitors
are used specially for text editing purpose. These monitors can display only
one colour. Normally amber, green or paper white.
2. COLOUR
MONITORS
Colour monitors
serves a wide range of selection according to the application. Such as red,
green, blue, Enhance Graphic Array (EGA), Colour Graphic Array (CGA), Video
Graphics Array (VGA), Super Video Graphics Array (SVGA).
There are two types of colour monitors:
i. CRT Monitor
ii. LCD Monitor
i. CRT
MONITOR
The CRT monitors
are a lot like television set, using the same CRT or Cathorde Ray Tube
technology. The CRT monitor has two major parts; the screen and the cathode ray
tube (CRT). The screen is the front of the monitor and CRT is fitted inside the
monitor.
ii. LCD OR
FLAT PANEL MONITOR
Another monitor
type is LCD or Liquid Crystal Display. LCD monitors are a lot like CRT monitors
without the bulkiness but they do not have CRT. LCD monitors use a flat
lightweight surface filled with millions of tiny glass bubbles, each having a
phosphoric covering. These phosphoric coverings glow to create an image. LCD
screens provide clarity and flicker-free viewing.
PLOTTER
Plotter
is a special output device, which is used to produce high quality, perfectly
proportional hard copy output. Plotters are designed to produce large drawings
or images such as construction plans for buildings or blue prints for
mechanical devices. Plotters have been used in automotive and aircraft design,
topological surveys, architectural layouts and other similar complex drafting
jobs.
A plotter is composed of a pen, a move-able carriage, a drum and a holder for
chart paper. Both the pen and the paper can move up and down and back and
forth. This permits very detailed drawings. Some plotter having coloured pens
can make coloured drawings also.
There
are two types of plotters, which are as follows:
1. Drum Plotter
2. Flatbed Plotter
1. DRUM
PLOTTER
On the drum
plotter, the pens, and the drum move concurrently in different axes to produce
the image. Drum plotters are used to produce continuous output, such as
plotting earthquake activity, or for long graphic output, such as structural
view of a skyscraper.
2. FLATBED
PLOTTER
On some flatbed
plotters, the pen moves in both axes while the paper remains stationary.
However, on most desktop plotters, both paper and pen move concurrently in much
the same way as on drum plotters.
HARD DISK
Hard
disk is a thin circular metal plate coated both side with a magnetic material.
A hard disk pack consist of a number of disk mounted on central shaft which
rotate at a speed of 2400 rpm or more. In a hard disk information is stored on
both the surfaces of each disk plate except the upper and the lower surfaces of
the bottom plate which are not used. Information is recorded on the track of
the disk surfaces in the form of invisible tiny magnetic spot. The presence of
a magnetic spot represent 1 bit and its absence represents 0 bit.
Hard disk are potentially very high capacity storage devices typically in the
range of 20 megabyte to 1 gigabyte. Data are recorded on the tracks of a
spinning disk surface and read from the surface by one or more read/write
heads. There are two basic types of disk system.
1. Moving head
2. Fixed head
1. MOVING
HEAD
The
moving head consist of one read/write head for each disk surface mounted on an
axis and which can be moved in and out. In this system each read/write head
moves horizontally across the surface of the disk. So that it is able to access
each track individually. Information stored on the tracks which constitute a
cylindrical shape through the disk pack are therefore accessed simultaneously.
2. FIXED
HEAD
In
the fixed head system the axis are non-movable. A large number of read/write
heads are distributed over the disk surfaces. One head for each track as a
result no head movement is required and therefore information is accessed more
quickly.
VOICE RECOGNITION
A
voice recognition system compares a person’s live speech to their stored voice
pattern. Larger organizations sometimes use voice verification systems as time
attendance devices. Many companies also use this technology for access to
sensitive files and networks. Some financial services use voice verification
systems to secure telephone banking transactions. These systems use speaker
dependent voice recognition software. This type of software requires the
computer to make a profile of your voice, that is, you train the computer to
recognize your inflection patterns.
SHORT NOTES
DISK DRIVE
Disk
drive is a peripheral device that reads or write the disks (hard disks, floppy
disks, etc) that store information. Disk drives are called “Storage Device”
because they store information or portabel or permanent disks. The drive
contains a motor to rotate the disk at a constant rate and one or more
read/write heads, which are positioned over the desired track.
CD-WRITER
A
CD writer is a device connected to your computer which can write on CD-WR and
CD-R discs. CD-WR discs may be written, erased and rewritten, while CD-R discs
may be written only once. CD writer performances is measured in X unit, where
IX =150 kilobytes/sec. This allows user to master a CD-ROM or audio CD for
publishing CD-R devices can also read CD-ROMs and play audio CDs. The CD writer
is also called a CD-R drive (short for Compact Disc – Recordable Drive
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