chap 3 input and output devices

8/12/2019 Chap 3 Input and Output Devices

1/8

Input and Output Devices

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 IMPA! and "O"#IMPA!.

IMPACT PRINTING

Is the method used by the conventional type writers. In some type o$ impact printing a metal

%hammer& embossed with a character stri'es a print ribbon, which presses the characters image

into paper. In other types the hammer stri'es the paper and presses it into the ribbon characters

created through impact printing can be $ormed by either a solid $ont or dot matrix printingmechanism.

NON IMPACT PRINTING

Does not depend on the impact o$ metal on paper. In $act no physical contact at all occurs

between the printing mechanism and the paper. !he most popular non#impact methods todayutilize thermal trans$er, in'#(et.

TYPES OF PRINTERS

1. DOT MATRIX PRINTER

Any printer that produces character made up o$ dots using a wire pin printed head. !he )uality o$

output $rom a dot matrix printer depends largely on the number o$ dots in the matrix, whichmight be low enough to show individual dots or might be high enough to approach the loo' o$

$ully $ormed characters. Dot matrix printers are o$ten categorized by the number o$ pins in the

printer head typically, * or +.

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. -ine printer typically produce the by / inch %computer& printout. !hey are high speeddevices and are o$ten used with main$rames, minicomputers, or networ'ed machines rather than

with single user system. !ypes o$ line printers include chain printers and band printer.

3. LASER PRINTERS

An electrophotographic printer that is based on the technology used by photocopiers. A $ocussed

laser beam and a rotating mirror are used to draw an image o$ the desired page on a


2/8

photosensitive drum. !his image is converted on the drum into an electrostatic charge, which

attracts and holds toner. A piece o$ electrostatically charged paper is rolled against the drum,

which pulls the toner away $rom the drum and onto the paper. 0eat is then applied to $use thetoner to the paper. 1inally, the electri$ied charge is removed $rom the drum and the excess toner

is collected. 2y omitting the $inal step and repeating only the toner application and paper

handling steps, the printer can ma'e multiple copies.

4. DAISY WHEEL PRINTER

Daisy wheel printer are some times called letter )uality printer because they are o$ten used to

produce attractive correspondence. !he D.3.P is a $lat circular device made o$ metal with

character embossed on it. As this wheel spins at a very high speed the hammer hits the speci$iccharacter against the ribbon which presses against the paper.

5. THERMAL TRANSFER PRINTER

It is a 'ind o$ non#impact printer. In electrothermal printing, characters are burned on to a specialpaper by heated rods on a print heat. !hey trans$er in' $rom a wax#based ribbon onto plain paper.

!hese printer can support high )uality graphic.

6. INK JET PRINTER

It is a 'ind o$ non#impact spray small dots o$ electrically charged in' onto a paper to $orm

images. In' (et printer are $lexible enough to be used as plotters.

SECONDARY STORAGE DEVICES

4econdary storage devices are also called bac'up storage because it is used to store data. 5olumeo$ data on permanent basis which can be partially trans$erred to the primary storage, when

re)uired $or data processing. A$terwards these devices are comparatively cheap and provide

greater space to store the data 6instructions are stored on secondary storage devices in the same

binary codes as in primary storage.

NEEDS OF SECONDARY STORAGE DEVICE

!he storage capacity o$ the primary storage o$ today7s computer is not su$$icient. !o store a large

volume o$ data as a result additional memory called secondary storage is needed with most o$ the

computer system.

!hese devices also provides the $ast communication than I6O devices. !he internal memory o$ acomputer is a volatile memory. !here$ore, we cannot save the data permanently. In that case we

re)uire secondary storage device which provide the $acility to store the data $or $uture use.

RANDOM ACCESS DEVICES


3/8

8andom Access Devices are those devices on which we can directly access the data. !hese

devices are comparatively provide the $ast communication.

1or example, hard dis', $loppy dis', optical dis'.

FLOPPY DISK

A $loppy dis', also called simply a dis'ette or dis', is a small $lexible Mylar dis' coated with

iron oxide on which data are stored. !he $loppy dis' has been around since early */9s, today it

is available in three :; inch, inch sizes. !he inch dis'ettes are coveredby sti$$ protective (ac'et with di$$erent holes. !he central big hole called hub ring which is used

to hold by dis' drive during rotation. !he elongated read write window is used to read and write

data through read6write head. !he small hole next to the hub ring is called index hole which isused to locating data through computer. !he cut out on the side o$ the $loppy dis' is called write

protect notch. I$ we cover this opening with a piece o$ paper then we can7t write data on to dis'.

In small dis'ette a hard plastic cover and protective metal is used to protect dis'. 2e$ore using a

dis' we have to $ormat a dis' in which dis' is divided into trac's and sectors $or storing the data.

Dis'ettes may be double sided and single sided while the storage capacity become less or more.1loppy dis'ettes are more convenient to use with microcomputers. A $loppy dis' which is a

random access device can access data $ast than magnetic tape.

SEQUENTIAL ACCESS DEVICES

4e)uential Access Devices are those in which we can access the data one by one in a se)uence.

!hese devices provide slow communication as compared to 8andom Access Device.

MAGNETIC TAPE

Magnetic tape is a se)uential access device about one hal$ or one $ourth inch in size and made o$Mylar ?a plastic material@ coated with a thin layer o$ iron oxide. Data can be read and writethrough a device which is called tape drive. !he read6write head o$ tape drive which is an

electromagnetic component read, write and erase data $rom magnetic tape. Magnetic tape is

divided into nine separate strips or trac's in which eight trac's are used to store data and ninthtrac' is used $or error chec'ing bit.

Magnetic tape can store large )uantities o$ data there$ore they are erasable, usable and durable

secondary storage device. 2ut it can use with large computers.

INPUT DEVICES

Input devices are used to provide data or in$ormation to the computer. !he computer $ollows theinstructions given to it by and input device. A variety o$ input devices are used with the

computer depending on the type and purpose o$ input in$ormation. 1or example, a 'eyboard is

commonly used to trans$er data or in$ormation $rom human readable $orm to machine readable$orm. Other examples o$ input devices are mouse, (oystic', trac'ball, light pens, digitizers,

scanners, optical character reader ?O8@, touch window, etc.

MOUSE


4/8

!he mouse is an input device that usually contains one or two buttons. As a user moves the

mouse on a $lat sur$ace, the mouse controls the cursor movement on the screen. 3hen the user

presses one o$ the buttons, the mouse either mar's a place on the screen or ma'es selection $romdata or menu on the screen. A mouse has a sphere on its underside. !his rotates as the mouse is

moved along a $lat sur$ace.

!he mouse translate the direction and speed o$ rotation into a digital signals that identi$ies theposition or control, the cursor on the computer.

A mouse can be used $or many application, ranging $rom games to drawing and designing

products with computer graphics. It provides an alternative $or people who are uncom$ortablewith a 'eyboard but it also can be used in combination with a 'eyboard to input data.

TRACKBALL

A !rac'ball is a pointing device almost li'e a mouse turned upside down. !he user controls the

cursor on the screen by rolling a plastic ball with a $ingertip or wrist. !o execute commands with

a !rac'ball, one or more buttons are pressed, much in the same way as is done with a mouse.

!he cursor can be moved around on the screen by rolling the ball with a thumb or $inger.!rac'ball is popular among users o$ laptop computers when space is limited and may be

mounted on either side o$ the 'eyboard. 1or handicapped people who may have di$$icultypressing 'eys on a standard 'eyboard or using a mouse, the trac'ball may be the answer since it

edoes not re)uire to moves the entire arm to use it.

SCANNER

4canner is an input device. It is also called Optical 8eader or Digital 4canner. It scans or readstext and picture printed on a paper and enters them directly into the computer memory.

!he advantage o$ a scanner is that the user needs not type the input data in. !his is a lust and

accurate method $or entering data into the computer. !he scanner ta'es electronic images, o$ textor pictures $rom the paper it brea's each image into light and dar' dots and stores them into thecomputer memory in machine codes. 4canned text can be edited by O8 so$tware. Optical

haracter 8ecognition ?O8@ so$tware translates the scanned document into text that can be

edited.!he image scanner is use$ul because it translates printed images into an electronic $ormat than

can be stored in computer7s memory. !he stored image can be trans$erred into a paint program or

directly into a word processor. Bou can use so$tware to organize and manipulate the electronicimage.

KEYBOARD

A 'eyboard is the most commonly used input device which helps us in simply 'eying in re)uired

in$ormation in a computer. !his in$ormation is subse)uently stored in the computer7s memory. A

'eyboard can be used e$$ectively to communicate with the computer but considered to berelatively slow as compared to other input devices. !he 'eyboard is divided into $ollowing

divisions


5/8

ALPHABETIC KEYPAD

!hese 'eys are similar to a standard typewriter and is used to type general in$ormation.

NUMBERIC KEYPAD

!hese 'eys are used to input numeric data only. !hese are very use$ul in case o$ large numeric

data input because all numeric 'eys can be accessed by one hand only. !hese 'eys can also beused as an alternative to the screen navigation and editing 'eys.

FUNCTION KEYS

!hese are 'eys mar'ed as 1 C 1+, located normally at the top o$ the 'eyboard. !hese are

special 'eys provided to a programmer which allow him to attach special $unctions to each 'ey.

ach o$ these $unction 'eys are also given some special $unction in di$$erent pac'ages.

SCREEN NAI!ATION AND EDITIN! KEYS

!hese 'eys are provided to move around in the screen. May programs use these 'eys to let the

user move around the screen display. In some 'eyboards these 'eys are also provided inside the

numeric 'eypad as alternate 'eys.!he description o$ commands assigned to $unction 'eys under the 2A4I mode.

F1C -I4! 1unction C Esed to display the lines o$ your program on the screen.

F2C 8E" 1unction C Esed to execute a program $rom its beginning.F3C -OAD 1unction C Esed to read a program $rom a storage device and store it in mainmemory.

F4C 4A5 1unction C Esed to store a program on a storage device $rom Memory.F5C OE"! 1unction C Esed to restart a program a$ter it has temporarily interrupted by a stopor !8- F 28AG.

F6C -P! 1unction C Esed to trans$er data $rom the video screen to the line printer.

F7# !8O" 1unction C 8e$ers to %trace on&. !his $unction causes the line number o$ program lineto be displayed as these lines are executed.F8C !8O11 1unction C 8e$ers to %trace o$$&. !his $unction cancels !8O" $unction.FC GB 1unction C Ese to change the $unction o$ the other $unction 'eys.F1!C 48" 1unction C Esed to return program to the character mode $rom the graphic modeand aHso to turn o$$ the colour.

OUTPUT DEVICES

An output device is used to display the data or in$ormation that we receive $rom the computer.

An output device can be used to display or print the intermediate or $inal results per$ormed by

computer. A variety o$ output devices are used with computer. !he use o$ these devices dependson the type and purpose o$ output. 4ome examples o$ output devices are Monitors, Printer,

Plotters, 5isual display unit ?5DE@, li)uid crystal display ?-D@, etc.

MONITOR

!o display result or output $rom computer, a !.5 li'e device is used which is called monitor. !hemonitors are also re$erred as .8.! ?athode 8ay !ube@, 5.D.E ?5isual Display Enit@. !he


6/8

monitor assist during input $rom the 'eyboard, this display is called a so$t copy. !he monitor can

be o$ various 'inds, depending on the type o$ application. Monitors are categorized into two

groups. Monochrome monitors

+. olour monitors

1. MONOCHROME MONITORS

Monochrome monitors are used specially $or text editing purpose. !hese monitors can displayonly one colour. "ormally amber, green or paper white.

2. COLOUR MONITORS

olour monitors serves a wide range o$ selection according to the application. 4uch as red,green, blue, nhance raphic Array ?A@, olour raphic Array ?A@, 5ideo raphics

Array ?5A@, 4uper 5ideo raphics Array ?45A@.

!here are two types o$ colour monitors

i. 8! Monitor

ii. -D Monitor

". CRT MONITOR

!he 8! monitors are a lot li'e television set, using the same 8! or athorde 8ay !ube

technology. !he 8! monitor has two ma(or partsH the screen and the cathode ray tube ?8!@.!he screen is the $ront o$ the monitor and 8! is $itted inside the monitor.

"". LCD OR FLAT PANEL MONITOR

Another monitor type is -D or -i)uid rystal Display. -D monitors are a lot li'e 8!monitors without the bul'iness but they do not have 8!. -D monitors use a $lat lightweight

sur$ace $illed with millions o$ tiny glass bubbles, each having a phosphoric covering. !hese

phosphoric coverings glow to create an image. -D screens provide clarity and $lic'er#$reeviewing.

PLOTTER

Plotter is a special output device, which is used to produce high )uality, per$ectly proportional

hard copy output. Plotters are designed to produce large drawings or images such as construction

plans $or buildings or blue prints $or mechanical devices. Plotters have been used in automotiveand aircra$t design, topological surveys, architectural layouts and other similar complex dra$ting

(obs.

A plotter is composed o$ a pen, a move#able carriage, a drum and a holder $or chart paper. 2oth

the pen and the paper can move up and down and bac' and $orth. !his permits very detaileddrawings. 4ome plotter having coloured pens can ma'e coloured drawings also.

!here are two types o$ plotters, which are as $ollows

. Drum Plotter+. 1latbed Plotter


7/8


8/8

S"ORT NOTES

DISK DRIE

Dis' drive is a peripheral device that reads or write the dis's ?hard dis's, $loppy dis's, etc@ that

store in$ormation. Dis' drives are called %4torage Device& because they store in$ormation orportabel or permanent dis's. !he drive contains a motor to rotate the dis' at a constant rate and

one or more read6write heads, which are positioned over the desired trac'.

CD#WRITER

A D writer is a device connected to your computer which can write on D#38 and D#8discs. D#38 discs may be written, erased and rewritten, while D#8 discs may be written only

once. D writer per$ormances is measured in J unit, where IJ K

chap 3 input and output devices

Documents