1.0 Input Output Storage

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1.1 INPUT AND OUTPUT DEVICES

Mouse

• Used to control the movement of a pointer on the screen when it is moved horizontally over a

flat surface.

Uses:• Movement - controlling a screen pointer

• Can be used to draw objects in drawing and art packages.

Advantages:

• Usually supplied with a computer so no additional cost.

• All computer users tend to be familiar with using them.

Disadvantages:

• hey need a flat space close to the computer.

Tracker ball

• Used in the same way as a mouse but it is useful where desk space is limited.

• !t is like an upside down mouse because the user rotates the ball and the main body part stays

still.

Advantages:

• !deal for use where flat space close to the computer is limited.

• Can be useful with laptops as they can be built into the computer keyboard or clipped on.

Disadvantages:

• "ot supplied as standard so an additional cost and users have to learn how to use them.

Standard Keyboard

he standard #$%&' keyboard is the commonest way to enter text and numerical data into acomputer.

%ach individual key is a switch( which when pressed( sends a digital code to the computer.

Advantages:

• &eliable for data input of te)t and numbers.

• Usually supplied with a computer so no additional cost.

• *pecialised keyboards are available.

Disadvantages:

• Users may be slow for not very accurate typists.

• *low for accessing menus etc. and difficult to use if you want to move objects around the

screen.

• +ifficult for people unable to use keyboards through paralysis or muscular disorder.

Digital Camera

• hey are used to take photographs like a normal camera but produce digital images.

• he light passing through the lens is digitised by special light sensitive sensors. he image is

stored on memory chips in the camera and can then be transferred to a computer.

Advantages:

• "o film is needed and there are no film developing costs

• Unwanted images can be deleted straight away

• !mages are already digital and can easily be transferred to a computer and edited or transferred

over the !nternet

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• *pecial image editing software can allow a huge range of adjustments and special effects to be

tried

Disadvantages:

• !mages often have to be compressed to avoid using up too much e)pensive memory.

• hey are more e)pensive than the traditional cameras

Scanner • hese are used to digitise images of pages or objects.

• A light moves slowly over the surface of the picture or object to be scanned. he colours of the

reflected light are detected and digitised to build up a digital image. he digital data can then be saved by a computer as an image file.

• hey can be used with ,C& software to convert images of text into actual text data which can

be edited by a word processor.

Advantages:

• lat-bed scanners are very accurate and can produce images with a far higher resolution than a

digital camera

Disadvantages:

• Can produce very large image files which need a lot of computer memory to view and edit

Magnetic Strie !eader

• Magnetic stripes are thin strips of magnetic tape which are usually found on the back of plastic

credit and debit cards.

• $hen the card is inserted into a reader in an Automatic Teller Machine or ATM for example/

the tapes slides past a playback head similar to that used in a tape recorder. his reads the data

from the stripe and passes it to a computer.

Advantages:

• *imple to use and cheap to produce. he data can be altered if necessary.

Disadvantages:

• 0ery limited storage capacity. +ata easily destroyed by strong magnetic fields.

• "ot very secure as thieves can obtain the readers and alter the data.

"oystick

• 1oysticks are often used for playing computer games such as flight simulators. hey can also be

used to control the movement of a wheelchair or other machinery.

• hey input directional data like a mouse but work by switches being closed as the joystick is

moved left or right and up or down.

• Mini finger-controlled joysticks can be used to control a laptop cursor.

Advantages:

•

%asy to learn to use. 0ery simple design so they can be ine)pensive.Disadvantages:

• Control can be a bit crude as the directions in simple joysticks are limited to forward(

backwards( left and right. 2etter models offer diagonal movement or better.

Microhone

• his is used for the input of sound which is then digitised by the computer. he digital audio

can be saved for playback later on.

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• he digital audio can also be used with voice-recognition software to control hardware(

navigate a menu or input te)t into a word processor. 0oice recognition can also be used insecurity systems.

Advantages:

• 0oice recognition software can be used to convert your voice into te)t or to control menu

options on a phone system.

Disadvantages: • *tored audio files can take up a lot of memory.

• 0oice commands can be difficult to recognise by the software because of ascent.

#ideo digitiser

• A video digitiser is used to convert se3uences of analogue images into a digital format.

• he digitised images can then be saved as a file and played back on a monitor to produce a

moving image.

Advantages:

• +igital video is easily edited. *ections can easily be cut and pasted together and digital effects

added.

• he output can be rendered into a wide range of formats ranging from +0+ 3uality down tostreaming video suitable for the !nternet.

Disadvantages:

• 0ideo files take up a great deal of memory.

• ast video capture cards may be needed to capture high 3uality video footage.

• A powerful computer and graphics card is often needed to process video footage.

M$D$ instruments

• M!+! stands for Musical !nstrument +igital !nterface. hese are normal musical instruments

which have a M!+! port for input into a M!+! interface in the computer.

• he notes are converted into digital data and saved as a file on the computer. his data can be

converted back into notes or edited by computer software.

Advantages:

• +ata from a musical instrument is easily captured and edited with a computer.

• M!+! files are small.

• M!+! files can be recorded on one type of instrument and played back on another.

Disadvantages:

• Audio cannot be recorded directly as an audio file such as M45.

• he playback depends on the instrument6computer sound card so may not sound the same as

the original.

• ,nly the note and the timing are stored.

Sensors

• hese detect changes in the physical or chemical environment and convert them into electrical

signals. hese signals can then be digitised and used by the computer.

• *ensors are often used when data logging.

Advantages:

• here are a huge range of possible sensors and they include7 heat8 light8 sound8 movement8

magnetism8 pressure8 strain8 acidity p9/8 o)ygen levels8 li3uid levels8 humidity8 pulse rates8

salinity8 water flow8 speed and acceleration. *witch sensors can detect angles of tilt or whether

something is open or closed.

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Disadvantages:

• Most sensors need an interface to convert analogue signals into the digital signals that a

computer can understand.

!emote control

• hese emit a beam of infra-red light which carries digital data signals. hey are often used to

control 0:s and 0C&:s.• More advanced models can be programmed to transmit a series of commands with one button

press.

Advantages:

• %ach function can have its own button making them very simple to use.

Disadvantages:

• ,nly advanced models can be have the buttons reprogrammed so they cannot be used to

control anything other than the device they were designed for.

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%UT&UT D'#$C'S

&rinters:4rinters produce a printed :hard copy: on paper. +ifferent printers are suited to different purposes andhave a range of purchase and running costs.

4rinters can be divided up into three main types.

( ) Dot matrix rinters:

*o+ it +orks:

he print head travels from side to side across the paper and is made up of

numerous pins which are pushed out to form the shape of each character he pins hit an ink ribbon against the paper so the characters are printed out.

he paper is usually continuous with holes down each side and perforations so

the pages can be easily separated by tearing.2ecause the pins make an impact against the paper the characters can be printed

through several layers of self-carbonating paper to produce duplicate copies.

Uses:

• ;imited to situations where duplicate copies are needed and the 3uality is not too important.

• ypical uses might be in +arehouses where duplicate copies of orders need to produced

3uickly and cheaply.

Disadvantages7

• he printing ,uality is lo+ - these printers produce low to medium 3uality black and white

printing and can only print low resolution graphics.

• 2ecause of the impact of the pins against the paper( these printers can be ,uite noisy.

Advantages:

• he urchase cost is lo+ and the running costs are very lo+.

• hey can print fairly ,uickly( particularly if you remember that multiple copies are being printed in one print run.

• hey are robust and can operate in harsh environments.

• !f several sheets of self-carbonating paper are placed into the printer then the impact will

produce dulicate coies.

- ) $nk).et rinters:

*o+ it +orks:

• he print head contains tiny nozzles through which different coloured inks can be sprayed onto

the paper to form the characters or the graphic images.

• he ink is forced out by heat or by tiny piezoelectric crystals which change shape when an

electric current is applied across them.Suitable uses:

• A popular choice for home use where small amounts of printing are done and photographic

3uality colour printing is needed.

Disadvantages:

• he ink cartridges can be e)pensive so running costs can be high.

• he rinting seed is slo+ compared to a laser printer.

Advantages:

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• hese printers are relatively inexensive and produce high ,uality black and white or

photographic 3uality borderless colour printing.

/ ) 0aser rinters:

*o+ it +orks:

• hese print individual pages and work in a similar way to photocopiers.

•

A drum is charged to match the image and powdered ink toner/ sticks to the surface. hetoner is then transferred to the paper and fi)ed by heat and pressure.

• A school or business printer would have a typical speed of = pages per minute ppm/.

Suitable uses:

• Common wherever fast( high 3uality printing is re3uired.

Disadvantages7

• "on-colour laser printers are more exensive than ink).et rinters but the difference is

narrowing /.

• Colour laser printers are considerably more exensive. but their speed and high quality

output means they are becoming more popular /.

Advantages:

• hey are ,uiet and fast and produce high ,uality rintouts.• !unning cost are lo+ because although toner cartridges are e)pensive to replace( they last a

long time.

&lotters:*o+ it +orks:

• A drum lotter prints by moving a pen sideways over the surface of a sheet of paper.

• ,ne high precision motor moves the pen from side to side.

• Another high precision motor moves the paper backwards and forwards.

• An electromagnet lifts and drops different coloured ink pens onto the paper to draw lines.

• A flat)bed lotter uses two high precision motors( one to move the pen in the ? direction and

one to move it in the ' direction. he paper does not move.Suitable uses: 4lotters are restricted to line drawing and can only create a solid region of colour bydrawing a number of close( regular lines.

4lotters are often used in science and engineering applications for drawing building plans( printed

circuit boards and machine parts.

Advantages: hey are accurate and can produce far larger rintouts than standard printers.

Disadvantages:

• Slo+ and relatively exensive compared to printers.

• hey cannot print raster photographic/ images.

• hey can only fill solid blocks of colour using closely hatched lines.

'lectrical Transducers:An electrical transducer converts an electrical current into an output such as light( sound or movement.

Seakers:hese transducers convert an alternating electrical current into sound.

• Suitable uses ) hey can output music as well as the spoken word. Useful for blind users

where te)t or figures can be spoken by the computer. A speaker and computer-synthesised

voice can be used by automated systems to read information such as telephone numbers ortraffic updates.

• Advantages - Cheap and widely available. Capable of producing very high 3uality sound.

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• Disadvantages - they are an analogue device so the digital sound signal has to be converted(

usually by a sound card.

0ights:0ight 1ulbs7 hese use too much current to be powered directly by a computer but they can easily beswitched on using a relay which is an electronic switch. !n a relay a small current controls an

electromagnetic switch which can turn on or off the much larger current which powers the light bulb 2

• Suitable uses ) ;ight bulbs are used with relays and control systems in signalling( automaticlighting and burglar alarms.

Advantages - Chea and widely available.

Disadvantages - hey cannot be powered directly from a computer so need a relay to control them.

0ight)emitting diodes 30'D4s57 hese convert a small electrical current directly into light and can be

powered directly by a computer. oday:s ;%+s can be found in just about every colour of the spectrum

including invisible infra-red.

• Suitable uses ) ;%+:s are commonly used to indicate various events such as :power on: or :hard

disk in operation: and to monitor other control applications. !nfra-red ;%+:s are used to

transmit the data from a remote control to the receiver.

• Advantages - Chea( widely available and very reliable. ;%+:s use a tiny current so can be powered directly from a computer.

• Disadvantages - "one.

Motors:Motors are not usually powered directly from a computer as they use too much current. hey are

usually controlled through a relay which is an an electronic switch. !n a relay a small current controls

an electromagnetic switch which can turn on or off the much larger current which powers the motor.

• Suitable uses ) !n control technology( a computer can be programmed to turn motors on and off

using relay switches. %)amples include electronic doors and windows( cooling fans etc.

Motors are used in the automobile industry to move robot arms that spray body shells or

assemble and in electronics manufacturing to assemble delicate electronic components on a printed-circuit board.

• Advantages - Chea( widely available and very accurate.

• Disadvantages - hey cannot be powered directly from a computer so need a relay to control

them.

1u66ers:hese cheap transducers change a current directly into a simple sound. hey use a low current so can

be powered directly from a computer.

• Suitable uses ) ,ften used as alarms or warnings in computer control systems.

• Advantages - Chea and widely available. hey use a tiny current so can be powered directly

from a computer.

• Disadvantages - ;imited volume and they can only produce a limited range of sounds.

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Backing storage:The difference bet+een internal memory and backing storage:1acking storage also known as secondary storage/ means data storage that retains its contents whenthe computer is switched off. !t can be used to hold both programs and data.

$hen you run a program or load a file they are copied from the backing store into the internal

memory.

$hen you save a file it is copied from the internal memory to the backing store.• It is always slower to access data from backing storage than from primary

Memory.• Data stored in backing storage is permanent so it is NOT lost when the computer

is turned o.• Data stored in internal memory is lost when the computer is turned o.

Categories of storage media:1acking storage can be divided into three main categories:

• Magnetic media which stores the binary data on a disk or tape coated with amaterial that can be magnetised dierently, depending on whether a or ! is

stored.• Optical media which stores the binary data in a surface that re"ects laser light

dierently, depending on whether a or ! is stored.• Solid State Storage unit they lack mo#ing parts.

Magnetic media ) *ard discs:+ata is stored by magnetising the surface of flat( circular plates called latters which have a surface

that can be magnetised. hey constantly rotate at very high speed. A read6write head floats on acushion of air a fraction of a millimetre above the surface of the disc. he drive is inside a sealed unit

because even a speck of dust could cause the heads to crash.• Typical uses$

o The hard disc is usually the main backing storage media for a typicalcomputer or ser#er. It is used to store$ The operating system %e.g. Microsoft ® Windows& 'pplications software %e.g. word-processor, database, spreadsheet,

etc.& (iles such as documents, music, #ideo etc.

o ' typical home)school microcomputer would ha#e a disc capacity of o#er! gigabytes.

• Advantages$o *ery fast access to data. Data can be read directly from any part of the hard

disc %random access&. The access speed is about 1000 KB per second.o +a#e #ery large capacities

Magnetic media ) 7loy discs: These can be found on most microcomputers and accept the usual .- inch "oppy discs.+igh density discs for a / hold !.00 M1 of data %enough to store about 350 pages of A4text &. ' "oppy disc needs to be formatted before it can be used but most discs are nowsold already formatted for /2s.

• Typical uses$o (loppy discs are useful for transferring data between computers and for

keeping a back3up of small 4les.• Advantages

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o They are #ery cheap to buy and "oppy disc dri#es are #ery common.• !isadvantages$

o They ha#e very small storage capacity compared to modern alternati#essuch as 561 memory sticks.

o They are easily p"ysically damaged if unprotected and magnetic 4eldscan damage the data.

o They are relati#ely slow to access because "oppy discs rotate far moreslowly than hard discs, at only si7 re#olutions per second, and only startspinning when re8uested. The access speed is about #$ KB per second.

o Not all modern computers ha#e "oppy disk dri#es.

Magnetic media ) Magnetic Tae:1ust like the tape in a tape-recorder( the data is written to or read from the tape as it passes the magnetic

heads.• Typical uses$

o Magnetic tapes are often used to make a copy of hard discs for back3upreasons. The tapes are then kept in a safe place away from the ser#er.

• Advantageso Magnetic tape is relatively c"eap and tape cassettes can store very

large %uantities of data %typicay !" #$&.• !isadvantages$

o Accessing data is very slow and you cannot go directly to an item of dataon the tape as you can with a disc. It is necessary to start at the beginningof the tape and search for the data as the tape goes past the heads %serialaccess&.

%tical Media ) CD8D#D:hey are known as otical discs because the data is read6written by a laser beam reflecting or not

reflecting from the disc surface.

&!'(OM)!*! (OM 9 :OM means (ead Only Memory. This means you can only readfrom the disc, not write or store data onto it.

;ike a floppy disc( the disk only starts spinning when re3uested and it has to spin up to the correct

speed each time it is accessed. !t is much faster to access than a floy but it is currently slo+er than

a hard disc.• Typical uses

o Most software programs, music and 4lms are now sold on the disks• Advantages

o They are cheaper than the hard disko They are relati#ely tough as long as the surface does not get too scratched.

• !isadvantageso ;ou cannot sa#e 4les to a :OM disk.

&!'(s)!*! (s 9 : means (ecordable. These optical disks allow a user to write data on to the disc once, thereafter they become:OM.

• Typical useso +ome recording of music and 4lms.

• Advantageso Once burned data cannot be accidentally deleted.

• !isadvantages

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o They can be recorded only Once. In case of a mistake the disk is spoilt.

&!'(+s)!*! (+s 9 : means (e+ritable These optical disks allow a user to read and write data on to the disc se#eral times.

• !isadvantageso They are e7pensi#e compared to the /D)D*D :s.

Solid)State Storage Units The term

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1.0 Input Output Storage