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Hardware Work Book with practice

Questions

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3: H AR DW AR E HardwareMain hardware components of a general-purpose computerA computer is a programmable, electronic device. It receives input, stores and processes data, and produces output. Hardware means the physical parts of the computer. The main hardwarecomponents of a computer are: A Processor (CPU) Input Devices Main Memory Backing Storage Devices Output DevicesCPU: ''The CPU or Central Processing Unit is the brain of computer. It is the part which performs all the processing activities.''CPU receives data and instructions from input devices, processes them and gives output.In microprocessor CPU is housed in a small chip of silicon called microprocessor while in main frame and mini frame computer CPU is built in printed circuit board (pcb).F u n c ti o n s of CPU : Interprets the data and instructions. Generates control signals. Performs arithmetic & logical operations. Produces the address bits needed by memory.C omp o n e nts o f CPU :

Typical components of CPU are given below: Arithmetic & Logical UnitsMemory UnitRegisters

1. Arithmetic & Logical Unit (ALU):Arithmetic Unit performs all arithmetical operations like +, -, x, and ÷. Logical Unit performs comparison between two data pieces.ALU processed the data received from primary storage according to instruction received fromControl Unit.

2. Control Unit:CU is the main part of CPU which manages all the resources of CPU. It is like a traffic cop directing flow of data.The functions of CU are given below:Interprets and carries out instruction of program. Selects program statements from memory.Moves these instructions to instruction registersCarries out instructionsDirects flow of data between components of CPU and to and from other devices.

3. Registers:

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Registers are high speed volatile or temporary memory built in CPU.Data currently being processed is stored in registers. There are 14 basic registers

shared by ALU and CU.

Computers and processing powerComputers vary in power. In descending order of processor power, they are:

supercomputer mainframe PC or laptop Netbook, palmtop or PDA.

A computer is often embedded into an appliance in the form of a microcontroller, which combines the processor with memory, backing storage and other circuitry in a single integrated circuit.I n p ut D e v i c e s: Input devices allow us to enter raw data into a computer. The computer processes the data and then produces outputs that we can understand using an output device. Input devices can be manual or automatic.There are two different categories of input device. They are:M a n u a l I n p u t D e v i c e s : With a manual input device the user must enter data into the computerby hand. e.g. m o u s e , keyboard, sca n n e r .D i rect D ata E n t ry ( DDE ) D e v i c e s : A direct data entry device can transfer information automatically from a source document such as a form or barcode into the computer. The user does not need to manually enter the information. e.g. o p t i cal m a r k r e c o g n i t i o n , s m a r t card s .There are many different input devices available. Each input device is suitable for a differentpurpose. Below you will find descriptions of the most common manual input and direct data entry devices.Mouse

The mouse is used to control the movement of a pointer on the screen when it is moved horizontally over a flat surface.A ball under the mouse rotates when it is moved and turns two rods, one forleft/right and one for up/down.Buttons on the mouse let you select options from menus and drag objects around the screen etc. Some models are now wireless.

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Uses: Movement - controlling a screen pointer Buttons - selecting items / menus etc.

Advantages: Ideal for use with desktop computers. Usually supplied with a computer so no additional cost. All computer users tend to be familiar with using them.

Disadvantages: They need a flat space close to the computer. The mouse cannot easily be used with laptop, notebook or palmtop computers.

(These need a tracker ball or a touch sensitive pad called a touch pad).Tracker ball

A tracker ball is used in the same way as a mouse but it is useful where desk space is limited.It is like an upside down mouse because the user rotates the ball and themain body part stays still. It has buttons like a standard mouse.

Advantages: Ideal 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:

Not supplied as standard so an additional cost and users have to learn how to use them.

Standard Keyboard (F u r th e r k e ybo a r d s t yp e s ) The standard QWERTY keyboard is the commonest way to enter text andnumerical data into a computer.Each individual key is a switch, which when pressed, sends a digital code to the computer.For example, pressing the 'A' key produces the binary

code 01100001representing the lower case letter 'a'. Holding down the shift key at the same time produces the binary code01000001 representing the upper case letter 'A'.Advantages:

Reliable for data input of text and numbers. Usually supplied with a computer so no additional cost. Specialised keyboards are available.

Disadvantages: Users may be slow for not very accurate typists.

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Slow for accessing menus etc. and difficult to use if you want to move objects around the screen.

Difficult for people unable to use keyboards through paralysis or muscular disorder.Digital camera

These are used to take photographs like a normal camera but produce digital images instead of using film.The light passing through the lens is digitised by special light sensitivesensors. The image is stored on memory chips in the camera and can

then be transferred to a computer.The resolution of such cameras is increasing rapidly and professional models have become standard in photo-journalism. Images are usually compressed as jpeg's to save memory. Advanced models have removable memory cards to increase the camera's storage capacity. Images can be transferred to a computer by cables or memory cardreaders.Advantages:

No film is needed and there are no film developing costs Unwanted images can be deleted straight away Images are already digital and can easily be transferred to a computer and edited or

transferred over the Internet Special image editing software can allow a huge range of adjustments and

special effects to be triedDisadvantages:

Images often have to be compressed to avoid using up too much expensive memory.Scanner

These are used to digitise images of pages or objects.A light moves slowly over the surface of the picture or object to be scanned. The colours of the reflected light are detected and digitised to build up a digital image. The digital data can then be saved by a computer as an image file.

They can be used with OCR s oftware to convert images of text into actual text data whichcan be edited by a word processor.Advantages:

Flat-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 editMagnetic Stripe Reader

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Advantages:

Magnetic stripes are thin strips of magnetic tape which are usually found on the back of plastic credit and debit cards.When the card is inserted into a reader (in an Automatic Teller Machineor ATM for example) the tapes slides past a playback head similar to that used in a tape recorder. This reads the data from the stripe and passes it to a computer.

Simple to use and cheap to produce. The data can be altered if necessary.Disadvantages:

Very limited storage capacity. Data easily destroyed by strong magnetic fields. Not very secure as thieves can obtain the readers and alter the data.

JoystickJoysticks are often used for playing computer games such as flight simulators. They can also be used to control the movement of a wheelchair or other machinery.They input directional data like a mouse but workby 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:

Easy to learn to use. Very simple design so they can be inexpensive.Disadvantages:

Control can be a bit crude as the directions in simple joysticks are limited to forward, backwards, left and right. Better models offer diagonal movement or better.

MicrophoneThis is used for the input of sound which is then digitised by the computer. The digital audio can be saved for playback later on.The digital audio can also be used with voice-recognition software to control hardware, navigate a menu or input text into a word processor. Voice

recognition can also be used in security systems.Advantages:

Voice recognition software can be used to convert your voice into text or to control menu options on a phone system.

Disadvantages: Stored audio files can take up a lot of memory.

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Voice commands can be difficult to recognise by the software.

Video digitiser

A video digitiser is used to convert sequences of a n a l o gu e i mages into a d i g i t a l f ormat.The digitised images can then be saved as a file and played back ona monitor to produce a moving image.Software will allow the video to be edited and special effects added, as well as individual still images to be captured and saved. Digital

video cameras digitise the image inside the camera and save the video frames in a digital format. This data can then be transferred directly to the computer via a fast transfer cable and interface such as Firewire.Advantages:

Digital video is easily edited. Sections can easily be cut and pasted together and digital effects added.

The output can be rendered into a wide range of formats ranging from DVD qualitydown to streaming video suitable for the Internet.

Disadvantages: Video files take up a great deal of memory. Fast video capture cards may be needed to capture high quality video footage. A powerful computer and graphics card is often needed to process video footage.

MIDI instruments

MIDI stands for Musical Instrument Digital Interface. These are normal musical instruments which have a MIDI port for input into a MIDI interface in the computer.The notes are converted into digital data and saved as a file on the

computer. This data can be converted back into notes or edited by computer software. The software often has a wide range of special effects or stored sound data from realinstruments.Advantages:

Data from a musical instrument is easily captured and edited with a computer. MIDI files are small. MIDI files can be recorded on one type of instrument and played back on another.

Disadvantages: Audio cannot be recorded directly as an audio files such as MP3. The playback depends on the instrument/computer sound card so may not sound the

same as the original. Only the note and the timing are stored.

SensorsThese detect changes in the physical or chemical environment and convert them into electrical signals. These signals can then be digitised and used by the computer.Sensors are often used when d ata l ogg ing .

Advantages: There are a huge range of possible sensors and they include: heat; light; sound;

movement; magnetism; pressure; strain; acidity (pH); oxygen levels; liquid levels; humidity; pulse rates; salinity; water flow; speed and acceleration. Switch sensors can detect angles of tilt or whether something is open or closed.

Disadvantages: Most sensors need an interface to convert analogue signals into the digital signals

that a computer can understand.

Remote controlThese emit a beam of infra-red light which carries digital data signals. They are often used to control TV's and VCR's.More advanced models can be programmed to transmit a series of commands with onebutton press.

Advantages:1. Each function can have its own button making them very simple to use.

Disadvantages: Only advanced models can be have the buttons reprogrammed so they cannot

be used to control anything other than the device they were designed for.

Concept KeyboardA concept keyboard is a flat board which contains a grid of switches. Each switch can be programmed to do whatever you want. An overlay image is placed on top of the grid so that the

user can tell what pressing on different areas (switches) will do. Example uses of concept keyboards include :

Games for young children : The overlay image could be a picture of a farmyard.Pressing on an animal would cause the computer to make the noise the animal does.

Tills in restaurants/pubs : The overlay contains a list of all the meals that can be sold.Instead of typing in prices the waiter simply presses the keyboard where the meals/drinks he is serving are listed.

Concept keyboards are particularly useful for people who would find using an ordinary keyboard difficult and in locations where an ordinary keyboard might be damaged, e.g. by spillage or dust.Touch Sensitive ScreensThese screens do a similar job to concept keyboards. A grid of light beams or fine wires criss- cross the computer screen. When you touch the screen the computer senses where you have pressed. Touch screens can be used to choose options which are displayed on the screen. Touch screens are not used very often as they are not very accurate, tiring to use for a long period and are more expensive than alternatives like a mouse. The main applications for which touch screens are used is the provision of public information systems. Touch screen operated computers can be found in places such as travel agents and airports.

Light PenA light pen is a special pen which you can point at any computer monitor. When the pen is pointed at the screen the computer can work out where the pen is pointing. Light pens can be used to "draw" on the screen or to select options from menus presented on the screen. Light pens are extremely poor input devices. They are very inaccurate and tiring to use. Light pens are hardly ever used today.

Graphics TabletGraphics tablets are used mainly by professionalgraphics designers. Using a graphics tablet a designer can produce much more accurate drawings on the screen than he could with a mouse or other pointing device. A graphics tabletconsists of a flat pad (the tablet) on which the user "draws" with a special pen called a stylus.As the user "draws" on the pad the image is created on the screen. The pad on which the user draws can be any size from A5 to A1 (eight times as large as an A4 page). Drawings created using a graphics tablet can be accurate to withing hundredths of an inch.The stylus that the user draws with may have a button on it which will act like a mouse button. Sometimes instead of a stylus a highly accurate mouse-like device called a puck is used todraw on the tablet.ScannerDirect Data Entry Devices

Direct data entry devices are used when large volumes of data must be entered into the computer quickly. Consider how long it would take for the cashier to add up the cost of your shopping if she had to enter the price of every item you purchased. Nowadays barcode systems make this task much quicker. There are a variety of different direct data entry devices available. Different devices are suitable for different applications (tasks).Bar Code ReadersBar codes are often printed on products that we buy and are used by shops to produce bills for customers. A bar code is made up of a sequenceof bars of different widths. Different groups of bars are used to represent different numbers. A printed bar code is therefore simply a way of representinga number. The number is often printed above or below the bar code so that humans can read it.Bar codes are read into the computer using a wand or a fixed scanner. Bar codes are not easilydamaged and can normally still be read if they are creased or not stuck onto a flat surface. Theycan be printed using a normal printer and ink and so are cheap to produce. The information normally included on a bar code for a product is country of origin, manufacturer and item code. The price is not included in the bar code.

A scanner can read a barcode number incorrectly. A ch e c k d i g i t i s inluded in the barcode number to reduce the likelihood of this happening.Magnetic Stripe CodesMagnetic stripes are built into many plastic cards such as cheque guarantee or credit cards. Magnetic stripes look like this :

The strip can contain up to 60 characters (numbers or digits) of information which is stored magnetically. Usually the information is put onto the stripe when the card is made and is never changed. Magnetic stripe codes can also sometimes be found on the back of railway tickets.To be read the card is swiped through a machine which quickly and accurately reads the pattern of magnetism. The information stored on the card can be destroyed by exposure to magnetic fields, by scratching or by coming into contact with some liquids.Smart CardsSmart cards are often called input devices. In fact they are actually simple s t ora g e d e v i ce s . A smart card contains a small R A M ch ip. When the card is put into a machine data can be read from the card or written onto it. A smart card can store much more data than a magnetic stripe can. A popular card in use at the moment can store 8k (about 8000 characters) of information.Petrol companies and supermarkets use smart cards to store information about points that customers earn when they buy goods. Every time the customer buys something the number of points stored on the card is increased. The

customer can then spend these points to buy goods.Satellite television companies also use smart cards in their receivers. The smart card stores a code which is needed to let the receiver decode and display the pictures coming from the satellite. The government is currently considering introducing an identity card which could be based on a smart card. Many people are worried about this as people would not be able to tell what information was stored about them.A new generation of smart cards is now appearing which contain a small m i c r o p r o cess o r a s well as memory. These cards are practically a complete computer system on a card.Magnetic Ink Character Recognition (MICR)The MICR system reads characters printed in a special magnetic ink into the computer. The main users of MICR are banks. They use it to read information from cheques into their computers so that the cheques can be cashed. Here is some information stored on a cheque using MICR :

The information printed on the cheque using MICR is : A unique number for the cheque. A code that identifies the bank and branch that issued the cheque. The number of the account that the cheque relates to.

MICR readers can only read one special font which can represent only numbers and a few punctuation marks. They can read characters very quickly and with 100% accuracy. Information printed in magnetic ink is also very secure. It is not possible to change the information by writing over it with a pen and the printed numbers are not damaged by folding (as often happens with cheques). Both the reader used by MICR and the special ink are expensive.Optical Character Recognition (OCR)An optical character recognition system consists of a sca n n e r a nd some software. The scanner is used to scan an image of a page of text to be read into the computer. The software then examines the page and extracts the text from it, storing it in a form that can be processed.OCR systems can now recognise a wide variety of computer fonts and read letters with over95% accuracy. Some systems will recognise hand-written text reasonably well as long as it is written very neatly and usually put into boxes on a pre-printed form.Optical Mark Recognition (OMR)An optical mark reader reads marks made by pencil on a printed form into the computer. OMR systems are used by examination boards to collect the answers to multiple choice examinations and to purchase lottery tickets. Here is an example answer grid for an examination :

The student answers each question by drawing a line in pencil in the box that he/she thinks is the correct one. The answer grid is printed in a special coloured ink called that the OMR system will ignore. Marks down the side of the form are used to automatically line the form up in the

reader so that it can be read. The reader detects where the marks are placed by shining a light at the page and measuring the amount of light reflected. Less light is reflected where the marks have been made. A pile of forms collected at the end of an examination can be put into a tray (called a bin). The reader will go through each form in turn and record the candidates marks. Input using OMR is accurate and very fast. Problems can occur if the OMR forms get creased as the reader may jam.Turnaround DocumentsO ptic a l m a r k r e c o g n i t i on and o p t i cal ch a r act e r r ec o g n i t i on are often used together in a turnaround document. A turnaround document is a document which :

Has some information printed onto it by a computer. Has more information added to it by a human. Is fed back into a computer to transfer the added information into the computer.

Here is a turnaround document that a gas company could use to record meter readings.

The document is printed by a computer. The name, address and customer number of the person that the meter reader should visit is printed on the form. The customer's last meter reading is also included.The meter reader takes the document and visits the customer's house. He then marks the current meter reading onto the OMR grid on the form. In the example the meter reader hasmarked the reading as 4605. The form is then returned to the gas company.At the gas company the form is fed into a special reader. Optical character recognition is used to read the customer's number from the form. Optical mark recognition is used to read the meterreading that has been added. All of the information can be read into the computer automatically.A bill can be produced and posted to the customer without any need for human intervention. Turnaround documents allow cheap, fast input of information into a computer systemThe turnaround document does not contain any instructions because the meter reader who fillsit in will complete hundreds of similar forms every day. He will have been trained to use the forms so printing instructions on them would simply waste space.SensorsS e n sors can be used to measure physical quantities such as temperature, light and pressure. The measurements can then be stored for later use (d a t a l o g g i ng ) or used to control devices such as heaters or fans (compu t e r co nt r o l ). common sensors include:

– microswitch– Reed switch– Temperature sensor– Pressure sensor– Light sensor

– Infrared (IR) sensor– Distance sensor– Speed sensor– Humidity sensor– Moisture sensor– Gas sensor.

Most sensors produce analogue signals that need to be digitised or converted into digital data by an analogue-to-digital converter (ADC).

Output devicesAs with input devices, you need to be able to select devices that are suitable for a particular computer application.The different types of devices are, how they work and what they are used for:• monitor, e.g. a CRT or LCD screen• multimedia projector• printer or plotter, e.g. laser, inkjet and dot matrix• loudspeakers and headphones• actuators make physical changes; they include:

– light bulb or LED– heater– heat-pump– solenoid– relay or contactor– motor

– pump– buzzer and similar actuators such as bell, beeper or siren.

Many output devices require analogue signals, so the computer‘s digital output needs to beconverted by a digital-to-analogue converter (DAC).

―A monitor is an output device used to display on a screen, text and graphics (soft copy)generated by CPU.‖

It is also called Video Display Unit. It is the most popular output device. The picture elements or dots which display images and text on screen are called pixels.

Screen Size:The screen size of monitor is measured in diagonal inches i.e. the distance from one

corner to other diagonal corner. A typical size of monitor is 14 inches. A monitor that is 16 ormore inches diagonally is called full-page monitors. A monitor may be portrait (height greaterthan width) or landscape (width greater than height).

Monitors:The computer monitor (also know as a VDU or Visual Display Unit) is the most common computer output device. For desktop computers, cathode ray monitors (CRT) are gradually being replaced by flat-screen monitors such as the Liquid Crystal Displays (LCD) and ThinFilm Transistor (TFT) displays used with laptop computers because they use less power and take up less space. [ F u r t h e r i n f o r ma t i on on moni t o rs ]Suitable uses - displaying text, images and numbers in full colour. Advantages - relatively cheap and reliable, can displaytext and graphics in a wide range of colours. They are also quiet and do not waste paper.Disadvantages - no permanent copy to keep and unsuitable for users with visual problems.

P r i nt e rs: Printers produce a printed 'hard copy' on paper. Different printers are suited to different purposes and have a range of purchase and running costs. [ F u r t h e r n o t e s on C o l o u r pr i n t i n g ]Printers can be divided up into three main types.1 - Dot matrix printers:How it works: The 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 characterThe pins hit an ink ribbon against the paper so the characters are printed out. The paper is usually continuous with holes down each side and perforations sothe pages can be easily separated by tearing.

Because the pins make an impact against the paper the characters can be printed through several layers of self-carbonating paper to produce duplicate

copies.An animation showing how head of a 21 pin dot-matrix printer movesacross the paper, firing the pins that strike the ink against the paper.

Suitable uses: Limited to situations where duplicate copies are needed and the quality is not too important.Typical uses might be in warehouses where duplicate copies of orders need to produced quickly and cheaply.

Disadvantages: The printing quality is low - these printers produce low to medium quality black and white printing and can only print low resolution graphics.Because of the impact of the pins against the paper, these printers can be quite noisy.

Advantages: The purchase cost is low and the running costs are very low.They can print fairly quickly, particularly if you remember that multiple copies are being printed in one print run.They are robust and can operate in harsh environments.If several sheets of self-carbonating paper are placed into the printer then the impact will produce duplicate copies.

2 - Ink-jet printers:

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How it works: The print head contains tiny nozzles through which different coloured inks can be sprayed onto the paper to form the characters or the graphic images. The 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 quality colour printing is needed.

Disadvantages: The ink cartridges can be expensive so running costs can be high.The printing speed is slow compared to a laser printer.

Advantages: These printers are relatively inexpensive and produce high quality black and white or photographic quality borderless colour printing.

3 - Laser printers:How it works: These 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. The toner is then transferred to the paper and fixed by heat andpressure.A school or business printer would have a typical speed of 10 to 20 pages per minute (ppm).

Suitable uses: Common wherever fast, high quality printing is required.Disadvantages: Non-colour laser printers are more expensive than ink-jet printers (but the

difference is narrowing).Colour laser printers are considerably more expensive. (but their speed and high quality output means they are becoming more popular).

Advantages: They are quiet and fast and produce high quality printouts.Running cost are low because although toner cartridges are expensive to replace, they last a long time.

Plotters:

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How it works: A drum plotter print s by moving a pen sideways over the surface of a sheet of paper.One high precisionmotormoves thepen from side to side.Another high precision motor moves the paper backwards and forwards.An electromagnet lifts and drops different coloured inkpens onto the paper to draw lines.A flat-bed plotter uses two high precision motors, one to move the pen in the X direction and on it in the Y direction. The paper does not move.

Suitable uses: Plotters are restricted to line drawing and can only create a solid region of colour by drawing a number of close, regular lines. Plotters are often used in science and engineering applications for drawing building plans, printed circuit boards and machine parts.

Advantages: They are accurate and can produce far larger printouts than standard printers.

Disadvantages: Slow and relatively expensive compared to printers.They cannot print raster (photographic) images.They can only fill solid blocks of colour using closely hatched lines.

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Braille printer - by converting text into the Braille code, this printer produces patterns of raised dots on paper for use by the blind.

Electrical Transducers:A electrical transducer converts an electrical current into an output such as light,

sound or movement.Speakers:These transducers convert an alternating electrical current into sound.Suitable uses - They can output music as well as the spoken word. Useful for blind users where text or figures can be spoken by the computer. A speaker and computer-synthesised voice canbe used by automated systems to read information such as telephone numbers or trafficupdates.Advantages - Cheap and widely available. Capable of producing very high quality sound. Disadvantages - they are an analogue device so the digital sound signal has to be converted,usually by a sound card.Lights:Light Bulbs: These use too much current to be powered directly by a computer but they can easily be switched on using a relay which is an an electronic switch. In a relay a small current controls an electromagnetic switch which can turn on or off the much larger current which powers the light bulb.Suitable uses - Light bulbs are used with relays and control systems in signalling, automaticlighting and burglar alarms.Advantages - Cheap and widely available.Disadvantages - They cannot be powered directly from a computer so need a relay to control them.Light-emitting diodes (LED's): These convert a small electrical current directly into light and canbe powered directly by a computer. Today's LEDs can be found in just about every colour of thespectrum including invisible infra-red.Suitable uses - LED's are commonly used to indicate various events such as 'power on' or 'harddisk in operation' and to monitor other control applications. Infra-red LED's are used to transmit the data from a remote control to the receiver.Advantages - Cheap, widely available and very reliable. LED's use a tiny current so can be powered directly from a computer.Disadvantages - None. Motors:Motors are not usually powered directly from a computer as they use too much current. They are usually controlled through a relay which is an an electronic switch. In a relay a small current controls an electromagnetic switch which can turn on oroff the much larger current which powers the motor. Suitable uses - In control technology, a computer canbe programmed to turn motors on and off using relay switches. Examples include electronic doors and windows, cooling fans etc. Motors are used in theautomobile industry to move robot arms that spray body shells or assemble and in electronics manufacturing toassemble delicate electronic components on a printed- circuit board.

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Advantages - Cheap, widely available and very accurate.Disadvantages - They cannot be powered directly from a computer so need a relay to control them.Buzzers:These cheap transducers change a current directly into a simple sound. They use a low current so can be powered directly from a computer.Suitable uses - Often used as alarms or warnings in computer control systems.Advantages - Cheap and widely available. They use a tiny current so can be powered directly from a computer.Disadvantages - Limited volume and they can only produce a limited range of sounds.

A normal PC has no way of affecting what is happening around it. It can‘t turn on the lights, ormake the room hotter. How do we change what is happening around us? We useour muscles to move things, press things, lift things, etc. (and we can also make sound using our voice).

A normal PC has no muscles, but we can give it some. In fact we can give it the ability to do lots of things by connecting a range of actuators to it…

An actuator is a device, controlled by a computer, that can affect the real-world.

Examples of actuators, and what they can do are...Actuator What it Can Do

Light bulb or LED Creates light

Heater Increases temperature

Cooling Unit Decreases temperature

Motor Spins things around

Pump Pushes water / air through pipes

Buzzer / Bell / Siren Creates noise

Actuators are used extensively in compu t er co n tr o l s y s t ems .

Note: some of these devices require an analogue signal to operate them. This means that they need to be connected to the computer using ad i g i t a l -t o - a n a l o g ue co n v e rt o r ( DAC)MotorMotors can provide movement.

For example, the motor in a washing machine can be controlled by a computer - it is switched on when the clothes are loaded for washing andswitched off at the end of the wash.

Computer-controlled motors are also found

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in microwave ovens (to turn the food around) and air-conditioning units (to drive the fan)

PumpsA pump is basically a motor attached to a device that can push water or air along pipes. When the motor isswitched on, water or air flows along the pipes toplaces it is needed.

Pumps are used in many places: as part of watering systems in greenhouses, in factories, etc.

BuzzerBuzzers can provide noise.

For example, the buzzer in a microwave oven can be switched on by the controlling computer when the food is cooked.

Louder noises can be made using a siren or an electric bell, for example in a burglar alarm system.

LightsLightbulbs and LEDs can by used to provide light, or to indicatesomething.

For example, computer-controlled lights are used in trafficlights, at music concerts. Lights are used in car dashboards to show if the any of the systems in the car have problems.

Heaters / CoolersHeaters can provide heat, and coolers can cool things down.

A computer can switch a heater on or off when needed to keep a room or agreenhouse at the correct temperature during winter.

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A computer can switch a cooling unit on or off to keep a room at the correct temperature during hot weather, or to keep food fresh.

D u a l P urpose D e v i ces: ―A device which is used as an input device as well as out device is called Dual Purpose

Device or I/O Device.‖

These devices perform following two tasks:Writing Data: Writing data or recording data on the surface of a disk or

tapes, where it is stored for later use.Reading Data: Reading or retrieving the data from the surface of a disk or tape,

then transferring it into the computer‘s memory.

Following are the most common I/O devices: Disk DriveCD Writer

Disk Drive:Disk drives read and write data and information on disks like hard disks and also called storage devices.Disk drives have a motor to rotate the disk and read/write heads, which are positioned over desired track.As an input device, disk drive reads data from disk while as output device disk drive write data on disk.The redial motion of head is called ―Seeking‖. The set of locations which are accessible with theheads in a given radial position is called ―Cylinder‖. The Seek Time‖ is the time taken to seek a different cylinder. The disk is continuously rotating and the heads move backward and forward until desired location is found.

CD Writer:CD Writer is a dual purpose device used to write data and information on CD-R and CD RWdiscs and read data and information from them.

CD-R discs are once writable while CD-RW discs are rewritable and erasable.The speed of CD Writer is measured in ―X‖ where 1X equals 150 KiloBytes/Second.CD Writers are also called CD-R drive or Compact Disk Recordable Drive

Understanding the Differences between LED, LCD and DLP Projectors

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Ideal for delivering lectures and presentations to large groups, as well as watching movies and other videos, projectors can be found in a variety of environments, including classrooms, conference rooms, and even home theaters. Projectors range in size and capabilities,from h a n d h el d de v i ces t hat need a dark room to deliver a viewable image to h i g h - p o w ered d e v i ces t hat are easily read, even in brightly lit offices. Projectors can be purchased fromelectronics retailers or specialty stores dealing in camera and projection equipment. For consumers who prefer to shop online, sites like eBay are excellent options. This buying guidewill discuss the differences between three kinds of projectors: LED, LCD, and DLP projectors. It will also explain how the technology works, and weigh the advantages of each for consumers. DLP, LCD, and LED TechnologyThe technology used in projectors can generally be broken down into two types: transmissive or reflective. Because LCD projectors pass light through the LCD panels rather than bouncing itaway, they are considered a transmissive medium. A DLP projector uses mirrors to direct the light in an image, so it is considered to be "reflective." The third type of projector discussed, an LED projector, is named for the light source, not the type of projection technology.How DLP Projectors WorkFirst appearing on the market in the 1980s, D LP pro j e c t ors rely primarily on a DLP chip (called a digital micromirror device, or D M D ) , comprised of up to two million tiny mirrors, no wider thanone-fifth the width of a human hair. Each mirror in this chip is capable of independentadjustment, moving toward or away from the light source to create a dark or light pixel. At this point, however, the image is in grayscale. Color is fed to the DMD by a beam of light thatpasses through a spinning co l or w h e el before it reaches the chip. Each segment of the colorwheel delivers one color. Basic color wheels support red, blue, and green, whereas more advanced color wheels support cyan, magenta, and yellow. While these chips can create up to16.7 million colors, a D L P pr o j ect o r w ith a three-chip architecture can deliver up to 35 trillion colors. After color reaches the DMD, the image is fed through the lens and onto the projection screen.Advantages and Disadvantages to DLP ProjectorsDLP projectors require less maintenance than LCD projectors because they have a filter-freeand sealed chip design, which means dust can‘t settle on the chip and cause an image spot. They are effectively immune to color decay. Furthermore, they are not subject to the misalignments that can occur in LCD projectors with a three-panel design, which require each

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panel to be in perfect position to combine the image at the proper angle. However, DLP projectors with slower color wheels may give off a rainbow effect; flashes of color that appear on the screen, like rainbows. Furthermore, while the chip is sealed, other components are not, so dust can settle on the color wheel and affect image quality. Another disadvantage may be the poor viewing range. Most DLP projectors are not readily compatible with zoom lenses or lens shift functions, which means they are best suited to smaller environments.How LCD Projectors WorkL C D pro j e c t o r s h ave been around since the 1980s, and use the same liquid crystal displays that create the images in watches and other electronic devices. Specifically, most LCD projectorsuse 3 L C D t ec h n ol o g y , a patented system that combines three liquid crystal displays. An imageis created in a multistep process, which begins with the light source providing a beam of white light. The white light is passed to three mirrors (called dichroic mirrors) that are specially shapedto reflect only a certain wavelength of light. In this case, the mirrors reflect red, blue, and greenwavelengths. Each beam of colored light is then fed to an LCD panel, which receives an electrical signal that tells it how to arrange the pixels in the display to create the image. All three LCD panels create the same image, but they have different hues because of the colored light passing through the panel. The images then combine in a prism, creating a single image with up to 16.7 million colors that is passed through the lens and projected onto the screen.Advantages and Disadvantages to LCD ProjectorsLCD projectors have been around since the 1980s, and the technology is more reliable than film projectors. However, they may still require maintenance, as pixels can burn out and dustparticles can interfere with image quality. On the other hand, LCD projectors have no moving parts, as DLP projectors do, and they are generally less expensive than their DLP counterparts.They also support setups in larger rooms where a greater projection distance is needed, because they are compatible with z o o m l e n ses a nd lens shifts.How LED Projectors WorkAs previously stated, L E D pro j e c t o r s a re defined not by the display technology used, but the lighting. In fact, some DLP projectors with "solid-state illumination" technology are actually LED projectors. Another type of projector, the p i co p r o j ector, commonly uses LED technology as well. Pico projectors are essentially handheld devices that use L C oS ( liquid crystal on silicon, which is similar to an LCD panel but reflective rather than transmissive) or D LP t ec h n ol o g y . In these cases, the projector replaces the traditional lamp with longer-lasting and more efficient LEDs, colored in red, green, and blue. In DLP projectors, this also replaces the color wheel technology, instead letting the red, blue, and green LEDs shine directly on the DMD chip.The Advantages and Disadvantages to LED ProjectorsThe LEDs in an LED projector have a much longer life than traditional projector lamps, rated at10,000 or even 20,000 hours as opposed to 1,000 hours to 5,000 hours. As such, the LED light source is meant to last the entire life of the projector without ever needing to be replaced. This isa big advantage because replacing traditional lamps can be a major expense in projector maintenance. There is no warm-up or cool-down time needed because the LEDs are muchmore energy efficient than traditional light sources, and they are also much quieter. This reduces maintenance and operating costs.Factors to Consider when Buying LED, LCD, and DLP ProjectorsWhen buying a projector, consumers should weigh the advantages of each type of device. The differences between the projectors can be summarized in the following chart:

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Projector Type Technology Type Light Source

DLP Reflective LED or standard lamp

LCD Transmissive Standard lamp

LED Transmissive or reflective LED

Beyond the technology used, however, there are other significant differences. L C D pro j e c t ors are typically less expensive for smaller venues, such as home theaters. They also give the user the advantage of a longer throw distance and greater zoom capability, both ofwhich are lacking in many DLP projectors. This makes LCD projectors ideal for larger environments. However, D LP pro j e c t o r s do not suffer the color decay that LCD projectors doand they are easier to maintain because of their filter-free design.D LP pro j e c t o r s w i t h LED t ec h n o l o g y are even simpler because the lamp will not need to be replaced, saving time and money for users. Pi co pro j e c t ors t h a t use L E D t ec h n ol o g y h ave thesame long life, but are designed to be ultra-portable, connecting to s m a r t p h o n es, t a bl et s , andother mobile devices. As such, they do not offer the same high levels of brightness found in larger projectors. They typically have a brightness of less than 200 ANSI lumens, whereaslarger projectors can have a brightness of 1000 ANSI lumens, up to 4500 ANSI lumens or more.

Specialised input and output devicesAutomated systems often use sensors and actuators together to do useful tasks, such as controlling a washing machine.Some computer applications require highly specialised input and output devices. An example is virtual reality (VR), in which the input devices include a wired glove, or data glove, and a VR suitcontaining sensors to detect changes of position. The main output devices are virtual realityheadsets or virtual reality goggles, vibration actuators for wired gloves or VR suits to provide haptic (tactile) feedback for the user, and CAVE rooms in which panoramic images areprojected onto the walls.

Internal memory and storage devices and their usesA computer holds programs and data in two sorts of device:• internal memory — limited-capacity and rapid-access during processing• backing storage — larger-capacity and slower-access to keep data/programs for future use. Computer MemoriesComputer memories are either internal or external. Internal memories are either ROM (read onlymemory) or RAM (random access memory). External memories can take on many forms (and discussed in some detail later).The first part of this discussion considers internal memory systems:

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R e a d on l y m em o r y ( RO M ) ROM holds the instructions for starting up the computer. This type of memory can only be read and cannot be altered (i.e. deleted or written to) and is non-volatile (i.e. it doesn‘t lose itscontents when the computer is switched off). Programmable read only memory (PROM)A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it is permanent. Unlike RAM, PROM's retain their contents when the computer is turned off. The difference between a PROM and a ROM (read only memory) is thata PROM is manufactured as a blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, a special device called a PROMprogrammer or PROM burner is required. E r as a b l e p r o g r a mm a bl e r e a d o n l y m emo r y ( EPR O M ) This is a special type of PROM that can be erased by exposing it to ultraviolet (UV) light. Once ithas been erased, it can be re-programmed using an EPROM burner.Electrically erasable programmable read only memory (EEPROM)An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turnedoff. Also, as with other types of ROM, EEPROM access time is not as fast as RAM. EEPROMsare similar to flash memories (sometimes called flash EEPROM). The principal difference is that an EEPROM requires data to be written or erased one byte at a time, whereas a flash memory allows data to be written or erased in whole blocks.R a n d o m acc e ss m e m ory ( RA M )

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This is a volatile memory (i.e. contents are lost when the computer is switched off). A user can write or delete data as well as read the contents. Before a program can be ran it must first be loaded into RAM which allows the CPU to access the program. Battery-backed RAMs overcome data loss on switching power off, but are outside the scope of these booklets.(NOTE: For completeness, it is worth mentioning that two types of RAM exist called SRAM (static RAM) and DRAM (dynamic RAM) – SRAM doesn‘t need to be constantly refreshed to retain its memory unlike DRAM. Also note that computers use cache which is a portion of memory made from SRAM. Memory caching works since programs usually access the same data or instructions over and over again. By retaining as much information as possible in SRAM, the computer operates more quickly (cache is usually termed level 1, 2 or 3 (termed L1, L2 or L3)).External storage systemsA number of different types of external memory devices are now available. Some of these are described below (hard drives haven‘t been mentioned since these are usually internal; hard drives contain much of the applications software to enable the computer to run effectively). M P 3 ( M PE G- 3) MPEG-3 uses an audio compression technology; it compresses CD-quality sound by a factor of about 10 whilst retaining most of the quality e.g. a 60 Mbyte CD track is turned into a 6 Mbyte MP3 file. Music data is often stored on an MP3 player which plugs into the computer through a USB port. The music data is downloaded to the MP3 player where it is stored in a file. The player has its own internal battery which allows a user to listen to the music files through personal head phones or connect the player to an external sound amplification unit. Variations of MP3 players (e.g. I-pods) exist which use their own file structures when storing music; these require compatible software to enable files to be stored in the correct format.M P 4 ( M PE G- 4) MPEG-4 files are in a format that can hold a mixture of multimedia objects such as audio, video, images, animation, etc. MP4 players again use compression technology to store data in files.They operate in much the same way as MP3 players described above.F l ash m e m ori e s These are non-volatile re-writable memories evolved from the EEPROM; they are often connected to the USB port on the computer enabling a user to transfer files between computers.SD (secure digital) cards are a type of flash memory used in digital cameras and mobile phones. XD (extreme digital) cards are also a type of flash memory used in digital cameras andare similar to SD cards. Compact disks (CD)These are an optical storage media which have basically taken over from the floppy disk. Software is now usually supplied on a CD (in the form of CD-R which can be read only or CD- RW which allows reading and writing of data).Digital versatile disk (DVD)This is an optical system for storing data. It is similar to CD but typically can hold 4.7 Gbyte of data compared to only 700 Mbyte of data on a CD. This is due to dual layering and higherdensity of data storage.Measuring the size of memoryInternal memory capacity is measured in power-of-two multiples of bytes. h e correct binary prefixes are kibi-, mebi-, gibi- and tebi-, which are slightly larger than the corresponding widely used denary prefixes kilo-, mega-, giga- and tera-. However, the use of the denary prefixes is completely appropriate for hard disks.

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Backing storageBacking storage has to be non-volatile and includes:• magnetic media, such as ha rd disks and magnetic tape• optical media, such as CDs, DVDs and Blu-ray discs• solid-state storage devices, such as l ash-based memory sticks• digital storage cards.Different storage media have different characteristics that make them suitable for particular applications:• magnetic storage media

– internal hard disk drive (HDD) is very cheap per gigabyte of storage and provides very high storage capacity with rapid direct access, which makes it suitable for a computer‘s main backingstorage

– lightweight, pocket-sized, external hard disk drive is more expensive, but both removable and highly portable for safekeeping

– magnetic tape drive is very expensive, but a magnetic tape cartridge is a cheap, highcapacity, removable and highly portable storage medium, although access is very slow. This makes it more suitable for making backup or archive copies of the contents of an HDD• optical storage media

– optical discs such as CDs and DVDs have smaller capacities than HDDs or tapes and are also more expensive per gigabyte of storage. They are also direct access media, with rather slower access than a HDD, and are removable and highly portable. The main types of CD and DVD have different suffixes, as follows:

– ROM stands for ‗Read-Only Memory‘ – these cannot be written to, and are suitable for the distribution of music, movies, soft ware and encyclopaedias

– R stands for ‗Recordable‘ – these can be written to just once and then can only be read from,making them suitable for storing music or movies or archive copies of documents

– RW stands for ‗ReWritable‘ – these can be written to and read multiple times, making them suitable for making temporary copies of data files for transfer from one computer to another or regular backup copies

– Blu-ray discs (BD or BR) have larger storage capacities than other optical storage media and a higher rate of data transfer. Although disks are expensive, their cost per gigabyte of storage isnearer to that of a HDD• solid-state storage media

– are electronic and made as integrated circuits or chips, currently using FLASH technology which, like ROM, holds data that are non-volatile, but can be erased and rewritten inlarge blocks

– also known as non-volatile memory– devices often have multi-gibibyte capacities, are very small and portable, and are usually

more robust than HDD or optical media. They include:– USB l ash drives (memory sticks or pen drives)– flash memory chips– digital storage cards (DSCs)– solid-state drives (SSDs).

Mobile phonesMobile phones are examples of very widely used embedded computer systems. Some phones have a wide range of:• input

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• processing (including audio and video recording and playback)• storage• output• communication facilities.More people own mobile phones than computers, so in some parts of the world, people are more likely to access the Internet using a mobile phone than a computer. Smartphones have more flexible operating systems that can run more advanced application programs.

Q u e s t i o n s: 1 The diagram shows a personal computer system. Name the components and classify

them as input, output, storage, communications or processor.

2 Name the data input type and the associated reader used to input the following characters and patterns into a computer.

3 Indicate whether each of the following devices is an input device or an output device:a mouse b monitor

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c plotterd speakere keyboard f scanner.4 Give an example of the use of each of the following:a barcode readerb magnetic ink character recognition (MICR) reader c optical mark reader (OMR).5 Give two ways in which words can be input to a computer without using a keyboard.6 Name three pointing devices and the type of computer system on which they are most often used.7 Describe the input devices used at an ATM machine.8 Name three different types of sensor used to input data in a control application.9 Define the term backing storage and explain why computers need backing storage.10 a Name a storage device used by large organisations with large volumes of data where speed ofaccess is not important.b Describe two applications where it could be used. c What kind of data access does it provide?11 Describe the advantages and disadvantages of the different forms of optical storagemedia.12 What is meant by the term ‗backup‘? Why is it needed?13 ROM and RAM are two types of memory found in computers. a What do the letters ROM stand for?b What do the letters RAM stand for?c What is the main difference between RAM and ROM?d Complete the following statements with ‗RAM‘, ‗ROM‘, ‗backing storage‘.i .......... stores a copy of your work when the computer is switched off.ii .......... stores application programs and data while the computer is running.iii .......... stores programs that must be available as soon as the computer is switched on.14 Complete the following sentences by using the correct words from this list: eight, gigabytes, memory, RAMa A byte is a unit of computer …………… and it consists of ……………. bits.b A school computer may have two ………………….. of ………………….. .15 Indicate which of the following statements are true or false:a ROM stands for Read-Only Memory. b Data can be saved in ROM.c The internal memory of a computer can store soft ware and data.d Data that changes is normally held in ROM.e Data on magnetic tape has to be read serially.f An airline booking system would probably use hard disk drive as backing storage. g A CD-ROM is an optical disk.Answers:2 a This is an example of magnetic ink characters. They are read by a magnetic ink character recognition reader (MICR).b This is an example of a barcode. It is read by a barcode reader.

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c This is an example of a specialised form for data collection by optical mark recognition. It is read by an optical mark reader (OMR).3 a A mouse is an input device. b A monitor is an output device.c A plotter is an output device.d A speaker is an output device. e A keyboard is an input device.f A scanner is an input device.4 a A barcode reader is used at a supermarket checkout to i nd the price for an item byreading the data stored in the item‘s barcode.b A magnetic ink character recognition (MICR) reader is used in a bank to process cheques. The cheque number, bank sort code and account number are printed in magneticink so the MICR reader automatically enters them into the system. The operator has to enterthe amount.c An optical mark reader (OMR) is used to mark multiple-choice exam papers.5 Words can be input to a computer using a microphone with voice recognition software and using a scanner with optical character recognition soft ware (OCR).6 A mouse is used on a desktop computer. A touchpad is used on a laptop. A touch screenis used in a kiosk (e.g. a ticket machine in a train station or airport).7 An ATM machine uses a numeric keypad and buttons at the side of the screen. It may also use a touch screen for some buttons.8 Temperature, pressure and humidity sensors can be used to input data in a control application.9 Backing storage is a long-term non-volatile storage that stores programs and data for future use. Computers need backing storage so that programs and data can be stored afterthe power has been switched off.10 a Magnetic tapes could be used to store large amounts of data where speed of access is not important.b Magnetic tapes can be used in batch-processing applications, such as payroll and utility billing.c Magnetic tapes provide serial data access.11 A DVD drive uses a more precise laser and can fit more data on the disc than a CD, but DVD drives and media are more expensive than CD drives and media. Similarly, Blu-ray discs store more data and are more expensive than DVD media. Recordable media cost more to produce than ROM discs, but allow the user to archive large amounts of data. Re- writable media are even more expensive, but allow the user to record many times on the same disc.12 A ‗backup‘ is a copy of data. It is needed to recover data if the working medium becomescorrupted or damaged.13 a ROM stands for ‗read-only memory‘.b RAM stands for ‗random access memory‘.c RAM is volatile storage and ROM is non-volatile storage. Data in RAM disappears when a computer is switched off – it holds programs and data that are being worked on. Data inROM cannot be changed after manufacture – it holds the computer‘s boot information. d Complete the following statements with ‗RAM‘, ‗ROM‘ or ‗backing storage‘:i Backing storage stores a copy of your work when the computer is switched off. ii RAM stores application programs and data while the computer is running.

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iii ROM stores programs that must be available as soon as the computer is switched on.14 Complete the following sentences by using the correct words from this list:eight gigabytes memory RAM

a A byte is a unit of computer memory and it consists of eight bits. b A school computer may have two gigabytes of RAM.15 Indicate which of the following statements are true or false:a ROM stands for Read-Only Memory – TRUE. b Data can be saved in ROM – FALSE.c The internal memory of a computer can store soft ware and data – TRUE. d Data that changes is normally held in ROM – FALSE.e Data on magnetic tape has to be read serially – TRUE.f An airline booking system would probably use hard disk drive as backing storage – TRUE. g A CD-ROM is an optical disk – TRUE.

EX A MI NAT I O N Q UES T I O N SS um m er 2 0 10 P 11 Q 6 ( a ) Give three different types of device that allow human beings to interface with computersystems.123 [3] (b) Give three automatic data capture devices and give a suitable application for each device.Device 1Application 1Device 2Application 2Device 3Application 3 [6]

S ummer 2 0 10 P 12 Q 9 ) A factory uses a computer system to store information about customers, spare parts and general administration.(a) Spare parts can be identified by selecting from diagrams on a computer screen. Describe what hardware would be needed to allow the parts to be selected in this way. [2](b) The factory needs to buy a new printer. It has decided to buy either a dot matrix printer or an inkjet printer. Discuss the advantages and disadvantages of using both types of printer in this application.Dot matrix printer: AdvantagesDisadvantages [3] Inkjet printer:AdvantagesDisadvantages [3]

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MAR KI NG SC HE MES um m er 2 0 10 P 11 Q 6 (a) Any three from:– keyboard (type in the responses)– touch screen (select options from on screen menus)– mouse/trackerball/touchpad (click on options from a menu)– microphone (speak options)– data gloves/goggles– camera [3](b) Any three different devices + associated application areas, e.g.:– bar code reader – stock control– library systems– OMR/mark sensing – multi-choice papers– questionnaires– touch screens – information desks/kiosks– choosing goods on line– sensors – monitoring chemical plant– central heating systems– cameras – traffic control– security– MICR – reading bank cheques– reading travellers cheques– microphones – telephone systems– games– magnetic stripe reader – reading credit cards– reading security cards– data loggers – weather monitoring– collecting experimental data– OCR – reading in documentsScanner – scanning in photos etc. [6]

S um m er 2 0 10 P 12 Q 9 ( a ) Any two correct input devicesOR input device + correct type of screen– mouse/trackerball + CRT screen/TFT screen– touch screen + CRT screen/TFT screen– light pen + CRT screen [2] (b) Dot matrix printer:Accept a max of 2 advantages and a max of 2 disadvantages: Advantages:– suitable for dirty/dusty/damp atmospheres– cheap to maintain– cheap to run– can operate with continuous/multipart stationeryDisadvantages:– poor print quality– very noisy

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– very limited colours [3] Inkjet printer:Accept a max of 2 advantages and a max of 2 disadvantages:Advantages:– inexpensive to purchase– high quality printouts– can use colours– supported by most operating systems– quietDisadvantages:– run out of printing ink quickly/cartridges run out quickly– price per page/inks are expensive– not suitable for dirty/dusty/damp atmospheres [3]

The following table shows three applications which require specialist output devices.For each application, suggest one possible output device and give a reason for your choice. [6]Application Output device Reason for choice of deviceA visually impaired person using a word processorUsing CAD to design a new engine Monitoring a house for burglars

M ar k i ng S c h eme Application Output device Reason for choice of deviceA visually impairedperson using a word processor

– speakers

– Braille printersfrom word processors

– allows blind people to hearoutput– blind people can read printed output

Using CAD to design a new engine

– plotter

– large monitor

– 3D printer

– accurate print out of large drawings– allows easy editing of drawings– produce working prototypes in resin

Monitoring a house for burglars

– buzzer– light– alarm

– to warn of intruder‘s presencein the building