OUTPUT DEVICES

1.     Monitors:

A monitor (or screen) is the most commonly used output device. They come in many different shapes, sizes and forms. Size of the screen actually indicates the length of the diagonal, so a 17 inch screen has a 17 inch diagonal. The picture on a monitor is made up of thousands of tiny coloured dots called pixels. The quality and detail of the picture depends on the number of pixels that the monitor can display. The higher the number of pixels, the better quality the output.

The two types of monitor that you need to know about are Cathode Ray Tube monitors (CRT) and Thin Film Transistor monitors (TFTs)

Cathode Ray Tube monitors (CRT)

CRT monitor are large and bulky and have a glass screen which makes them fairly robust and difficult to damage. They produce quite a lot of heat so when you have an office with lots of them it could get quite warm. They are also fairly noisy compared to newer TFT monitors.

Thin Film Transistor monitors (TFTs)

TFT monitors used to be very expensive but now the price has come down they are beginning to replace all of the old CRT monitors. Not only do they look much nicer they take up a lot less space. They are quieter than CRT monitors and also create less heat.

They are easier to damage than CRT screens. A few sharp pokes at the screen with a pencil can cause lasting damage. Another disadvantage is that unless you have a very high quality TFT monitor, the colours and contrast are not so good as a CRT monitor and so the picture can look a bit dull.

2.     Printers:

Printers are another common output device. They are used to create a 'hard' copy of your work i.e. something that you can hold, hand to someone else or file away.

Laser printers:

Laser printers are used in many workplaces because they are quiet, they print a large number of sheets very quickly and they produce high quality documents.

They print in the same way as photocopiers. Powdered ink, called 'Toner', is fused onto paper by heat and pressure.

Advantages

• High quality printouts - better than ink-jet or dot-matrix
• Fast printouts - faster than ink-jet or dot-matrix
• Prints very quietly - quieter than ink-jet or dot-matrix
• Cost per page is low - cheaper than ink-jet or dot-matrix

Disadvantages

• Most expensive printer type to buy, especially colour lasers
• Toner is more expensive than ink-jet cartridges
• Expensive to repair - lots of complex equipment inside
• Fairly bulky - larger than ink-jet printers

Inkjet printers:
They are relatively cheap to buy and most of them can combine both black and white and colour printing at the same time.

These printers use cartridges which contain ink. They operate by heating the ink as it flows through the nozzle. The heating process causes a small droplet of ink to form. This is then released as a single dot which forms part of a letter or image. This is why the printouts often come out of an ink-jet printer still slightly wet.

Colour ink-jet printers are ideal for use at home where only a few documents need to be printed and the quality of the printout doesn't need to be perfect.

Advantages

• Cheap to buy - cheaper than a laser printer
• More compact than a laser printer
• Cartridges cost less to replace than toners
• Produce good quality printouts better than a dot-matrix but not as good as a laser
• Speed - faster than a dot-matrix but not as fast as a laser

Disadvantages

• Noisier than a laser printer (but not as noisy as a dot-matrix)
• Colour printing can be extremely slow
• Cost of printouts per page are more expensive than a laser printer
• Cartridges need to be replaced more often than a laser printer
• Ink will smudge while it is still wet
• Colours can become saturated and often don't look the same as on the screen
• If not used for a while, the cartridges can dry out

Dot matrix printers:

These were the first type of printers to be used in homes and schools but they are not used much nowadays.

They are also called 'impact printers'. The print head contains a grid of pins and different combinations of pins are pushed out to form different characters. The print head then hits a carbon ribbon leaving an imprint on the paper. This makes them fairly noisy as you can hear the pins striking the paper.

They are also useful when continuous paper needs to be used for example printing large quantities of invoices or bills. They can be printed onto paper with perforations and then separated by tearing once the printing is complete.

Advantages

• Relatively cheap to buy
• Low operating costs
• Can print on continuous stationary
• Create carbon copies using carbonated paper

Disadvantages

• Print quality is poor and important documents are not suitable to give to managers or customers
• Very slow - slowest out of all three printers
• Noisy - you wouldn't want one of these printing all day in the office
• Cannot produce colour copies

 

3.     Plotter:

Plotters are a specialist type of printer which is able to draw high quality images on very large pieces of paper, for example 3 foot wide by 10 foot long.

They are used by engineers, architects and map-makers to draw plans of buildings, diagrams of machines or large scale maps.

A plotter differs from a printer in that it draws images using a pen that can be lowered, raised and moved across the paper to form continuous lines. The electronically controlled pen is moved around the paper by computer controlled motors.
There are three different types of plotter:
Flatbed plotters - These hold the paper still while the pens move
Drum plotters - These roll the paper over a cylinder.
Pinch-roller plotters - These are a mixture of the two types above

Advantages

·         Drawings are of the same quality as if an expert drew them

·         Larger sizes of paper can be used than most printers can manage

Disadvantages

• Plotters are slower than printers because each line is drawn separately
• They are often more expensive than printers
• They do not produce very high quality text printouts

4.     Speakers:

Most computers are fitted with a small internal speaker which can produce beeping sounds to alert you if you make an error. Computers can also be fitted with a sound card (or chip) which will enable sound to be output through external speakers. These usually produce a much higher quality sound than the internal speaker.

Advantages

• Everyone in the room can hear the output from the computer.
• They can help create an atmosphere or ambiance to accompany a presentation
• They help blind people to use the computer because text can be converted into sound

Disadvantages

• The output from speakers can disturb others who are trying to work
• High quality external speakers can be expensive

USER INTERFACE

The user interface is what we see when we turn on the computer; it consists of the cursors, icons, menus, etc.

User interface may be:

: Command Driven Interface (CDI)

: Menu Driven Interface (MDI)

: Graphical User Interface (GUI)

Command driven interface: An interface through which the user types commands for the computer to carry out tasks Eg: MS-DOS

Advantage:

1.      If the user knows the correct commands then this type of interface can be much faster than any other type of interface.

2.       This type of interface needs much less memory (RAM) in order to use it than other user interfaces.

3.      This type of interface does not use as much CPU processing time as the others do.

4.       A low resolution, cheaper monitor can be used with this type of user interface.

 

Disadvantage:

1.      For someone who has never used a command line interface it can be very confusing.

2.      Commands have to be typed in precisely, if there is a spelling error the command will fail.

3.       If you mis-type an instruction, it is often necessary to start all over again.

4.      There are a large number of commands which need to be learned

Menu driven interface:  This type of interface produce a list of commands or options available within a program and the user can make a selection by using either a mouse or keyboard.
They are extremely easy to use, someone who has never seen the interface before can workout what to do.

 

Advantages:

1.      There are no commands to learn or remember.

2.      Step-by-step options are given so that the user doesn't have to remember anything.

3.       Even if you don't know what to do, you can usually guess you way around the options.

Disadvantages:

1.       A poorly designed menu interface may be slow to use

2.      It can be irritating if there are too many menu screens to work through - users get annoyed or bored if it takes too long.

3.      You often can't go to the exact place you want right at the start. You have to work your way through the menu screens even if you know where you want to get to.

4.      The menu can take up a large part of the screen so you have to keep flicking back and forwards between applications

 

Graphical user interface: An interface that allows a user to communicate with the computer through pictures (icons), Menus, windows etc.

Advantage:

1.      This type of user interface is extremely easy to use, especially for a beginner

2.      It is easy to explore and find your way around the system using a GUI

3.      You do not have to learn complicated commands

4.       There are usually good help facilities provided with GUIs

5.      They let you exchange data between different software applications

 

Disadvantage:

1.      GUI take up a much larger amount of hard disk space than other interfaces

2.      GUI need significantly more memory (RAM) to run than other interface types

3.      GUI use more processing power than other types of interface

AUTOMATED INPUT DEVICE

1.     Magnetic Ink Character Recognition:

Each day, banks process millions of cheques. It would take them far too long to manually enter the data from each cheque. They use a technique called 'Magnetic Ink Character Recognition' (MICR) which enables them to process 300 cheques per minute with 100% accuracy.

At the bottom of each cheque are a series of numbers which record:

• the cheque number
• the bank or building society sort code
• the customer's account number

These numbers are written in a special ink which contains iron particles. This ink is magnetised and commonly called 'magnetic ink'. It can be read by a special machine called a Magnetic Ink Character reader (MICR).

The MICR will only recognise numbers printed in a standard font using the magnetic ink. This provides a high level of security because any attempt to alter the magnetic ink printout with normal ink by writing over it will be ignored. Both the Reader and the magnetic ink are expensive and so are generally only used by banks.

2.     Optical Mark Reader:

OMR sheets are scanned by a special piece of equipment called an 'Optical Mark Reader' (OMR). They detect the presence of your pencil mark by reflecting light onto it. Less light is reflected where a mark has been made. The OMR then interprets the pattern of marks and sends the results to the computer for storage, analysis and reporting.

Advantages

• A fast method of inputting large amounts of data - up to 10,000 forms can be read per hour depending on the quality of the machine used.
• Only one computer needed to collect and process the data
• OMR is much more accurate than data being keyed in by a person

Disadvantages

• If the marks don't fill the space completely, or aren't in a dark enough pencil, they may not be read correctly
• Only suitable for recording one out of a selection of answers, not suitable for text input.
• The OMR reader needs the answers to be on the prepared forms which will all be identical to one another. You can't just pick up a blank sheet of paper and mark your answers on it.

3.     Optical Character Recognition:

An OCR system consists of a normal scanner and some special software. The scanner is used to scan text on a document or piece of paper into the computer. The OCR software then examines the page and changes the letters into a form that can be edited or processed by a normal word processing package.

The ability to scan the characters accurately depends on how clear the writing is.

Scanners have been improved to be able to read different styles and sizes of text as well as neat handwriting.

Although they are often up to 95% accurate, any text scanned with OCR needs careful checking because some letters can be misread.

OCR is used to automatically recognise postcodes on letters at sorting offices.

Advantages

• Cheaper than paying someone to manually enter large amounts of text
• Much faster than someone manually entering large amounts of text
• The latest software can recreate tables and the original layout

Disadvantages

• Not 100% accurate, there are likely to be some mistakes made during the process
• All documents need to be checked over carefully and then manually corrected
• If the original document is of poor quality or the handwriting difficult to read, more mistakes will occur
• Not worth doing for small amounts of text
  
  
  

4.     Barcode Reader:

Most items that are for sale in shops have a barcode printed somewhere on the packaging.

The barcode is a series of vertical bars of varying widths that give information about:

• the country of manufacture
• the name of the manufacturer
• a product code

The barcode does NOT contain the price of the item - this is held on the company database.

A barcode reader is an automatic input device which is used to scan or 'read' the barcode by using a visible red light. The reflected light is translated into digital data that is interpreted by the computer to identify the product and price from the database.

The main advantage of using a barcode system is that any price change only needs to be made to the database and not every single product package.

5.     Magnetic Stripe Reader:

Magnetic strips are usually found of the back of most credit cards, cheque guarantee cards, loyalty cards, membership cards etc.

The magnetic strip can hold personal details about the card number such as account number and name. The strip can contain up to 60 characters, stored magnetically.

To read the data on the card, it is 'swiped' through a Magnetic Stripe Reader machine and the data is read and fed back to the computer.

Advantages

• Simple to use
• Cheap to produce
• Data can be altered if necessary
• Security has been improved by the use of PIN numbers which must be entered into a machine to confirm that you are the rightful card owner

Disadvantages

• Very limited storage capacity for data
• Data can be easily destroyed by strong magnetic fields
• Not always secure as thieves can obtain the readers and read the data on the card.

6.     Biometric Devices:

There is an increasing trend towards using biometric data from people in order to identify them. Finger print and retinal identification are being used in many places now and even facial recognition systems are starting to be introduced.

Special devices are needed to capture the biometric data which is then passed onto the computer for processing and identification.

Biometric authentification methods can be used to identify you at ATMs to withdraw cash.

 

7.     Sensors :

Sensors are used to detect physical quantities outside a computer such as light, temperature and pressure.

They collect data automatically and usually at regular intervals. This data is can either be transmitted immediately to the computer or can be stored for a period of time and a batch of readings sent in one go.

In order to process input from sensors, a device called an 'Analogue to Digital Converter' (ADC) must be connected between the computer and the sensor. This device converts the analogue signals from the sensors to digital data that the computer can process.

INPUT DEVICES

Input devices are used to get data into a system or it is a piece of hardware that is used to enter data into a computer. There are different kinds of input devices. We can use some input devices, such as keyboard, mouse etc to enter data by hand, it is called as manual input device. Other input devices such as bar code readers, MICR etc allow automated data entry; it is called as automatic input device.

1.     Keyboard:
it is the most commonly and widely using input device. It is made up of buttons called 'keys'. The keys are arranged into sections:

·         alphabet keys

·         Function or F keys (F1, F2, F3)

·         Numeric keys (one set above the alphabet keys and a numeric keypad on the right)

·         Arrow keys

Command keys (insert, delete, home, end, page up/down)

A standard keyboard is called a QWERTY keyboard because of the arrangement of the letters of the top row of the alphabet keys.

Advantages

·         Most computers come with a keyboard supplied.

·         People are used to using keyboards to enter data, they need very little training.

·         A skilled typist can enter data very quickly.

·         Specialist keyboards are available e.g. ergonomic, gaming keyboards.

Disadvantages

·         It is easy to make mistakes when typing in data.

·         If you can't touch type, it can be time consuming to enter data.

·         Keyboards are not suitable for creating diagrams.

·         Disabled people often find keyboards difficult to use.

·         Excessive use can lead to R.S.I.( Repetitive Strain Injury).

 2.     Mouse:

             A mouse is also called a 'pointing device' because it enables you to control what happens on the screen by moving the mouse on your desk and pointing, clicking and selecting items on the screen.

A mouse usually has two buttons, a right and left one and also a central wheel which allows you to scroll up and down the page.

Advantages

• Ideal for use with desktop computers.
• Usually supplied as part of a new computer system.
• Most computer users are familiar with them and require little training.
• Works well in conjunction with a keyboard for data entry.

Disadvantages

• They need a flat space close to the computer
• The rollers in mice that use balls can become clogged with grease and grime and lose their accuracy until cleaned.
• Overuse can lead to RSI. 

3.     Touch sensitive pad:

A touch sensitive pad or track pad is an input device which is usually found on a laptop computer. A touchpad can be used in place of a mouse. There are usually two buttons next to the touchpad which are used to replace the left and right mouse button.

Advantages

• Useful for laptops when using a mouse isn't practical
• The pad's position is fixed compared to the keyboard, unlike with a traditional mouse
• Very short finger movements are required to move the cursor

Disadvantages

• Takes practice and skill to control the position of the cursor using the touchpad
• Moist, sweaty fingers can disrupt the signals picked up by the sensors. 

 4.     Joystick:

Joysticks are mainly used for games. Whenever the stick is moved, the cursor moves in a similar direction on the screen.

Advantages

• They give a better gaming experience for racing or flying styles of computer games

Disadvantages

• Some people find joysticks more difficult to control than a traditional mouse.
• Joysticks can break easily if too much force is used on them.

5.     Digital Camera:

A digital camera records images electronically on a memory card rather than on film as did the older models of camera. The images can be downloaded from the memory card onto a computer and then printed, stored or manipulated with a photo editing application.

Most digital cameras let you view the image as soon as you have taken the picture; if you don't like what you see, it can be deleted. The quality of the image is dependent on the resolution or the number of pixels. The more pixels, the better the quality and clarity of the image. Many digital cameras are now capable of taking short video clips along with sound.

Advantages

• No film is needed, no developing costs to view the pictures
• Images can be viewed immediately and unwanted images can be deleted
• Images can be edited, enlarged or enhanced
• Images can be incorporated into documents or added to web sites
• Extra memory sticks can be purchased to store images

Disadvantages

• Digital cameras are generally more expensive than ordinary cameras which use film
• When the memory is full, the images must be downloaded to a computer or deleted before any more can be taken.

6.     Microphone:
 A microphone can be used to input sound.

The sound is detected by the microphone and an electrical signal is transmitted to the computer. Special hardware is used to convert this analogue data into digital data so it can be stored and manipulated.

In the last few years a number of voice recognition systems have been developed. These packages let the user dictate the text into a computer and then convert the speech to text.

Dictating like this can be much quicker than typing but the software isn't perfect and it can interpret a word incorrectly.

7.     Scanner:

Scanners can be used to convert images or text on paper into a digital format that can be used by the computer.

A scanner works by shining a beam of light onto the surface of the object that you are scanning. This light is then reflected back onto a sensor that detects the colour of the light. This is then used to build up the digital image.

Items that are scanned are usually stored in an image format. However, special software - Optical Character Recognition - can be used to convert text on the paper into text which can be edited with a word processor. However, the text doesn't always get converted very well and you could end up with a lot of mistakes.

There are two types of scanner:

• Flatbed scanners
• Handheld scanners

The most popular type is the flatbed scanner. This is probably the one that you use at school. They can scan larger images and are more accurate than handheld scanners.

Handheld scanners are usually only a few inches wide and are held in the hand whilst they are rolled across the document to be scanned. The images produced are generally not as large or as high quality as those captured with a flatbed scanner.

Advantages

• Flatbed scanners are very accurate and can produce reasonably high quality images
• Any image which is digitised by the scanner can then be included on electronic documents
• Images once digitised can be enhanced with a graphics application

Disadvantages

• Images can take up a lot of memory space
• Images lose some quality in the scanning and digitising process
• The quality of the final image is dependent on the quality of the original image.
   

8.     Touch Screen:

A touch screen is the only device which works as both an input and an output device. You view the options available to you on the screen (output) and you then use your finger to touch the option that you have chosen (input).

Touch screens are easy to use and are often found in public places such as cash points at banks, ticket collection terminals at theatres or airports, information centers at museums.

Advantages

• Easy to use, don't need much training
• No extra peripherals such as a mouse are needed
• Software can alter the screen while it is being used, making it more flexible than a concept keyboard which has a permanent overlay.

Disadvantages

• Not suitable for inputting large amounts of data
• Not very accurate - selecting detailed objects can be difficult with fingers
• Tiring to use for long periods
• More expensive than alternatives such as a mouse
  
  

9.     Graphic tablets:

Graphics tablets are often used by graphics designers and illustrators.Using a graphics tablet, a designer can produce much more accurate drawings on the screen than they could with a mouse or other pointing device. Drawings created using a graphics tablet can be accurate to within hundredths of an inch.

A graphics tablet consists of a flat pad (the tablet) on which you draw with a special pen. As you draw on the pad, the image is created on the screen.

Advantages

• It is much more natural to draw diagrams with a pencil type implement (the stylus) rather than with a mouse
• A great level of accuracy can be achieved

Disadvantages

• Not really suitable for general selection work such as pointing and clicking on menu items
• Graphics tablets are much more expensive than a mouse.

 

10.     Concept Keyboard:

A concept keyboard is a flat board that contains a grid of buttons. Each button can be programmed to do whatever you want.

An overlay sheet with pictures or symbols is placed on the grid so that the user can tell what pressing on different areas will do.

Concept keyboards are used when fast input is needed and are ideally suited to selecting from a limited range of choices such as fast food restaurants.

Advantages

• Much faster for making non-text selections such as menu choices on the till of a fast-food outlet.
• The keyboard is waterproof which can be useful where there is dirt or the risk of splashes

Disadvantages

• Poor for text or numeric input - although some keyboards do include a numeric keypad so the operator can enter the amount sold.
• Limited to the options shown on the keyboard.
  
  
  

11.     Tracker ball:

Tracker ball is like an upside down mouse.

The advantage of a tracker ball is that it takes up much less space.

Tracker ball are often seen on laptop computers.