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Input and Output Devices

You should be able to:

  • understand the need for input and output devices
  • describe suitable input devices for a wide range of computer controlled situations
  • describe suitable output devices for a wide range of computer controlled situations
  • discuss input and output devices for users with specific needs 

Input and Output Devices

A computer system processes data. In order to process data it must be first input into the system. This is done by means of an input device.

There are a wide range of different input devices such as keyboards, mice, microphones and so on. Some devices might be used for a single purpose while others are more adaptable to a range of different situations.

Once the data has been processoed it is usualy output in some way. This might be via a monitor, printer or speaker.

Input Devices

An input device is used to get data from the outside world into a format that the computer can process e.g. binary (0s and 1s). Here are some examples of input devices:

Keyboard

A keyboard can be used to enter text and numbers into a computer system. An English keyboard has a QWERTY layout with only minor differences between a British and American version.

Keyboards are the most common input device next to a mouse. They support a wide range of different applications and are simple to use, though they can be slow for those not familar with their layout.

Mouse

A mouse is often user to control the pointer in a graphical user interface (GUI) such as Windows. They can be used to select options from menus, click on icons and select text and images on screen. You can also draw with them, though this can be difficult. You need a smooth desk surface to use them on, so they are not best suited as an input device for portable devices such as laptops where a trackpad is better.

Concept keyboard

On a concept keyboard keys have a specific dedicated function. An example would be in a restaurant where there is a key for each different food item that might be bought. This speeds up the input of data as the operator does not have to remeber codes or prices to type in. Most concept keyboards allow you to change the overlay and reprogram the system.

Optical Mark Reader (OMR)

An OMR device can read marks made on a pre-printed form such as those used to select your lottery numbers, or to answer questions on a multiple choice exam paper or survey.

Because the form is then read by machine large numbers of forms are able to have their data inout quickly and accuratley into the system. The information can also be processed quickly e.g. answers to a multiple choice question paper, once scanned in, can then be automatically marked.

Problems can arise though if the marks are not clear enough or if the forms are creased or damaged. The forms also provide a limited number of responces.

Touch Screens

A touch screen can detect where on the screen surface you are touching. They can do this in a number of ways:

  • A special device and be attached to a normal screen that shines an invisible light across the screen. The system can then detect the X,Y co-ordinates of your finger as it breaks the beem.
  • The screen can have a pressure sensitive film placed over it. These are called 'resistive' touch screens. They are cheaper than capacitive screens, but the film over the screen can make the image look less clear, they can also be slower to respond to touch. However, you can use these screens with gloves on.
  • Finally they can use capacitive technology. These can detect the electrical resistance of skin when it comes into contact with the screen. These are more accurate and can produce a better screen image, but are more expensive and you cannot use them with gloves on as this forms a barrier between the screen and your skin.

Touch screens are often used in mobile devices such as phones and tablets where you would not have space for a traditional keyboard. On these devices a 'virtual' keyboard might be used. You can also find touch screens in many shopping centres and tourist attractions where users can go to find information.

Barcode reader

A barcode reader is used to read barcodes which can be found on products in shops. The barcode uses lasers to identify the position and thickness of the bars, this data then generates a unique code which can be used to search a database to locate the product information. A barcode does not contain the price of the product, as the same can of soup can be different prices in different stores.

The benefit of barcodes are that they can be read quickly and accuraty, and pecause a human is not inputting the data via keyboard fewer errors are made. A barcode can be read in any orientation.

Problems arise however, if the barcode is damaged or greasy. In this case the operator can type the numbers in below the barcode. The last number of the barcode is a check digit which is used to ensure the code was typed in correctly. 

Optical Character Recognition/Reader (OCR)

OCR is the process of scanning in a printed document and converting it into editable text. This differs from scanning in a normal document which would be stored as an image file.

Suppose you were to lose the electronic copy of an essay you had written, but still had the printed copy. With OCR you could scan the document in and return it to a text file where you can edit it just like before.

Most scanners will come with free OCR software to let you do this. The advantages of OCR are obvious, however, it is not always accurate the process of recognising letters is not easy and the software can confuse certain letters such as '5' and 'S' or '0' and 'O'. Some fonts are also easier to read than others.

Magnetic Ink Character Recognition (MICR)

A MICR reader is used to read the numbers printed on the bottom of cheques. The digits are printed using a special ink in a special character set (font). The ink is magnetised which makes reading the digits more accurate. It also makes the system more secure and the cheques are harder to forge as the ink is not so easily available.

Magnetic Stripe Reader

A magnetic stripe can be found on the backs of many credit cards. They can also be used on security cards to gain access to rooms etc.

Data is encoded magnetically on the strip and read by a machine as it is swiped.

As extra seurity this is sometimes combined with a code needed to be typed in after the card has been swiped. While using a magentic stripe can speed up entry of data they can sometimes be tempremental, requiring several swipes for the card to be read, perhaps because the user swipes the card too quickly, or because the stripe is damaged in some why. Data can also be lost from the stripe if it is placed near a magnet.

Smart Card Reader

On smart cards you will find a small, often gold chip. This chip can hold far more information than a magnetic stripe. It is also harder to copy as the data is encypted.

Smart card chips can now be found on almost all credit cards. They make it harder for someone to use your credit card if it lost, as without your PIN (personal identification number) they cannot use the card.

Other companies such as Sky use these cards to control the services that you can access from their devices.

Microphone

A microphone can be used to input voice or sound data into a computer system. Sound occurs as an anologue wave naturally, so a microphone must be plugged into an analogue to digital converter (ADC) such as a sound card to convert the signal into digital format (0s and 1s).

A physically impaired person might use a microphone to issue command to a computer or to enter information if they cannot use a keyboard. This would require voice regonition software. This software can be highly reliable if trained to recognised a persons voice. It can also been frustrating if the system has trouble with your accent or speed of speech.

 

Below is an example of the frustration you might experience using a voice recognition system:

Sensors

Sensors can be used by computer systems to take readings from the real world. There are many different types of sensors:

  • Temperature sensors
  • Tilt sensors
  • Proximity sensors
  • Light sensors
  • pH sensors

These sensors could be used in part of a science experiment or in devices you would find in the home such as a central heating system. Your central heading system probably has a thermastate which can measure the temperature in a room, if the temperature drops the system detects this and increase the flow of hot water to the radiators, if the temperature is too high it decreases it. This is an example of a feedback loop where the output of a computer system can effect the input.

Output Devices

An output device is used to get data stored in the computer (in binary format) into another format, often one which a human can understand.

Here are some examples of output devices:

Monitor or VDU

A monitor is perhaps the most common output device. It is used to display visual information from the computer system. The early computer monitors could only display text, and often only in one colour. Modern monitors are capable of displaying millions of collours at very high resoltions.

TFT monitors use liquid crystal technology to display the images, these are very flat, take up less desk space and require less power (which is why they were commonly first used on laptops). CRT monitors use valve technology and can be big, heavy and require far more electricity. However, for some tasks such as graphics design CRT monitors can give better colour representation.

Laser Printer

A laser printer uses a laser to charge electrons on a drum which then attract the powered toner the printer uses. Heat is then used to fuse the toner powder to the paper (this is why the paper can sometimes feel warm when first picked up).

Laser printers have recently come down in price and a cheap laser printer can be picked up for £70. However, the toner is often more expensive to offset the loss the manufacturer might be making on the printer itself.

However, if a business spends around £500 on a printer then printing costs can be reduced and would be cheaper than using an ink-jet printer. Therefore most large businesses will use laser printers for producing large volumes of printing.

Ink-jet Printer

An ink-jet printer 'squirts' small dots of liquid ink onto the paper. By combining different colours a good quality printer can produce photo-quality prints.

Ink-jet printer can be cheaper than laser printers, but in many cases are more exepnsive the run as the ink can be expensive (often costing more than the printer itself!).

Dot-matrix Printer

This type of printer used to be the most common type of printer found in the home or office until the early 1990s. They were cheap (though not very fast and rather noisy).

They work by moving a print head (with pins which can be quickly pushed forward or retracted), these pins make contact with an inked ribbon which then produces the letters on the page.

Dot-matrix printers are impact printers, meaning than the printing device makes contact with the page. This means than carbon copy paper can be used so two or three copies of the same document can be printed at the same time. Businesses often use this feature for invoices and delivery notes. Because so few people buy dot-matrix printers now, they are often more expensive than laser printers.

Plotter

A plotter is a special type of printer. You can get flat bed plotters (like the one in the picture) or drum plotters (which often use ink-jet technology).

In a flat bed plotter, a large piece of paper can be placed on the bed a pen is then moved in an arm up and down and left and right across the paper producing a line drawing. These can be used for producing architectural plans and other such line drawing.

A drum plotter when using ink-jet technology can produce large scale images, much larger than say an A3 sized printer could.

Speakers

Speakers can be used by a computer system to output sound. Sound data inside a computer is stored in digital (binary) format, so in order to be output must first be converted into analogue data. This is done by a digital to analogue converter (found in your PCs sound card).

Actuator

An actuator is a device like a motor. A computer system can use a motor to control real world objects such as doors, car etc.

A simple system might be a remote control buggy which you control with a computer program, the computer program can send instructions to turn the motor on, off, speed it up or slow it down.

Most modern planes use fly by wire systems where the command given to the plane by the pilot are interpreted by the onboard computer system and this is then converted (outputted) into the changes made to the planes flight surfaces such as flaps, ailerons etc.

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