Inputs and Outputs

Input and output devices are peripherals, and whilst inputs are used to input data and instructions into a computer, output devices either transfer information to another system or medium, or somehow get into the outside world so it can be seen or heard by humans.

                One of the most important input devices in computing is the mouse, which is used to give basic commands to the computer within some kind of graphical interface, which is a type of operating system.  Either using a wireless sensor or traditionally a motion-tracking ball, the mouse registers movement of the mouse along an XY axis to detect its position in relation to where it should be on the screen.  Even more important is the keyboard, which is a device that was traditionally used to input text or numbers.  As each key is pressed it relates it to a command for something (e.g. delete) to occur or ASCII code (binary number) so that a number or letter may be displayed.

  Using a microphone to have a voice input is also considered to be important in modern times, as voice recognition means that a computer can relate what is said to a command using software.  Different commands like ‘start’ or ‘save’ can be given, in addition to the ability to dictate information to be stored, for example in a word document.  Additionally contemporary digital cameras and camcorders may transfer photos and videos to a computer using a USB connection or a by plugging its memory card into the computer.  These devices detect light intensity using charged-coupled-devices to build up images.

  Two other devices used frequently nowadays are Tablet PCs and touch sensitive devices such as E-readers.  Touch screens let a user interact with a piece of software through using touch, and work by beaming infrared light across the screen, and when a beam is broken it can detect where this has occurred because of photoelectric sensors at the ends of the beams.  Circuits connected to these sensors then relate where the beam has been broken to an XY coordinate, which the computer then relates to a specific command.

  On the other hand, graphics tablets work in a different way as each time the pen (known as a stylus) is pressed against the screen it activates a microswitch, which causes the computer to register its movement, and the electronics in the screen itself detects the pen touching the screen and the pressure applied.  An alternative version of these graphics tablets work by using a puck with buttons and cross hairs.  After a line drawing is done the puck is used to align the drawing with the cross hairs which are detected by the tablet.  The graphics tablet then detects the position of these cross hairs and creates a digital representation of it. 

  Another type of input device is a reader, and one example of this is barcode readers for which reflect light onto black and white striped barcodes and register where the light has and has not shined back, which is detected by photoelectric sensors, and is translated from an optical form to a binary number.  This binary number is then generally related to an item in a database, such as a food item in a supermarket. 

  A different type of readers are magnetic strip readers that scan the charged magnetic strips on the back of cards which contain binary digits, and relate these to a specific number to transfer a small amount of information such as an identification code.  However many of these are now being replaced by the more secure smart card readers which read the magnetic strips and decrypt encrypted data on a chip, which can be used for a security code.  Each chip contains a small processor, some ROM and RAM which stores temporary data and EEPROM which stores permanent data.  The other type of reader is a Radio Frequency Identification Reader, which receives information from a transponder that contains an antenna for transmitting information, and a microchip to conduct this process.  These are often used for security purposes, such as identifying luggage in an airport.

                Lastly, scanners beam light across a page to attain a digital image or form of an object, generally something on a piece of paper.  Flatbed scanners work by moving light sensors and a very bright light below a pane of glass to detect where the light is absorbed and where it is reflected to build up a picture of what has been scanned.  A colour scanner will contain differently coloured lights are used to detect the intensity of the primary colours in what is reflected to identify each shade and colour mix in each pixel, although a black and white only has a bright white light, and as such only different shades and not colours can be distinguished.

  Optical Mark Readers shine light on a page and detect where light has been reflected and where it has not, to identify where a page has been marked.  It converts the photoelectric readings into binary numbers to identify ‘yes’ and ‘no’.  Where a mark has been made it will often be a ‘yes’ (1), and where there is no mark a ‘no’ (0).  On the other hand Optical Character Readers use optical scanners to recognize characters such as letters or numbers and translate them into binary digits, which can either be used for uploading handwritten documents to a computer or organize documents.

  The other three types of scanners scan fingerprints, and the retina and iris in the eye.  These all work similarly as they shine light at the target and analyze what is sent back.  However, whilst the fingerprint scanner uses light to judge the depth of depressions dependent on the time it takes them to return, iris scanners analyze what is reflected and record a pattern whilst retina scanners convert the reflected light into a unique image of the eye.  It must also be noted that both iris and retina scanners use low intensity light for safety purposes, and that retina scanners use infrared light to create a more accurate picture.

                One of the main types of output is a display, of which there are three types.  Cathode Ray Tube (CRT) displays work by using a light tube which beams electrons against a phosphor coated screen that then reflects what is sent by the tube, making it visible on the screen.  This process happens many times per second to make sure that the image does not appear to flicker.  However, colour CRT displays work by using three sources of electrons – red, blue and green to create different intensities of these colours and mix these colours to create others on screen.

  Liquid Crystal Displays work by having their liquid crystals polarized by a source of electrons to create different colours.  These monitors may also contain filters to vary the shades of colours, and each liquid crystal also contains a TFT and capacitor which are responsible for changing the polarization of the light.  Because of the way they do not project an image they use less energy and are as such more efficient.

  Alternatively, plasma screens have a gas which is superheated to become plasma and release ultraviolet light.   They have light shined through this to create colours in a similar way to LCDs in the pixels.  However, plasma screens often have contrast issues because they have to be constantly primed by having a low voltage applied to each pixel, or otherwise they would respond slowly.  Additionally they are inefficient because they create a high amount of heat, though are used regularly for large screens.

  Two other practical output devices are speech output where words on the screen are outputted as sound, and electronic paper which uses beads that respond to when an electrically charged pencil is moved across them to show what has been inputted.

  Finally, printers are an output device used to print what is on a computer’s display onto paper.  An impact printer works by impacting different pins in a pattern against an ink ribbon, and then printing this pattern onto the paper.  Although they are noisy and slow, they are efficient and robust.  The three types of non-impact printers are inkjet printers, laser printers and plotter printers.  Inkjet printers fire differently coloured inks on the page and mix them to create the desired colours, printing one line at a time.  They create different colours out of cyan, magnenta, yellow and black.

 Laser printers use a similar technique to a photocopier through attracting toner to charged areas, and plotter printers work by using a pen like device which moves across the page to draw on the paper – and are used for large scale items.  They work by moving across the X and Y axis at the same time and the paper may be moved by the drum.  All three types of non-impact printers work by using a non-physical contact such as through charging the paper.