Computing is not just about using complex applications software in research and development, or for playing computer games, or storing and manipulating large databases of information. One important area computing is used is communication between the other computers and the ‘outside world’, e.g. the internet.
This communication with external devices is in the use of input/output ( I/O ) devices, for example the connection between the computer and the printer, or the keyboard and the mouse. In more applied applications this may be monitoring a chemical process or a manufacturing process where information is constantly being fed to and from the computer.
Visual Display Unit ( VDU ) Is an output device.
The Image produced is onto the face of the cathode ray tube ( CRT ), the display is refreshed at 50-60 Hz.
The image displayed on the VDU is made up of horizontal and vertical dots called pixels. The number of pixels that can be displayed at one time is called the resolution. The resolution is in general represented by a pair of numbers e.g. 640 x 480 = 307,206 pixels. The quality of the colour of each pixel depends on the colour depth. The character images on the screen are stored as bits in a ROM, called a character generator. Atypical monitor can display 24 lines of text, each line can display upto 80 to 130 characters.
The display is an analogue device, and the information to sent to the screen is in a digital form. It can be seen that in order to store this information the capacity of the primary memory must be sufficient this can be in the order of 16Mbytes, in some cases. The importance of this is not just in the quality of colour, but storage if the images. The refresh rate is an important consideration. This is the number of times per second the video card can send a signal to the monitor and the monitor is able to repaint the screen. Refresh rates are normally measured in Hertz( Hz), the unit of frequency. If this rate is too low then you get flicker. Another, important consideration of the VDU, is the interlacing, capacity . Interlacing is where half the screen is repainted, and hence the refresh rate can be doubled.
There has become a need from the consumer to have better video cards and better VDU’S/Monitors. This rise has been due to the advent of the DVD and the full colour motion picture and 3D games for the PC, but the expense is the need for memory. The other for of display is the Liquid Crystal Display (LCD).
Keyboard
The keyboard provides the main method of the user communicating with the computer. The keyboard is a collection of key switches or pressure sensitive pads, which are arranged in the same configuration of a typewriter keyboard, QWERTY, originally designed to prevent the jamming of the print hammers in type writers.
There are two methods by which the computer can recognise the fact a key has been struck:
Keyboard Encoder, gives a unique code for each key(ASCII).
Keyboard Scan, the whole of the keyboard is examined to see which key has been pressed.
Mouse, function to provide an input to the computer, essential for windows word on the computer. There are analogue and optical operated mouse.
Printers
Printers convert electrical output from the computer to a HARDCOPY or SOFTCOPY.
Printers can be essentially classified into two groups the first group is :
Impact Printers
Many of these are no longer used.
Chain
Dot Matrix
Daisy Wheel
Golf Ball
Non -Impact Printers
Injet
Laser
Dot Matrix
Each of the characters in the dot matrix is formed by a matrix, e.g. 7 *5. This form of printer has been very popular in computing applications.
Ink Jet
In this type of printer, as the name suggests produces the characters by spraying drops of ink onto the paper. Colour printing is achieved by combining the primary colours, red, green and blue.
Laser Printer( black and white/colour)
Laser printers are common place in most computing environments. These printers work in a similar way to photocopiers. Basically the process of creating a character involves a drum, a laser and a toner to form the final image onto paper.
The obvious disadvantage is, in general applies to most external devices, the need for external drivers, The others may be the cost of replacement ink.
Scanners
Scanners digitises the image, text or picture. The image can the be stored in the computer.
Interfacing
Although computing I/O devices have been briefly discussed, in order for this communication to occur there must be the correct method of initiating the process of
of interfacing . Interfacing, is allowed only if the correct protocol is used to allow input/output, (I/O) to occur. Information external to the computer must be gathered, and the be “carried” to the processor, via the data bus network. The bus network is both external and internal ( on the motherboard of the computer), hence to create a reliable network for communication both must be able to connect the two together and hence be able to communicate with each other.
