Computer Systems

1. Computer Systems

2. The three stages of computing are input, processing and output. A computer works through these stages by ‘running’ a program. A program is a set of step-by-step instructions which tells the computer exactly what to do with input in order to produce the required output.

4. Input This stage of computing is concerned with getting the data needed by the program into the computer. Input devices are used to do this. The most commonly used input devices are the mouse and the keyboard.

5. Processing The instructions about what to do with the input are contained in a program. During the processing stage the computer follows these instructions using the data which has just been input. What the computer produces at the end of this stage is called output.

6. Output This stage of computing is concerned with producing the processed data as information in a form that is useful to the user. Output devices are used to do this. The most commonly used output devices are the screen, which is also called a monitor or visual display unit (VDU) and the printer.

7. Computer Systems Hardware is the name that is given to any part of a computer that you can actually touch. An individual piece of hardware is called a device. The basic hardware of any computer consists of a central processing unit (CPU) along with input, output and backing storage devices.

8. Manual Input Methods Manual input devices are used by people to enter data by hand. Keyboard Pointing devices Joystick Digital camera Touch screen Scanner Concept keyboard Graphics tablet Microphone Light pen

9. Keyboard The keyboard is the most common type of input device. Ordinary computer keyboards have their keys arranged in a similar way to those on a typewriter. This way of arranging the keys is called QWERTY because of the order that the keys appear in on the first row of letters.

10. Pointing devices A mouse is a pointing device. It is the next most common type of input device after the keyboard. Touch pads and trackballs are also types of pointing device. They are often used instead of a mouse on portable computers.

11. Joystick The main use of a joystick is to play computer games by controlling the way that something moves on the screen. Joysticks can be used to control movement from side-to-side, up-and-down and diagonally. A joystick will also always have at least one button on it which can be used to make something happen like making a character in a game jump or fire a gun.

12. Touch screen A touch screen can detect exactly where on its surface it has been touched. Touch screens are used in a lot of fast food chains and restaurants because they are easy to keep clean and re-program if changes need to be made to the menu.

13. Digital camera A digital camera can store many more pictures than an ordinary camera. Pictures taken using a digital camera are stored inside its memory and can be transferred to a computer by connecting the camera to it. A digital camera takes pictures by converting the light passing through the lens at the front into a digital image.

14. Scanner A scanner can be used to input pictures and text into a computer. There are two main types of scanner; Hand-held and Flat-bed.

15. Concept keyboard A concept keyboard is a flat board with a grid of programmable keys on its surface. A single key or a group of keys can be set up to carry out a particular task. Paper overlays are placed on top of the keyboard with pictures drawn on them to represent what will happen if the keys in a certain position are pressed. Concept keyboards are often used with young children in primary schools who can’t use an ordinary keyboard very well.

16. Graphics tablet A graphics tablet consists of a flat surface and a pen, or stylus, which can be used to produce freehand drawings or trace around shapes. When the special pen touches the surface of the graphics tablet data about its position is sent to the computer. This data is used to produce on the screen an exact copy of what is being drawn on the surface of the graphics tablet.

17. Microphone A microphone is used to input sound into a computer system. Microphones are often used for voice recognition systems which convert sounds made by a user into commands that the computer can carry out. Systems like this are very useful for people who can’t use ordinary input devices such as the mouse and keyboard. As computers become more powerful in the future, voice recognition will be a much more common input method for all computer users.

18. Light pen • A light pen is a small ‘pen-shaped’ wand, which contains light sensors. • It is used to choose objects or commands on the screen either by pressing it against the surface of the screen or by pressing a small switch on its side. • A signal is sent to the computer, which then works out the light pen’s exact location on the screen. • The advantage of a light pen is that it doesn’t need a special screen or screen coating.

19. Direct Input Methods • Methods of capturing and entering data directly without any need for human intervention. • Sometimes called direct data entry, or DDE for short • Used when very large amounts of data need to be input quickly and accurately.

20. Optical Mark Recognition (OMR) • OMR uses an input device called an optical mark reader to detect marks made in certain places on specially printed forms. • A fast input method, used where large amounts of data need to be input quickly. • Used to input data from things like answer sheets for multiple choice exams and registration forms in schools • Also National Lottery forms

21. Magnetic Ink Character Recognition (MICR) • MICR uses an input device called a magnetic ink character reader to input characters that have been printed in special magnetic ink • Banks use MICR to process cheques • Banks use this method of input for processing cheques because it is very secure • The equipment needed to print and read characters in magnetic ink is very expensive

22. Optical Character Recognition (OCR) • OCR is the use of an ordinary scanner and special software to convert text in a scanned image into a format that can be edited by word processing software • Text must be printed or written very clearly • Used for the reading of typed postcodes • OCR depends on the shape of the marks whereas OMR depends on the position of the marks

23. Bar codes • A bar code is a set of lines of different thicknesses that represent a number • Bar Code Readers are used to input data from bar codes. Most products in shops have bar codes on them • Bar code readers work by shining a beam of light on the lines that make up the bar code and detecting the amount of light that is reflected back • Bar codes represent a code number for a product

24. Magnetic stripe readers • A magnetic stripe is a thin band of magnetic tape • Often on the back of a credit or debit card, identity cards and electronic key cards in hotels and businesses • Magnetic stripes can hold only a small amount of data and are quite easy to forge • In the next few years magnetic stripes will be replaced with smart cards which store much more data on a small microchip built into the surface of the card

25. Sensors • Sensors are used to detect physical quantities outside a computer such as temperature, pressure and light • To be able to process input from sensors a device called an analogue-to-digital converter must be connected between the computer and the sensors. This device converts signals from sensors into digital data that the computer can process.

26. 5 Output Methods Before any output can be produced by a computer it must have an output device connected to it. The output devices that you are probably most used to will be the screen, or monitor, and the printer. Another sort of output that you will have experienced when using a computer is sound, which is output through a speaker.

27. Monitor A monitor or screen is an output device that can display graphics and text and video. The picture on a monitor is made up of thousands of tiny coloured dots called pixels. The quality of the output on a monitor depends on its resolution. The resolution of a monitor depends on the number of pixels that it can display.

28. Dot matrix printers A dot matrix printer forms characters and graphics on the paper by producing patterns of dots. If you look closely at a print-out from a dot matrix printer you will see the tiny dots which make up the printout. The part of the printer which forms the patterns of dots is called the print head. The print head is made up from pins which are pushed out in different arrangements to form the various patterns of dots needed.

29. Inkjet printers Inkjet printers work like dot matrix printers because the printouts that they produce are made up of patterns of very small dots but the print head has a set of tiny holes rather than pins. As the print head moves across the paper ink is forced out through the holes to form the image. Inkjet printers are very quiet to operate and can produce good-quality printouts of both graphics and text. Relatively cheap colour graphics can be printed using a colour inkjet.

30. Laser printers Laser printers give very high-quality printed output of both text and graphics very quickly and quietly. They are generally more expensive to buy than inkjet printers and the toner cartridges are more expensive. They are very suitable for large volume printouts because of their speed.

31. Plotters The main difference between a plotter and a printer is that a plotter uses a pen to draw the computer output onto the paper. Some plotters use a set of coloured pens to produce colour output. Plotters produce very accurate drawings and are often used in computer aided design or CAD.

32. Speakers Computers can output music, voices and many other complicated sounds using speakers. To be able to output sound a computer needs to have a special circuit board inside it called a sound card.