GCSE ICT

1. Study...Study...Study GCSE ICT Revision PowerPoint

2. 1 Computers, Data and Information A computer is aninformation processing machine. Computers process data to produce information. The sets of instructions that humans give computers are called programs or software. Software that carries out a particular type of task for a user is often called applications software.

3. Three stages of computing: 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. The most commonly used input devices are the mouseand 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. Most commonly used output devices are a monitor or visual display unit (VDU) and the printer.

7. Data and information Data is any collection of numbers, characters or symbols that has been coded into a format that can be input into a computer and processed. Data on its own has no meaning, or context. It is only after processing by a computer that data takes on a context and becomes information.

8. Computer Systems Hardwareis 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.

10. The central processing unit (CPU) This is the part of the computer where the searching and sorting of data, calculating and decision-making goes on. The CPU contains the Main Memory, the Control Unit and the Arithmetic and Logic Unit (ALU).

12. 2 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

13. 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.

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

15. 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.

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

17. Digital camera Can store 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.

18. 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.

19. Concept keyboard A concept keyboard is a flat board with a grid of programmable keys on its surface. 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.

20. 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.

21. Microphone A microphone is used to input sound into a computer system. Microphones are often used for voice recognitionsystems 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.

22. 3 Direct Input Methods • Methods of capturing and entering data directly without any need for human intervention. • Used when very large amounts of data need to be input quickly and accurately.

23. Optical Mark Recognition (OMR) • OMR uses an input device 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

24. Magnetic Ink Character Recognition (MICR) • MICR uses an input device 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

25. 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

26. 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

27. Magnetic stripe readers • A magnetic stripe is a thin band of magnetic tape • Often on the back of a credit or debit card. • Magnetic stripes can hold only a small amount of data • 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

28. 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.

29. Data logging • Data logging is a way of using a computer to automatically collect data over a period of time without any need for human supervision • Used in weather monitoring stations and in science experiments

30. Applications of data logging • Monitoring hospital patients • Collecting weather data • Monitoring air quality

31. 4 Checking data Data stored on a computer is only useful as long as it is correct and up-to-date. it is important to check data when it is entered to make sure it is both sensible and correct. There are two methods that can be used to check data when it is input. These are called verification and validation.

32. Verification Verification is checking to make sure that data has been entered correctly. Verification is often carried out by getting two users to enter the same set of data at different computers. Two sets of data are compared to check that they match up. Any data that does not match up is rejected.

33. Validation Validation checks are carried out by software to make sure that data which has been entered is allowable and sensible. There are many different types of validation check that software can make on data. We will now look at some of these in more detail.

34. Range check Range checks are used to check that data is within a certain range of numbers or a specific set of values. Example: If examination marks for a group of students was being input a range check could be used to make sure that each mark was greater than or equal to zero and less than or equal to the maximum possible mark.

35. Type check Type checks are used to check that the correct type of data has been entered in a field. Example: If numeric data is being input a type check could be used to make sure that text data isn’t entered by accident. Length check Length checks are used to check that input data contains a certain number of characters. Example: If a value in a certain field had to contain five digits and only four digits were input, an error message would be given to the user.

36. Presence check A presence check is used to make sure that a value has actually been entered in a field. A presence check makes sure that data is present in a field where it is compulsory that a value is needed.

37. Check digit Check digits are used to validate long numbers that have a lot of digits in them. A check digit is an extra digit placed at the end of long number that can be used to check if the number has been input correctly. Check digits are often used to check numbers that have been input using direct data entry devices such as bar code scanners or light pens.

38. 5 Storing data Data storage devices can be divided into 2 main categories: Backing storageis used to store programs and data when they are not being used or when a computer is switched off. When programs and data are needed they are copied into main memory but also still remain on backing storage. Magnetic tape drives, floppy disk drives and hard disk drives are all examples of backing storage devices. The Main Memorycontains two types of memory chip called ROM and RAM which hold program instructions and data.

39. BITS and BYTES Computers store and process data using binary numbers. A single unit in binary is called a bit which stands for binarydigit. Computer memory is measured in bytes. One byte is made up of eight bits. One byte can store one character. The eight bit binary code in this byte represents the letter A

40. The size of a computer’s memory is normally measured in kilobytes (Kb), megabytes (Mb) or gigabytes (Gb). The table below shows some of the main units of size that we use to measure computer memory.

41. Random Access Memory (RAM) RAM is the computer’s ‘working memory’. RAM temporarily stores programs and data that are being used at a given time. The contents of RAM can be changed and are lost when the computer is turned off. Memory which is wiped clean when the computer is turned off is called volatile memory.

42. Read Only Memory (ROM) The main use of ROM memory chips in a computer is to store the program that runs when the computer is turned on which loads the operating system (e.g. Windows 2000) from disk. The contents of ROM can’t be changed and aren’t lost when the computer is switched off. Memory which isn't wiped clean when the computer is turned off is called non-volatile memory.

43. Hard disk drives A hard disk is a circular metal disk coated with magnetic material and usually sealed in a hard disk drive inside the computer. Some hard disk drives are not permanently fixed inside the computer but are removable.

44. Floppy disks A floppy disk a circular piece of plastic coated with a magnetic material and protected by a hard plastic cover. The size of a floppy disk is measured in inches. Modern floppy disks are 3½ inches wide. A standard floppy disk can store up to 1.44 Mb of data.

45. CD-ROM CD-ROM stands for compact disk read only memory. A CD-ROM looks just like an ordinary compact disk. CD-ROM disks come with information already on them and are read only. This means that the information on a CD-ROM cannot be erased or changed, and no new information can be saved.

46. Writeable CDs Writeable compact disks are supplied blank and can have data put onto them using a special read/write CD drive. There are two main types of writeable compact disk; • WORM(Write-Once, Read-Many) disks which can have data written to them just once. • Magneto-Opticaldisks which can have data written to them any number of times just like a hard disk.

47. Digital versatile disk (DVD) • DVD is the latest way of storing data • DVD discs are expected to replace ordinary compact discs and video tapes in the future • A DVD disc can store up to 17 gigabytes of data. This is enough storage space for at least four full-length feature films!

48. Magnetic tape Magnetic tape comes in two forms; tape reels, and cassettes or cartridges. Large tape reels are used to make backup copies of programs and data on large mainframe computers. The main advantage of using magnetic tape as backing storage is that it is relatively cheap and can store large amounts of data.

49. File compression File compression software can be used to make files smaller so that more data can be stored in the same amount of space on backing store. When a compressed file on backing store needs to be used it must be decompressed.

50. 6 Output Methods The output devices that you are probably most used to will be a monitor, and printer. Another sort of output that you will have experienced when using a computer is sound, which is output through a speaker.