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Computer Science (security and data management (security (Important to…

- - - - Ensures that data/programs do not corrupt each other
      - Ensures that all programs and data including itself is stored in correct memory locations
    - - Ensures that different processes can utilise the CPU and do not interfere with each other or crash
      - On a multi-tasking O/S ensure that all tasks appear to run simultaneously
    - - Creates and maintains Filing system such as FAT or NTFS (accepted but not expected)
      - Ensures that data is stored and can be retrieved correctly from any disk drive
      - Organise files in a hierarchical directory structure.
    - - Communicates with and receives data input to a keyboard/mouse/other valid input device
      - input and output devices
      - Communicates with and sends data output to a printer/monitor/other valid output device
    - - Data is stored on hard disc/in memory/stored in a queue
      - Document is printed when printer is free/in correct order
      - Benefit of spooling – user can carry on working/log off when waiting for job to print
    - - Allows creation and deletion of user accounts
      - Allows users to logon and change passwords
  - - - File transfer is the ability to transfer data from one location to another. This can be done by simply copying a file from one folder (directory) to another, or from one storage medium to another.
      - You may wish to carry out either of these tasks in order to organise your files better, using subfolders or to back-up your work onto a secondary storage device, such as a flash memory stick.
    - - Formatting is the process of preparing a disk for use.
      - During this process, a new file system is set out on disk and all data may be erased in readiness for new data to be stored.
    - - Compression is the process of making a file size smaller.
      - This may be advantageous as it allows more data to be stored on the disk and files may also be transferred more quickly.
      - There are two methods of achieving disk compression; one is software based and the other hardware based.
  - - - Drawbacks
        
        GUIs take up a much larger amount of hard disk space than other interfaces
        
        Computing experts may find a GUI slower than a command line interface
        
        Requires a large amount of memory
        
        Is relatively processor intensive
      - shortcuts/hot keys
      - Assistants/help files/ tutorials
      - Menus
      - Windows
      - A GUI is a type of interface that allows users to interact with a computer system through graphical icons
      - GUIs were introduced to help users, especially beginners, to use a computer systems as Command Line Interfaces (CLIs) were found to be difficult.
      - Icons
      - Pointers
      - Favourite settings/change environment/customisation
      - task bar/ribbon bar/tabs/customised toolbar
      - Benefits
        
        Data between different software applications is easily exchanged
        
        Uses windows, icons, menus and pointers
        
        Intuitive
        
        Easy to navigate
        
        No complicated demands
    - - Voice driven interfaces, also called voice recognition, can be used to issue commands to a computer system and enter data into it.
      - Voice-driven interface is a popular interface as it is natural for people to communicate in this way.
      - Benfits
        
        Speech input is much faster than keyboard input
        
        No need to learn to type
        
        Less danger of RSI
        
        Reduces typing mistakes such as spelling/hitting wrong key
        
        Keyboard takes up room on the desk
        
        Users with a disability that prevents typing can use speech input
        
        Hands-free advantages – can multitask
        
        Users find talking more natural than typing.
      - Drawbacks
        
        Background noise interferes with speech recognition
        
        User when they have a speech impediment, sore throat, cold or a strong accent will not be understood
        
        Users with a disability that prevents speech would need to find a different method for input
        
        Difficult to keep data input private as people can hear what you are saying
        
        Words that sound the same, such as ‘too’ and ‘two’ may not be recognised
    - - used to describe the communication between people and computer systems.
      - To allow a person and a computer system to communicate, an interface is required, often called a human-computer interface.
      - Different interfaces are provided by the operating system and can be identified by the style of communication they use.
    - - A Command Line Interface is an entirely text-based interface that allows a user to communicate with a computer system by typing in commands.
      - Before GUIs were developed, command line interfaces were the most widely used interface.
      - Benefits
        
        Quicker to type commands
        
        Quicker to input commands as shortcut keys can be used
        
        Little memory and processing power needed compared with other interfaces
        
        Little storage space is required (no graphical images to store)
        
        Experts who have memorised the commands find it very fast to use
      - Drawbacks
        
        Very confusing for someone who has never used a command line interface
        
        Commands have to be typed precisely. If there is a spelling error the command will fail
        
        Instructions cannot be guessed
        
        Not suitable for a novice
        
        A large number of commands need to be learned
    - - Touch sensitive interfaces are becoming more popular and are extensively used in mobile computing devices.
      - Commands are issued or data is input by touching the screen with your finger or a stylus pen. As well as tapping the touch-sensitive screen, the screen can interpret other actions made by the user, such as pinching and swiping.
      - Benefits
        
        Very intuitive
        
        Easier to use as the user simply touches what is seen on the display
        
        No keyboard or mouse is required
        
        Touching a visual display of choices requires little thinking and is a form of direct manipulation that is easy to learn
        
        Easier hand-eye coordination than mice or keyboards
      - Drawbacks
        
        Screen can be easily damaged/scratched
        
        Dirty screens are difficult to read
        
        Users must be within arm’s reach of the display
        
        It is difficult to select small items
        
        User's hand may obscure the screen
        
        Screens need to be installed at a lower position and tilted to reduce arm fatigue
        
        Some reduction in image brightness may occur
    - - This type of interface allows people to interact with a computer system by presenting the user and allowing them to work through a series of menus.
      - The iPod Classic is a perfect example of a device that uses a menu driven interface as users are presented with a menu that contains a list of artists.
        
        Having chosen an artist, another menu appears with a list of albums belonging to that artist. Following this, another menu is presented with a list of songs belonging to the chosen album.
      - Benefits
        
        No need to learn a lot of commands
        
        Intuitive/easy to understand
        
        Easy to navigate
        
        Ideal for beginners – everything is in a logical place/order
        
        No need of expert language to learn
        
        Little processing power needed
      - Drwbacks
        
        Irritating if there are too many menu screens to work through
        
        Navigating can be a long process
        
        users get annoyed or bored if it takes too long
- - - - A compiler is used when high-level programming languages are converted into machine code, ready to be executed by the CPU. There are four main stages of compilation:
      - Lexical analysis
      - • Comments and unneeded spaces are removed.
      - • Keywords, constants and identifiers are replaced by 'tokens'.
      - • A symbol table is created which holds the addresses of variables, labels and subroutines.
      - Syntax analysis
      - • Tokens are checked to see if they match the spelling and grammar expected, using standard language definitions. This is done by parsing each token to determine if it uses the correct syntax for the programming language.
      - • If syntax errors are found, error messages are produced.
      - • Variables are checked to ensure that they have been properly declared and used.
      - • Variables are checked to ensure that they are of the correct data type, e.g. real values are not being assigned to integers.
      - • Operations are checked to ensure that they are legal for the type of variable being used, e.g. you would not try to store the result of a division operation as an integer.
      - Code generation
      - • Machine code is generated.
      - • Code optimisation may be employed to make it more efficient/faster/less resource intense.