computer science revision - 3

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  • software
    • software is the term given to the programs that we run on our computers
      • software also refers to the data that is used by the programs
    • dedicated systems have software downloaded on a chip, this software is specific to the job and is only changed when updated.
    • Multi-purpose computers such as laptops, tablet computers etc. regularly run different programs according to the desires of the user
      • multi purpose computers store their software on a secondary storage medium such as:
        • a hard disk, memory stick, SD card or optical disk
    • system software controls the hardware
    • application software handles the 'real-world' jobs that the user wants to do
    • utility software has limited functionality and is used to maintain computer systems
    • system software
      • controls the hardware
      • hides the complexities of the hardware from the user
      • allows the user to operate the computer without having to write programs
      • the main part of system software is the operating system
    • user interface software
      • an operating system must provide a way for a user to control and interact with a computer
      • the user interface is the boundary between the human and user and the machine
      • the interface: lets the user give commands, ask questions and displays a response
      • graphical user interface (GUI)
        • uses images, known as icons to represent resources, files, programs and actions.
        • useful because they are: intuitive, no special training is needed, keyboard use is limited and no commands need to be learnt
        • this interface sits on top of the operating system kernel and allows easy access to many of its everyday features, such as:
          • selecting software, selecting files, sending messages
      • natural language and speech
        • some interfaces accept normal speech as input
          • difficult to get right as speech can vary according to:
            • accent, speed of talking, dialect, clarity
        • speech input can be useful for selecting options on telephone menus, giving commands to computers or dictating text.
    • memory management
      • operating systems have to decide what goes where in memory, they have to make sure that:
        • memory is used efficiently
        • important data is not over written during the running of a program
          • to do this, memory is divided into pages
      • virtual memory
        • sometimes there are more jobs than the memory can hold. the operating system then swaps jobs in and out of memory using a technique called virtual memory
        • virtual memory means 'not real' memory
        • a large program may take up too much memory so it is divided into modules
          • the modules are stored separately on secondary storage
          • when a module is needed it is loaded into memory and runs as a process
          • when a different module is needed it can overwrite an unused module
      • peripheral management
        • a file is a named store of data on a secondary storage medium
          • files can be:
            • data files: such as a word processed document or a database
            • program files: such as operating system components or applications
            • configuration data: such as the parts of the windows registry
      • fragmentation and de - fragmentation
        • secondary storage is divided into segments
          • then files are split into blocks within these segments
        • de - fragmentation is the process which tidies up the disk or other medium so that the parts of the files are moved to be stored next to each other
      • multitasking
        • a multitasking operating system must:
          • make sure that the CPU is in as much use as possible
          • try to speed up the operation of all tasks
          • share resources fairly between tasks
        • when there are multiple processes running at the same time, the operating system uses a scheduler in order to allocate time.
          • this allocation of time is made according to a policy
            • for example:
              • first come first served
              • shortest job first
              • all jobs get equal timing
              • priorities
    • programming software
      • editors
        • they allow text files to be:
          • created
          • saved
          • read
          • changed
      • linkers
        • these combine modules of object code into a single executable program
      • interpreters
        • convert typed commands into the machine instructions that the processor understands
    • applications and utilities
      • applications are the programs that people use to do 'real-world' jobs such as
        • word processors
        • traffic light controls
        • games
        • bar code readers
      • utilities are software tools that help make maintaining the system easier
        • for example
          • antivirus software detect and remove viruses
          • spyware protection
          • firewalls monitor traffic entering and leaving a system
      • system maintenance utilities help you clear away any redundant files
      • system information and diagnosis utilities check fir problems on secondary storage
      • system clean up tools search for un used files and clear them out
      • automatic updating utilities check for online updates at intervals
    • software procurement
      • system managers must make choices so that their organisation gets systems:
        • as required
        • on time
        • at a reasonable cost
      • custom written software
        • specially commissioned for a particular customer
        • ADVANTAGES
          • It should have the exact features required
          • not require special adaptations to be made after installation.
          • the developer can be contacted to solve issues
          • the developer may provide training
        • DIS ADVANTAGES
          • may not have been extensively tested
          • expensive
          • long time to develop
      • off the shelf software
        • bought from supplier, ready to install
        • examples include: Microsoft office, windows, Norton security software
        • ADVANTAGES
          • ready immediately
          • extensively tested
        • DIS ADVANTAGES
          • probably not exactly what the customer needs
          • search for trainers
      • open source software
        • placed in the public domain by the programmers
        • examples: firefox, linux
        • ADVANTAGES
          • free of charge
          • can be altered
          • extremely reliable
        • DIS ADVANTAGES
          • no maintenance contracts
          • no one to contact if there are any problems
          • updates aren't regular
      • proprietary software
        • developed for a profit by a company
        • ADVANTAGES
          • someone to contact if there's any problems
          • extensively tested
          • updates regular
        • DIS ADVANTAGES
          • can be expensive
          • deliberate in in compatibilities so users can be locked in
          • inflexible to users needs

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