hardware and software

• hardware:

  physical parts of the computer system
• software:

  non-physical parts of the computer (instructions/program)
• difference between application and system software:

  application - enables user to complete user-oriented tasks. System - controls the operation of computer system
• Functions provided by the operating system (4):

  memory management, backing store management, processor scheduling, I/O device management
• Purpose of operating system:

  hide the complexities of hardware from the user
• instruction set:

  all the instructions a computer can execute
• difference between immediate and direct addressing:

  immediate - operand is the value to be used. Direct - operand is the memory address containing the data to be used.
• examples of system software:

  libraries; utility programs; operating system
• types of application software (3):

  general purpose, special purpose, bespoke
• Compiler:

  • Checks for errors, then translates whole source code
  • Compiler is not needed when running object code
  • Sometimes produces intermediate code, which is executed by virtual machines. Allows code to be translated and executed on different processors
• Situations where LLL may be used over HLL:

  • where precise timing is needed, e.g device drivers (for synchronisation between devices)
  • where direct control of program function is required
• Describe operation of virtual memory:

  • Using secondary storage as main memory.
  • physical memory is conceptually divided into fixed size pages
  • OS creates set of virtual addresses
  • Data in VM is stored as pages
  • when CPU is ready, page files are swapped into RAM (and data from RAM is moved into VM or secondary storage) by translating virtual - real addresses. If this is done too often, thrashing occurs.
• describe what utilities are:

  software that performs a specific management function for the computer
• describe the role of control unit:

  Controls execution of fetch-execute cycle, determines type of instruction. Controls transfer of data between registers. Sends control signals. Handles interrupts.
• Explain why the final version of a program is usually translated with a compiler:

  Source code cannot be accessed by users

  It will execute faster
• Explain why programs intended to be executed in a web browser would be interpreted rather than compiled:

  Compiled program would only run on a processor with the same instruction set, whereas interpreted program would run on any type of processor, and you don't know what processor the user would have