Operating systems

• What is BIOS used for?

  carrying out checks on core system components

  starts the boot loader
• What does a device driver do?

  translates commands from the OS into hardware specific commands that a device understands
• Define operating system


  Manages the computer processor, memory, peripherals, files, logins and user settings

  Provides a user interface
• What is embedded OS usually designed for?


  specific types of machine/computers
• Functions of an OS

  • Security
  • Utility software
  • Memory management
  • I/O management
  • Interrupt management
• Real time OS

  An operating system intended to serve real-time application data as it comes in without buffering delays
• Define what is meant by scheduling

  The method by which central processor time is allocated to processes
• Why is scheduling necessary?

  • Process as many jobs as possible in least possible time
  • Ensure all jobs are processed
  • Maximise number of interactive users with fast response times
  • Efficient use of resources and processor time
• How does first come first serve work?

  Deals with each user request or task in the order in which they arrive
• Can first come first serve be interrupted?

  It is non pre-emptive, the executing process cannot be stopped once started
• How does round robin work?

  Each process has a given time slice

  After which it returns to the back of the ready queue
• How does shortest job first work?

  The ready queue is sorted in order of estimated processing time before processes begin executing in order
• How does shortest remaining time differ to shortest job first?

  Shortest time remaining is pre-emptive, it can be stopped and added to restarting again
• Define real-time


  The system gives a response within a guaranteed time frame
• What is intermediate code?

  code produced by the compilation process
• What is intermediate code translated by?


  virtual machine or output from compiler
• What is a multi-level feedback queue?

  A scheduling algorithm that deals with processes based on a set of priorities and rules using multiple queues
• What is virtual memory?

  using part of secondary storage as if it were RAM
• Why is memory management necessary?

  • Can organise the use of main memory by converting logical addresses to physical addresses
  • Allows programs to share and allocate memory
  • Allows programs larger than main memory to run
• What is paging?


  The organisation of memory into physical, fixed-sized units, called pages, used for virtual memory
• Where is paging used?


  Used in virtual memory
• What is meant by segmentation?

  Parts of a program divided into unequal sizes, using logical divisions
• Similarities between paging and segmentation?

  • both methods of splitting up memory
  • both use virtual memory
  • both allow programs larger than memory to run
  • both allows programs to be stored in memory non-continuously
• Define device driver


  Software that allows the operating system to communicate with hardware
• Why would a operating system use round robin?

  • To enable multi-tasking
  • To switch between active processes and those running in the background
  • To allow processes an equal share of processor time