OS + US

• Operating system


  A group of programs that is essential for managing the computer's resources
• Common examples of operating systems

  • Windows
  • MacOS
  • IOS
  • Linux
• Major functions of an Operating System (OS)

  • User interface
  • Peripheral management and drivers
  • File management
  • Memory management and multitasking
  • User management
• User interface


  • Provides a means of interacting with the computer, often through buttons, keyboards or mice
  • May be purely text using a command line interface, menu driver, or a Graphical User Interface (GUI) /WIMP interface e.g. Windows
• Peripheral management and drivers

  • Allows users to communicate with peripheral devices connected externally to the CPU
  • Uses a buffer to compensate for the difference in speed between the CPU and the device
• File management


  • Allows users to create, delete, move, save and copy files, or allocate them to folders
  • Can search for files, restore deleted files, free up space for new files and prevent conflicts when two users attempt to modify the same file at once
  • Can manage access rights to individual files
• Memory management and multitasking


  • Moves programs and files in and out of memory (from the hard drive or from virtual memory) to process tasks as required
  • Switching quickly between tasks is known as multi-tasking
• User management


  • Provides different users with their own user name and password
  • Can grant different levels of access depending on user needs and security levels
  • Can monitor login activity and log out users after set periods of inactivity
• Utility programs


  • Small programs used in conjunction with the main operating system to manage extra features or functions
  • Not essential to the running of a computer but make specific tasks easier or add an additional layer of housekeeping
• Three common examples of utility programs

  • Defragmentation software
  • Encryption software
  • Data compression software
• Defragmentation software


  1. Files are stored on the hard disk in blocks

  2. As different sized files are added and deleted over time, gaps appear which may not fit all of the next file to be stored

  3. Files become fragmented in order to fit them in

  4. Defragmentation moves everything around to avoid fragmented files

  5. Speeds up the computer's file retrieval and storage times
• Encryption software


  • Used to encrypt or decrypt files or folders held on a computer, transmitted across a network or when they are transferred to external devices
  • The encryption process uses an algorithm and a key to transform plaintext into ciphertext
  • To decode the original information, it would be necessary to know both the algorithm and the key
• Data compression software


  • Uses an algorithm to resave the data in an existing file using less space than the original
  • Sometimes data is lost (lossy compression) and in other times, the file can still be reconstructed without any loss of information (lossless compression)
• Command-line interface


  • Users type commands to communicate with the OS
  • Begins with a prompt, such as C:\>
  • Commonly used sequences of commands are often batched together in scripts so multiple actions can be initiated using single commands
  • Can be an efficient way of communicating with the OS as long as the user knows the commands
• Graphical User Interface (GUI)


  • Enables users to interact with the OS through windows, icons, menus and pointers
  • Intuitive and reduces the need for users to learn complex commands
  • Requires more RAM and processing power
• Other user interfaces


  • Menu driven interfaces
  • Voice input interfaces
• File extensions


  Help operating systems determine file types and which applications to use when opening these files
• The operating system also...

  • Monitors performance and alerts the user to problems
  • Operates utilities to maintain the computer and enable applications to run smoothly
  • Runs virus protection and diagnostic software