GCSE computer science

• Operating system


  The software that manages the hardware and software resources in a computer system
• Operating systems


  • Controlling hardware components
  • Providing a platform for software to run on
  • Providing a user interface
  • Providing multitasking facilities
  • Managing the computer's memory
  • Managing peripherals
  • Managing files
  • Managing users
• User interface


  The means by which a user interacts with a computer or device
• Types of user interface


  • Graphical user interface (GUI)
  • Mobile user interface (Mobile UI)
  • Command line interface (CLI)
• Graphical user interface (GUI)


  • Familiar to most PC and laptop users
  • Features a desktop where everything is displayed
  • Applications run in Windows
  • Objects (apps, hardware, files) represented by icons
  • Application features accessible through menus
  • Users interact using a mouse and on-screen pointer
  • Powerful and easy to use, but requires a lot of processing power
• Mobile user interface (Mobile UI)


  • Similar to GUIs, but responds to touch
  • Fingers used to open programs and interact
  • Gestures like swiping, pinching, and stretching used
  • Found on smartphones and tablets
• Command line interface (CLI)


  • Text-based
  • Users control the computer by typing in commands
  • Require little processing power
  • Extremely powerful, but difficult to use
  • Originally most interfaces were CLIs, still exist within modern operating systems
• Systems software


  The programs, applications and data in a computer system. Any parts of a computer system that aren't physical.
• Systems software


  • Controls the hardware
  • Allows other programs (applications) to run
  • Provides an interface for the user to interact with the computer
  • Maintains the system
• Operating systems


  The software that manages the hardware and software resources in a computer system.
• Utilities


  Programs which perform important maintenance tasks to improve the performance of a computer system.
• Multitasking


  Ability to run more than one program simultaneously
• In the past, computers with CLIs were unable to multitask - the operating systems of the day only allowed one program to run at a time
• Modern operating systems are multitasking in that they allow several programs to run side-by-side
• It is not uncommon for a user to be streaming music while entering text into a word processor, or streaming a video while making a backup of files
• Multitasking is possible only if


  • The operating system can support multitasking
  • The computer has enough memory to hold more than one program in primary memory at the same time
• Paging


  A method of memory management where memory is divided into pages
• Memory is broken up into fixed-size blocks, known as pages
• Different operating systems allocate their own size to pages, typically 4 kilobytes (KB) in size in modern operating systems
• When a program is run


  1. The operating system determines how much memory the program requires

  2. Allocates enough pages to hold it and its documents

  3. When the program is closed, the allocated pages are freed up for use by other programs
• The pages a program occupies may or may not be contiguous, but this does not matter as the operating system knows what each page occupies and fetches the data held in them when needed
• Peripherals


  Hardware devices connected to a computer, such as a monitor, printer, scanner or camera
• Device drivers


  Programs that control and communicate with peripherals
• Using device drivers brings two advantages


  • Any device can be used with the operating system, as long as a driver is available for it
  • Drivers can be updated, usually to give better performance or to remove a bug
• File handling and file maintenance


  1. Create, modify and delete files and folders

  2. Copy and duplicate files and folders

  3. Move files and folders

  4. Rename files and folders

  5. Sort items into different orders, according to name, file type, date created and more

  6. Search for particular files and folders

  7. Restore deleted files

  8. Set access rights to files such as read only or edit
• User management


  • Allows individual users to be created and deleted
  • Gives access levels to users, such as administrator rights or standard user rights
  • Audits (keeps a log of) files a user creates, accesses, edits and deletes
• Systems software


  The programs, applications and data in a computer system. Any parts of a computer system that aren't physical.
• Utility software


  Software that helps maintain the system
• Utility software includes


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


  Software that disguises the contents of files so they can only be understood by authorised users
• Algorithm


  A sequence of logical instructions for carrying out a task. In computing, algorithms are needed to design computer programs.
• Fragmentation


  When a file is stored on a hard disk, it is actually stored not as a whole file, but as a series of segments. Sometimes the segments run together in sequence and sometimes the segments are split up over a disk.
• Defragmentation software


  • Takes the fragmented files and rearranges the segments so that they run contiguously, decreasing read/write time and speeding up computer performance
• Data compression


  A method of reducing file sizes, particularly in digital media such as photos, audio and video
• Backup


  A copy of important files that is kept separately in case the original files are lost or damaged
• Types of backup


  • Full backup
  • Incremental backup
• Full backup


  A copy of every file on the computer or network
• Incremental backup


  A copy of any new files created since the last backup, or of any files that have been edited