Operating Systems

• Examples of operating systems:

  • MacOS.
  • Windows 10, Windows 11.
  • iOS.
  • iPadOS.
  • Android (based on Linux).
  • Linux.
  • Chrome OS.
• An operating system is responsible for managing the hardware and software in a computer.
• The user interface allows the user to tell the computer what to do. It also shows the results after processing.
• Types of user interface:

  • GUI: Graphical User Interface.
  • Menu-driven interface.
  • CLI: Command Line Interface.
  • Voice activated.
  • Real-time.
• Windows makes use of a WIMP user interface. It uses Windows, Icons, Menus and Pointers.
• WIMP interfaces:

  • Windows are used to show each different program that is currently open.
  • The user can click on icons using a pointer or cursor.
  • Icons represent key functions and are used to launch programs.
  • Menus are used within programs and also as context-sensitive menus when you right-click.
  • Different shaped pointers indicate the current function of the pointer or state of the computer.
• Menu-driven interfaces make use of menus where the user selects options that lead to further sub-menus

  • Some music players still make use of menus.
  • Menus are often used for settings on televisions.
• Command line interfaces are also known as text-based user interfaces.
• Command line interfaces:

  • Allow the user to enter commands by typing.
  • Only text is displayed.
  • Command line interfaces are faster to use for some tasks if the user knows how to use them.
  • They take less disk space and RAM.
• When you open a program the operating system loads the program into RAM.
• The operating system provides a platform for each program that is running on the computer.
• The operating system deals with where the program and data go in the memory (memory management), the saving of files and how much time each program has to use the CPU (task management).
• Software is released for a particular operating system as well as a particular computer architecture.
• To run a program, the computer must copy each program (and data used by the program) from storage into main memory.
• The operating system keeps a record of where each program and its data are located.
• The operating system makes sure that programs don't overwrite existing programs.
• Multi-tasking is when people use their computer to run several programs at the same time.
• Multi-tasking.

  Each program is given a short time on the CPU before it is paused by the operating system. The operating system then allows the next program to make use of the CPU for a short time. By switching quickly between different programs (tasks), its appears to the user that all of them are happening at the same time.
• Examples of peripheral devices:

  • Digital cameras and webcams.
  • Graphics tablets.
  • Microphones.
  • Solid state media (USB sticks and SD cards).
  • Magnetic tape drives.
  • Bar code reader.
  • RFID reader.
  • Optical drives (CD, Blu-Ray and DVD drives).
• Each peripheral device requires a device driver to operate.
• The device driver allows the operating system (and programs) to access the device.
• The device driver must be installed before the peripheral device may be used.
• Device drivers are written in assembly language or a language that can access low level instructions. This is because they have to precisely control the hardware devices.
• Operating systems contain a file system.

  • This allows both users and programs the ability to copy, save and rename files.
  • Files may be placed in a folder.
  • Saving files is often a complicated process, but for the programmer it is easy as they just ask the operating system to do it.
• Folders are also known as directories in text-based systems.
• The operating system must manage the following:

  • Which platter to save to.
  • Which track to send the drive head to.
  • Which sector needs to be accessed.
  • Make sure that files don't overwrite existing ones.
• The operating system is responsible for the security of the computer system.
• Managing security with operating systems:

  • Authorised users are checked with a username and password combination, PIN or facial recognition.
  • Access to certain programs may be restricted.
  • Individual files may be protected.
  • Other rights may be restricted, such as the ability to install software.
• Access rights:

  • If a computer is used by more than one person, users need to be restricted as to which files they may see.
  • A user may be given access to just the files they have made, whilst a system administrator may have access to all files.
  • Some users may be allowed to read files but not edit them.
• An operating system's functions:

  • Managing files.
  • Managing peripherals and drivers.
  • Managing memory.
  • Managing multitasking.
  • Managing user accounts.
  • Providing an interface.
  • Providing a platform for running applications.
  • Providing system security.
• A driver is software used to provide an interface for a hardware device.
• Peripherals are external hardware devices that connect to a computer to add functionality.