Operating systems

• Memory management

  Moves data from secondary storage to RAM.
• Peripheral management

  Sends data to the output devices.
• File management

  Allows the user to create, name and delete folders.
• User interface

  Allows the user to communicate with the device.
• Data is transferred between devices and the processor. This process needs to be manage.
• There are three types of interface to be considered:

  • graphical user interface (GUI) - sometimes known as WIMP (Windows, Icons, Menus, Pointers) interface
  • mobile user interface (Mobile UI)
  • command line interface (CLI)
• A graphical user interface is familiar to most users of PCs and laptops. GUIs feature a desktop where everything is displayed. Applications run in Windows, and all objects (apps, hardware and files) are represented by icons. Application features are accessible through the use of menus. Users interact with the interface by using a mouse and on-screen pointer.
• Mobile UIs are similar in many ways to GUIs, except that they respond to touch. Fingers are used to open programs and interact with them. Gestures such as swiping are used to scroll within documents. Pinching and stretching are used to re-size images.
• Where are Mobile UIs found?

  • smartphones
  • tablets
• Command line interfaces are text-based. Users control the computer by typing in commands.

  CLIs require little processing power and are extremely powerful, but are difficult to use. Originally most interfaces were CLIs, and they still exist within modern operating systems, for example the command prompt app in Windows, and Terminal in OS X.
• What are some user management functions?

  • Allocation of an account- different users are each provided with an account with their own user name and password
  • Access rights- each user can be granted different levels of access depending on their needs and level of security
  • Security- the OS can monitor login activity and log out users after set periods of inactivity
• What are some key features of file management?

  • Naming
  • Allocating to folders
  • Moving files
  • Saving
  • Access rights to individual files
• Peripheral Management and Drivers

  Peripheral devices connected externally to the CPU include printers, keyboards and monitors. Users must communicate with devices via the OS. A buffer is used to compensate for the difference in speed between the CPU and the device.
• How can an operating system operate a peripheral?

  To operate a peripheral, the operating system uses a program called a device driver. Device drivers contain instructions on how to control a device. Each connected device has its own driver.
• What are advantages of using a device driver?

  • 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
• Memory management and multitasking

  Files and programs need to be in memory for the CPU to perform tasks on them. The OS moves programs and files in and out of memory (from the hard drive or from virtual memory) to process tasks required. Switching quickly between tasks is known as multi-tasking.
• Memory management: What is paging?

  • Memory is broken up into fixed-size blocks, known as pages.
  • Different operating systems allocate their own size to pages.
  • When a program is run, it is loaded into memory. The operating system determines how much memory the program requires, and allocates enough pages to hold it and its documents.
  • 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. The operating system knows what each page occupies and fetches the data held in them when needed.