Operating Systems

Operating Systems

1. Managing Resources

   • Peripherals
     • A peripheral is a device that is attached to the computer, such as a webcam or memory stick
     • Operating systems require driver software for each device
     • A device driver maps the operating system’s commands to the device’s commands
     • For example, it contains the specific machine code needed to print a specific character on that brand of printer.
   • Printing
     • If my program needs to print a document, I tell the operating system to print it.
     • The operating system will then spool the print job (it will keep it in a queue until the printer is ready)
     • This means my program doesn’t need to worry if the printer is busy or unplugged or out of ink.
   • Backing stores
     • Backing stores are storage devices used to keep backups of important files
     • Operating systems can often manage this for the user
     • The OS will make regular backups in the right format an appropriate device (Cloud, Tape or Disk)
   • File compression
     • File compression is storing data in a way that keeps the same information but uses less disk space.
     • The same information is stored, but the second way uses fewer bytes.
     • Operating systems can compress data as it’s saved and decompress it as it’s loaded, allowing more data to be stored on a device.
   • Disk De-fragmentation
     • Disk defragmentation involves re-arranging file fragments on a physical disk surface to improve load times
     • This will be looked at in greater detail in the Utility Software lesson.
   • Memory (RAM)
     • In order to ensure there is enough memory for each program that is running, Ram is split into “pages”
     • Each page is presented to its program as if it is the only memory the system has.
     • This prevents programs from snooping on data from other programs.
   • Processes (Multi-tasking)
     • Modern processors can execute 4 billion instructions every second.
     • This is more than memory and secondary storage can keep up with
     • While a processor waits for other components to catch up, it is not doing anything
   • Security

2. Interface

   • GUI (Graphical User Interface)
     • A GUI is used by most PC and phone operating systems.
     • Graphical representations of the computer’s functions are shown to the user and controlled by touchscreen or a mouse and keyboard.
     • Programs often run in windows and several can be shown at the same time.
   • CLI (Command Line Interface)
     • A CLI is a text-based interface.
     • The user types commands, and the result is shown as text.
     • Nearly every operating system provides a CLI.
     • These are harder to use, but are very lightweight and robust – they use few system resources and are very unlikely to crash or break
   • File management
     • Copy files
     • Move files
     • Delete files
     • Sort files
     • Search for files
   • System settings
     • Operating systems enable the user to easily alter system settings.
     • Settings include
       • Enabling or disabling specific hardware
       • Changing the volume
       • Adjusting screen resolution
       • Configuring secondary storage
   • Multi-Tasking
     • Multitasking is allowing multiple processes appear to run simultaneously.
     • CPUs don’t generally support this, so the OS simulates it by alternating which processes get CPU time.
     • A GUI will generally allow different processes to run in separate windows, and be displayed side by side.
   • Error messages and support
     • When something goes wrong in a program, the user needs to be informed.
     • However, the programmer may not know how the program is being used (GUI, CLI or remotely on an embedded system).
     • The error is passed to the operating system, which then displays it in the most suitable way.
     • This produces consistent error handling regardless of what application is being used.
   • Customisation options
     • The ability to customise the interface is a feature of most operating systems.
     • Some provide options to change the colour scheme and desktop background
     • Others allow a completely different desktop environment to be installed.
   • Task management
     • Operating systems manage processes and allow multitasking.
     • The also provide the user with the option to quit programs, or kill unresponsive processes.
     • Some also allow the user to prioritise certain processes, allowing certain apps to use the full processor speed.