Operating system

• What does interface mean


  Communication
• What is the operating system


  Provides the interface between the user and the hardware
• Application software

  uses applications such as word or spread sheet for the user to accomplish a given task

  The role of the operating system is to provide a platform on which the application software to run
• User interface


  Application software usually involves a common user interface so the user is interacting With the application software in a familiar friendly way
• How does the user, application, user interface and operating system?


  The application system will have a user and the operating system is providing a platform for those applications to run and it’s providing its own user interface experience in addition to the application software
• Utility software


  Many utility software, some of which are built in the operating system that help maintain the computer
• Utility software examples


  Encryption software and defragmentation software
• Memory management 


  Loading various programs into memory to be executed and managing the data those programs acquire
• File management


  To save what’s in the memory to not loose your work when the power is turned off. Manage file store and makes decisions about where files going to be Loaded from
• Device driver


  To translate operation system into something that the hardware is actually going to understand
• Interrupt handling


  This is when any device requires the attention of the processor
• Examples of interrupts 


  Power failure or a user pressing a key on the keyboard
• Multi-tasking


  When you have more than one program open and running at the same time. The processor is allocates a small amount to each process and cycles between them. As this happens very quickly, it appears multiple programs are working simultaneously.
• File management 


  Data is stored in files. An extension to the file name tells operating system which application to load the file like example.docx. The OS may present a logical structure of files in folders and allow the user to rename, delete, copy and move files.
• User management 


  Allows multiple users to log into the same computer. The OS will retain settings for each user such as icons, desktop backgrounds, etc
• User management Example


  A client server network may impose a fixed or roaming profile for a user and manage login requests to the network.
• USER interface examples


  WIMP= windows, icons, menus and pointers
• 2 strategies for memory management

  Paging and segmentations
• Paging 


  Programs are split up to fit into a given number of pages. Paging takes into no account of how it splits it into fixed-sized pages. It could separate the instructions inside a looping conditions so they are in different pages.
• Pages


  Pages are fixed size. Pages are made to fit sections of memory. Pages are physical divisions .
• Segmentations 


  The segments are different sizes. Segmentations are complete sections of programs. Segments are logical divisions.
• Similarities in paging and segmentations


  Both allow programs to run despite insufficient memory

  Pages and segments are stored on disk

  Pages and segments are transferred into memory when needed.
• Difference in paging and segmentations 


  Pages are fixed sizes, Segments are different sizes

  Pages are made of fit sections of memory, segments are complete sections of memory

  Pages are physical divisions, segments are logical divisions.
• What happens if if the size of the programs being executed is larger than the RAM available?


  There is significantly more room available on the hard disk. If physical memory is low, virtual memory must be used.
• Negative affects of using virtual memory?


  If more time is spent to move pages/segments from memory to the disk (thrashing) than processing instructions, the computer is very slow.