Functions of an Operating System

Functions of an Operating System

1. Features

   • Error Reporting
   • Memory Management
   • Resource Management
   • Input/Output Management
   • Device Management
   • Interrupt Management
   • User Interface
   • F.A.T
   • Boot File

2. Interrupts

   • Types
     • Peripheral Interrupt (I/O)
     • Power failure
     • Clock Interrupt
     • Software Interrupt
     • User Interrupt
   • Why have Priorities?
     • Decide between current task or interrupt
     • To choose which to process if 2 occur together
     • To ensure most urgent task processed first
     • Effecient use of processor
   • Why use them?
     • Gain processing time
     • ...for a higher priority task
     • Avoids delays
     • Avoids loss of data

3. Scheduling

   • Methods
     • Round Robin
     • Shortest Job First
     • Shortest Time Remaining
     • First Come First Served
     • Multi-Level Feedback Queue
   • Why use it?
     • Maximise number of jobs processed
     • Process jobs as quickly as possible
     • Effecient use of processor time
     • Ensure all jobs gain some processing time
     • Maximise number of users with no apparent delay
   • Why have Job Priorities?
     • Some jobs more urgent than others
     • Maximise use of resources

4. Memory Management

   • Why is it necessary?
     • Allocates memory to allow seperate process to run simulataneously
     • To reallocate memory when required
     • To protect processes/data from each other
     • To provide data security
   • Virtual Memory
     • Paging & Segmentation
       • Paging
         • Pages fixed in size
         • Pages made to fit sections of memory (equally)
         • Pages are physical divisions
       • Way of partitioning memory
       • Allows programs to run when insufficient memory
       • Pages/segments stored on secondary storage when inactive
       • Pages/segments assigned to memory when needed
       • Segmentation
         • Each job has a whole segment
         • Segments are logical divisions
         • Segments can vary in size
     • Allows programs to run that require more memory than available
     • Holds part of program not in use in secondary storage
     • Programs using this run slower
     • Disk threshing problem may occur

5. Spooling