Functions of an Operating System

Functions of an Operating System

1. all OS's share the same basic functions

   • disguises the complexities of managing and communicating with hardware from the user
     • via an Application programming Interface (API)

2. Memory management

   • = the allocation and management of space
   • Each program, open file, etc. has to be allocated a specific area of memory
     • each application must be stored in memory simultaneously
   • What if computer's RAM is not large enough to store all programs simultaneously?
     • hard disk used as an extension of memory
       • virtual memory
         • e.g. MS Word software and data may be copied to hard disk to free up RAM for e.g. browser software. When you switch back to word, OS reloads it

3. processor scheduling

   • = allocating processor time to each application as they compete for the CPU
   • multi-tasking
     • can be done by a computer with a single-core processor
     • carrying out small parts of multiple larger tasks in turn
       • gives the appearance of carrying out multiple tasks simultaneously
   • scheduler (operating system module)
     • responsible for making sure that processor time is used as efficiently as possible
     • maximise throughput
       • throughput = a measure of how many units of information a system can process in a given amount of time
     • fair to all users on a multi-user system
     • provide accpetable response time to all users
     • ensure hardware resources are kept as busy as possible

4. backing store management

   • loading files/apps = transferring them from backing store to memory
   • OS needs directory of where files are stored
   • which areas of storage are free?
     • so new files or applications can be stored
   • file management system in OS
     • enables user to move files/folders
     • delete files
     • protect files from unauthorised access

5. management of all input and output (peripheral management)

   • check devices are switched on+online
   • check type of device
   • begin communication to send correct data to devices
   • ensures peripherals are allocated to processes without causing confilicts

6. Interrupt handling

   • interrupt = signal from a peripheral or software program that causes OS to stop processing current list of instructions and think what to do next
     • e.g. software crash or "out of paper" printer message
   • OS detects interrupt signal and displays appropriate error message to user
   • processor can be interrupted allows multi-tasking