3.1 - The Function of Operating Systems

3.1 - The Function of Operating Systems

1. The main features of operating systems

   • An OS must:
     • Provide and manage hardware resources
     • Provide an interface between the user and the machine
     • Provide an interface between applications software and the machine
     • Provide security for the data on the system
     • Provide utility software to allow maintenance to be done
   • Original purpose was to prevent duplication of code by providing input and output resources
     • Prevents each individual program from having code to control input and output (duplication of code)
     • Input-Output Control System (IOCS)
   • Development of assembly/high level languages means that OS needed:
     • A translator program to turn human friendly code into computer friendly code
       • Assembler - Handles translation from assembly language
       • Compiler - Translates high level code into object code
       • Interpreter - Translates a line of high level code and runs the result before translating the next line
   • Memory management
     • More than one program should be stored in memory and the processor should give time to each of the programs
       • Processor should give time to each of the programs and process higher priority processes first of all
     • OS needs to keep all programs separate along with any data they use
     • Spooling
       • Memory used to store data that has been inputted by user or that is about to be outputted until the processor deals with it
     • Loader
       • Remembers memory locations of each instruction or each piece of data

2. How Interrupts are Used to Obtain Processor Time and how Processing of Interrupted Jobs may Later be Resumes