Operating systems

• interupt is called when a process needs attention
• Interrupts can be interrupted by other interupts

  When this happens the content in the registers from the previous interrupt are added to the stack ontop of the prevo interrupted process
• Paging makes pages or also called physical divisions
• Segmentation is split into segments or also called logical divisions
• Paging makes the pages the same sizes and are used to fit the program in the spaces it has in memory
• Segmentation splits programs into different sized divisions based on logical divisions
• Virtual memory is stored in the hard disk
• Bios , the basic input output system,loads the operating system into ram when pc is turned on
• The BOIS checks all hardware is connected and working in the POST or power on self tests
• the bootstrap loads the operating systems kernel into memory
• BOIS instructions are in flash memory
• initial start up instructions are in ROM
• device drivers are software that tells the operating system how to communicate with a particular device

  device drivers translate the operating systems instructions so specific piece of hardware will understand
• types of operating systems

  • distributed
  • multitask system
  • multi user,multi tasking system
  • operating systems for phones
  • embedded
  • real time
• distributed operating systems - forms of parallel processing system which spreads the load over multiple servers

  eg. windows
• multitasking system - may run on standalone

  the operating system runs jobs simultaneously by flicking between jobs extremely fast
• operating systems for mobile phones

  they are tied to specific hardware

  smart phones have two operating systems

  1 is for the user interface e and application software and the 2nd one is for low level, proprietary - real time system.
• embedded operating system

  • minimal user interface
  • accept inputs and sends out outputs
  • limited ram so complex memory management isn’t needed
  • no permeant data storage
• real time operating systems

  • responds very quickly to inputs or sensors
  • deals with many inputs simultaneously
  • has a fail safe if hardware fails
  • must incorporate redundancy - so back up hardware
• virtual machine is the instance where software is used to take on the function of the machine, including intermediate code or running an operating system within another to emulate different hardware
• Why is an operating system necessary for a computer

  It does things such as:

  Resource management which includes things such as memory managements ,peripheral management(input / output )

  To make things more efficient

  It also sits between the hardware and the user

  It shows the interface for hardware software
• paging avoids external fragmentation but causes internal fragmentation
• segmentation leads to external fragmentation
• Virtual memory is a tenique
• an interupt is a signal for a program
• what scheduling algorithm ensures that every process has equal cpu time?

  round robin
• what scheduling algorithm is best suited for minimising the average waiting time?

  shortest job first
• key characteristics of realtime operating system

  immidiate and in a garenteed time-frame
• how can a virtual machine be used to run an operating system within another operating system?

  as it emulates hardware