1.2.1 Systems Software

• Basic Input Output System (BIOS)

  • a program that initialises and tests whether system hardware is functional and then loads the OS from the hard disk to the RAM when the computer turns on
• Device Drivers

  • program supplied with a peripheral device allowing the OS to control and communicate with the device
• Distributed Operating Systems

  • OS is spread over multiple computer servers on a network, acting as a single system to parallel process the job
• Embedded OS

  • a specialised OS with limited resources and functionality, built in to control a single machine
• First Come First Served (FCFS)

  • scheduling algorithm where processes are dealt with in the order they arrive (queue)
• Intermediate Code

  • code partly translated between high-level and machine language produced by a compiler
• Interrupts

  • a signal from hardware, software or the clock to alert the CPU
  • if the interrupt is higher priority than current task, current routine pauses and resumes after interrupt is executed
• Interrupt Service Routine (ISR)

  • if an interrupt is high priority than current task, register contents transfer temporarily onto the system stack at the end of the current FDE cycle and the interrupt is handled
• Memory Management

  • efficient organisation and allocation of main memory to the programs in use
• Multi-Level Feedback Queues

  • a scheduling algorithm that uses multiple queues, each with a different priority
  • jobs can be moved between queues
• Multi-tasking OS

  • an OS capable of running multiple tasks simultaneously
• Multi-User OS

  • an OS consisting of one mainframe computer with multiple terminals
  • this lets multiple users access computer's resources
  • each user is given a time slice of the mainframe processor
• Operating System (OS)

  • a set of programs managing the operation of the computer that's loaded into RAM everytime the computer is turned on
  • bridges user to hardware
• Paging

  • separating memory into fixed sixed physical divisions called pages
  • processes in memory will be assigned an appropriate number of pages
• Real Time OS

  • an OS where data is processed as it comes
  • responses are generated within a guaranteed timeframe
• Round Robin

  • scheduling algorithm where each process is given an equal time slice and dealt with in a First In First Out basis
  • if a process doesn't finish within a time slice, it joins the end of the queue
• Scheduling

  • allocating processor time to each application to make sure processor time is used efficiently when multitasking
• Segmentation

  • separating memory into variable sized logical divisions called segments
  • a large program can be executed by consecutively running its segements
• Shortest Job First

  • scheduling algorithm that picks the process with the shortest estimated running time and runs it till it's finished
• Shortest Remaining Time

  • scheduling algorithm that picks the process with the shortest estimated time remaining
  • if a process with a shorter time is added, scheduler switches processes
• Virtual Machines

  • any instance where software is used to take on the function of a machine
  • includes intermediate code/running an OS in another
• Virtual Memory

  • an allocated area of secondary storage where pages of inactive jobs are swapped into to free up RAM for the current job