Chapter 7 - Functions of an operating system

Question 1

What are some functions of the operating system?

Answer 1

» Hardware
» User interface
» Memory management
» File management
» Multitasking
» Scheduling

Question 2

What is a helpful acronym to remember the functions of the operating system?

Answer 2

» MUSH FM

Question 3

What is multitasking?

2 marks

Answer 3

» When you have more than one program open and running at the same time
» Processor allocates a small amount of time to each process and cycles between them

Question 4

What is user management?

Answer 4

» Allows multiple users to log into the same computer
» OS will retain settings for each use

Question 5

What is WIMP?

Answer 5

» Windows
» Icon
» Menus
» Pointers

Question 6

What is an operating system?

Answer 6

» A collection of programs that work together to provide an interface between the user and the computer
» Manages the computer’s hardware

Question 7

What is the user interface?

Answer 7

» The means by which the computer and user interact
» Can be a commmand line interface
» Can be a GUI interface

Question 8

Where is the OS held?

Answer 8

» On the hard disk

Question 9

How does is the OS loaded into RAM?

Answer 9

» Small program called loader which is in ROM sends instructions to load operating system by copying it from storage into RAM

Question 10

Why is memory management needed?

2 marks

Answer 10

» Protects programs from each other, such as being overwritten
» To enable memory to be shared
» To rellocate memory when necessary

Question 11

How does the operating system manage memory management?

Answer 11

» Memory is used efficently - program that are being used need to be stored in memory without space being wasted

Question 12

What are the 2 ways in which memory can be split?

Answer 12

» Paging
» Segmentation

Question 13

What is paging?

3 marks

Answer 13

» Memory is split into equal-sized sections known as pages
» Can be swapped between main memory and the hard disk as needed
» Pages are physical divison that are made to fit sections of memory

Question 14

What is segmentation?

3 marks

Answer 14

» Splitting up of memory into logical sized divisions known as segments
» Segments are different sizes
» Segments are complete sections of programs

Question 15

When is virtual memory needed?

Answer 15

» When there is insufficient memory space in RAM to store prgorams

Question 16

Which is more expensive, RAM or secondary storage?

Answer 16

» RAM

Question 17

How does virtual memory work?

Answer 17

» Uses a section of the hard drive to act as RAM
» Sections of program that are not currently in use are temporarily moved into virtual memory through paging.
» Pages are swapped to main memory when required

Question 18

What is disk thrashing?

Answer 18

» When the computer slows down
» Due to pages being swapped too frequently between the hard disk and main memory
» As a result more time is spent transferring these pages, then actually running the program

Question 19

What is an interrupt?

Answer 19

» Signals generated by software or hardware to indicate to the processor that a process needs attention

Question 20

What is the interrupt Service routine?

Answer 20

» Program code that is called when an interrupt is called
» Checks to see the priority of the interrupt

Question 21

What is a priority queue?

Answer 21

» Stores the interrupts in order of their priority

Question 22

When does the processor check the contents of the interrupt?

Answer 22

» At the end of each FDE cycle

Question 23

What are the steps of the ISR when the priority is higher priority then the process being executed?

Answer 23

» Contents of the program counter and other special purpose registers are copied transferred to a stack
» Relevant ISR can be loaded by changing the program counter to the locaiton of the ISR in memory
» When ISR is complete, previous values of the program counter and other registers can be restored by popping the stack

Question 24

What happens when an interrupt is being services a new higher priority interrupt is raised?

Answer 24

» The interrupt currently being services is also added to a stack in memory and the new interrupy is serviced

Question 25

What is loaded in when the stack is popped?

Answer 25

» Retreive the previous values for the orignal program
» Carry on executing the original program where we left off

Question 26

What is a problem of paging?

Answer 26

» It could sperate the instructions inside a lopping condition so they are in different pages - very inefficient

Question 27

What are 3 similarities between paging and segmentation?

Answer 27

» Both allow programs to run despite insufficient memory
» Both are stored on a disk
» Pages and segments are transferred in to memory when needed

Question 28

What are 3 differences between paging and segmentation?

Answer 28

» Pages are fixed size. Segments are different sizes
» Pages are made to fit sections of memory. Segments are complete sections of memory
» Pages are physical divisions. segments are logical divisions

Question 29

What are 3 example of hardware interrupts?

Answer 29

» Power supply failure
» Power/reset button pressed
» Power down command - screen off

Question 30

What are 3 example of user interrupts?

Answer 30

» Moving the mouse
» Clicking/ tapping an icon to open a new program
» Keyboard presses

Question 31

What are 3 examples of software interrupts?

Answer 31

» illegal instruction encountered
» Arithmetic overflow
» New log-on request

Question 32

What is an example of timer interrupts?

Answer 32

» Screen - recording application

Question 33

What is an example of a input/output device interrupt?

Answer 33

» Buffer nearly empty

Question 34

What does a scheduler manage?

2 marks

Answer 34

» To process as many job as possible in the least amount of time
» Ensure all jobs are processed fairly - to maximise number of processes with fast respons times

Question 35

How does scheduling work?

Answer 35

» Process enters the ready queue
» Then enters the running state
» From here it will finish executing completely
» Get blocked, as it requires an input/ouput command

Question 35

How does scheduling work?

Answer 35

» Process enters the ready queue
» Then enters the running state
» From here it will finish executing completely
» Get blocked, as it requires an input/ouput command

Question 36

How does scheduling work?

Answer 36

» Process enters the ready queue
» Then enters the running state
» From here it will finish executing completely
» Get blocked, as it requires an input/ouput command

Question 37

What is First come first serve scheduling?

3 marks

Answer 37

» Processes are executed in the order they arrive
» If a process takes a long time, the others behind it simply have to wait
» The time the different process take to execute is irrelevant

Question 38

What is the short job first?

2 marks

Answer 38

» Picks the process that take the shortest amount of time and runs them until they finish
» Scheduler needs to know how long each process will take

Question 39

What is round robin?

3 marks

Answer 39

» Each process is allocated a fixed amount of time - known as time slice - or quantum
» If the process is not complete by the end of its time slice, it returns to the back of the ready queue
» Repeats until all users serviced
» Time slices are fractions of a second

Question 40

What is shortest remaining time?

Answer 40

» The scheduler estimates how long each process will take
» Picks the one that will take the least amount of time
» It is pre-emptive

Question 41

What is pre-emptive?

Answer 41

» This means that if hasnt completed after a certain amount of time, the scheduler checks to see whether any shorter processes have been added, if so it switches to them

Question 42

What is a multi-level feedback queue?

Answer 42

» If the computer has more tha none processer or processor core - it can handle more than one process queue at a time
» Different queues have different level of priorities
» Scheduler can move jobs between the different queues as needed

Question 43

What is processor starvation?

Answer 43

» When a particular process does not receive enough processor time in order to execute and be completed
» Occurs in shortest job first

Question 44

Explain why the first come first sever method may not be efficient?

2 marks

Answer 44

» Once a job starts it prevents another job from being processed
» A job using a slow resource wastes processor time

Question 45

Explain why scheduling is necessary?

4 marks

Answer 45

» Process as many jobs as possible
» In the least amount of time
» Ensure all jobs are processed farily
» Efficient use of resources/processer time
» Prevent processes from being starvated

Question 46

Describe how virtual memory is used?

Answer 46

» Use of secondary storage as it if was main memory
» Swap pages between memory and secondary storage

Question 47

Explain why interrupts are used in a computer system?

2 marks

Answer 47

» To obtain processor time
» For a device that needs to be serviced
» To avoid delays

Question 48

Give one example of an interrupt that allows the job to be resumed after the system has serviced the interrupt?

Answer 48

» User interrupt - e.g new long on request