1.2.1

Question 1

What is an operating system?

Answer 1

A collection o programs that work together to provide an interface between the user and computer

Question 2

Name some functions of an operating system:

Answer 2

-memory management
-resource management
-user interface
-utility software

Question 3

What is resource management/multitasking?

Answer 3

-Multitasking – when you have more than one program open and running at the same time.
-The processor allocates a small amount of time to each process and cycles between them. ​
-appears to be simultaneous

​

Question 4

What is file management?

Answer 4

-Data is stored in files
-An extension to the filename tells the OS which application to load the file into
-The OS may present a logical structure of files in folders and allow the user to rename, delete, copy and move files

​

Question 5

What is user management/security?

Answer 5

-User management – allows multiple users to log into the same computer
-OS will retainsettings for each user
-may have differentaccess rights

Question 6

What is a user interface?

Answer 6

-WIMP – windows, icons, menus and pointers​
-Interactive​, Intuitive​
-Optimised for mouse and touch gesture input

​

Question 7

What is paging?

Answer 7

-pages are fixed size
-physical divisions
programs are split up to fit into a given number of pages

Question 8

What is segmentation?

Answer 8

-fixed sizes
-logical divisions
-complete sections of code

Question 9

Similarities between paging and segmentation:

Answer 9

-both allow programs to run despite insufficient memory
-stored on disk
-transferred into memory when needed

Question 10

What is virtual memory?

Answer 10

-when RAM is full, VM is used
-sections of programs not currently being used are temporarily moved into VM through paging
-frees up memory in RAM

Question 11

What is an interrupt?

Answer 11

A signal generated by software/hardware to indicate that the processor requires attention

Question 12

What is the interrupt service routine (ISR)?

Answer 12

a program with a set of instructions that need to be fetched, decoded and executed to carry out the operations of the interrupt

Question 13

What happens when the CPU receives an interrupt:

Answer 13

-complete the current FDE cycle
-check priority of interrupt
-if its higher…
-values held in registers are pushed onto the stack
-interrupt is executed
-pop the frame off the top of the stack
-load values back into registers
-carry on with FDE cycle

Question 14

What is scheduling?

Answer 14

-In a multi-user environment, a number of users will need servicing, seemingly at the same time so will need a scheduler

Question 15

First come first serve (FCFS):

Answer 15

-Processes are executed in the order they arrive
-not pre-emptive

Question 16

Shortest job first (SJF):

Answer 16

-Picks the processes that take the shortest amount of time and runs them until they finish
-not pre-emptive

Question 17

Round Robin (RR):

Answer 17

-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
-pre-emptive

Question 18

Shortest time remaining (STR):

Answer 18

-the ready queue is sorted by the estimated time to complete the process
-pre-emptive

Question 19

Multi-level feedback queues (MLFQ):

Answer 19

-several ready queues are used, each with a different scheduling algorithm
-jobs are able to move between queues as their priorities change
pre-emptive

Question 19

What does pre-emptive mean?

Answer 19

-Jobs are actively made to start and stop by the operating system

Question 20

What does non pre-emptive mean?

Answer 20

-Once a job is started, it is left alone until it is completed

Question 21

What are the different types of operating systems?

Answer 21

-distributed
-multitasking
-multi-user
-embedded
-real time