4: Operating Systems

Question 1

What are the 5 types of scheduling algorithm?

Answer 1

• RR (Round Robin)
• SRT (Shortest Remaining Time)
• MFQ (Multi-level Feedback Queue
• FCFS (First Come First Served)
• SJF (Shortest Job First)

Question 2

Which of the scheduling algorithms are pre-emptive?

Answer 2

• RR
• SRT
• MFQ

Question 3

Which of the scheduling algorithms are non pre-emptive?

Answer 3

• FCFS
• SJF

Question 4

How does RR (Round Robin) work?

Answer 4

Each process is given a maximum length processor time in the running state after which it is put back into the ready queue

Question 5

How does SRT (Shortest Remaining Time) work?

Answer 5

The ready queue is sorted on the estimated time to complete the process. Processes that arrive having a shorter time to complete than the current running process are moved to the running state

Question 6

How does MLFQ (Multi-level Feedback Queue) work?

Answer 6

Several ready queues are used each with a different scheduling algorithm. Jobs are able to move between queues as their priorities change

Question 7

How does FCFS (First Come First Serve) work?

Answer 7

The first job to enter the ready queue is the first to enter the running state

Question 8

How does SJF (Shortest Job First) work?

Answer 8

Jobs are sorted in the ready queue according to the estimated processor time needed and are ran until they are finished

Question 9

What is a device driver?

Answer 9

Software that tells the operating system how to communicate with a device

Question 10

What is a virtual machine?

Answer 10

A program that has the same functionality as a physical computer

Question 11

What is segmentation?

Answer 11

the division of complete sections of programs into logical divisions of different sizes to allow it fit into main memory

Question 12

How does the operating system perform multi-tasking?

Answer 12

• The processor allocates a small amount of time to each process and cycles between them
• As this happens so quickly, it appears as if multiple programs are executing simultaneously

Question 13

How does the operating system help with file management?

Answer 13

• An extension to the file name tells the operating system which application to load the file into
• An operating system may present a logical structure of files in folders and allow the user to rename, delete, copy and move files

Question 14

How does the operating system deal with user management?

Answer 14

• The operating will allow multiple users to log into the same computer by retaining settings for each user such as icons, desktop backgrounds etc
• each user may have different access rights to files and programs
• A client-server network may impose a fixed or roaming profile for a user and manage login requests to the network

Question 15

How does the operating system deal with a user interface

Answer 15

• uses a WIMP interface (windows, icons, menus and pointers)
• WIMP is interactive, visual, intuitive and optimised for mouse and touch gesture input

Question 16

What is paging?

Answer 16

• Physical divisions of programs that are fixed in size
• paging takes no account of how it splits the program, only that it splits it into fixed-sized pages made to fit sections of memory

Question 17

What is virtual memory?

Answer 17

• If physical memory is running low, virtual memory must be used
• Applications stored in RAM that haven’t been used in a while are transferred to memory on the hard disk (virtual memory) in order to free up space in RAM for other applications
• If those applicationd are needed again, they are sent out of virtual memory and back into RAM and another application is swapped in its place
• if more time is spent moving pages/segments from memory to the disk (thrashing) than processing instructions, the computer will be very slow

Question 18

What is an interrupt?

Answer 18

Signal from hardware or software indicating that an event has occurred or that a process needs attention.

Question 19

What is an interrupt service routine?

Answer 19

The software with a set of instructions that halt the execution of the CPUs current program to allow for the operations of the interrupt to be carried out

Question 20

When the interrupt is complete, how will the processor know to continue the previously executed program?

Answer 20

• When an interrupt is received, the values held in the registers are copied into a data structure in the memory known as the stack
• These values are pushed onto the stack in a stack frame, effectively saving them for later retrieval
• The interrupt can now be executed
• Once the interrupt is complete, the frame is then popped off the top of the stack, allowing for the retrieval of the previous values for the original program, which can then be loaded back into the processor registers and executed

Question 21

Examples of hardware interrupts

Answer 21

• Power supply failure
• Power/reset button pressed
• Power-down command

Question 22

Examples of user interrupts

Answer 22

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

Question 23

Examples of software interrupts

Answer 23

• Illegal instruction encountered
• Arithmetic overflow
• New log-on request

Question 24

Examples of interrupts on input/output devices

Answer 24

• Buffer nearly empty
• Signal the completion of a data transfer to/from a device
• Printer ink supply notification

Question 25

How does a multi-tasking operating system work?

Answer 25

Each active program is scheduled to receive a tiny time slice in quick rotation, giving the impression they are operating at the same time

Question 26

How do multi-user operating systems work?

Answer 26

- The computer manage the user's various permissions and access rights when they log on - Server operating system software will handle the requests of multiple people using different computers on a network at the same time

Question 27

how does a distributed operating system work?

Answer 27

- you can combine the processing power of multiple computers across a network for a single task - the operating system controls and coordinates the computers, presenting them to the user as if they were a single system

Question 28

how do embedded operating systems work?

Answer 28

- they tend to run on dedicated hardware so they run with maximum efficiency, using low-powered processors and very little memory - examples include washing machines, home assistants, traffic lights

Question 29

How does real-time operating systems work?

Answer 29

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