211 - Operating Systems

Question 1

What are the functions of a operating system?

Answer 1

• It is an interface between User and Hardware
• Allocates resources to each user to ensure everyone has a fair share
• Managed the memory and security etc

Question 2

What is the purpose of an OS

Answer 2

• Convenience

- Efficiency

Question 3

Processes have 1 or more thread….

Answer 3

Small sequences of instructions managed independently by schedular

Question 4

Benefit of threads

Answer 4

Fast and efficient

Question 5

What is concurrency?

Answer 5

The act of managing and running multiple computations at the same time

Question 6

What happens if a thread goes first and another one goes last?

Answer 6

It should have the same outcome

Question 7

An interface in Java and how to implement it

Answer 7

Runnable and must have “public void run() as it’s method signature to implement it

Question 8

What are the 3 central concepts in concurrent programming?

Answer 8

1. Processor (ingredients)
2. Program (recipe)
3. Process (food you make)

Question 9

Which is correct?

A program can have multiple processes

Or

A process can have multiple programs

Answer 9

A program can have multiple processes such as clicking on google chrome 10 times and getting 10 different windows

Question 10

What is context switching?

Answer 10

Swapping from one process to the other quickly

Question 11

Which is correct?

Processes are always parallel but not always concurrent

Or

Processes are always concurrent but not always parallel

Answer 11

Processes are always concurrent but not always parallel

Question 12

What is parallelism?

Answer 12

The act of running multiple computations simultaneously

Question 13

Weakness of a schedular

Answer 13

It is always adversarial so you expect it to do the worst possible thing

Question 14

Benefits of multiprocessor systems

Answer 14

1. Increased throughput
2. Economy of scale
3. Increased reliability

Question 15

When is concurrency safe to do?

Answer 15

When not sharing data and when handling read only data

Question 16

What is Moore’s law and what’s wrong with it today?

Answer 16

It no longer applies because the transistors get so small that electrons are able to jump over each other due to the lack of space which causes data to be entered in wrong.

Also generates a lot of heat which can cause the hardware to overheat and it’s difficult and expensive to ensure systems don’t overheat

Question 17

What is Amdahl’s law?

Answer 17

Speed up is limited by the serial part of the program

Question 18

What is synchronisation?

Answer 18

A mechanism to ensure multiple concurrent processes or threads do not simultaneously execute some particular program segment

Question 19

What is competition?

Answer 19

Competing for a variable that processes want to reach simultaneously

Question 20

What is the difference between deterministic and indeterminate?

Answer 20

Deterministic is same output each time and indeterminate is different output each time

Question 21

What does cooperation do?

Answer 21

It manages the offset or time to ensure threads travel across system resources correctly

Question 22

What is a critical section?

Answer 22

It is a code section that access a shared resource

Question 23

What is mutual exclusion?

Answer 23

Only one thread can run within the critical section at any given time

Question 24

What is a race condition?

Answer 24

An error that occurrs due to multiple processes ‘racing’ in an uncontrolled manner through a section of non-atomic code

Question 25

What is a semaphore?

Answer 25

It’s either a closed or open condition. When closed, there is no entry, when open there is entry like red and green traffic lights

Question 26

What operations does a semaphore support?

Answer 26

Wait() and signal()

Question 27

What does a schedular do?

Answer 27

It maintains the queue or processes.

Question 28

What are zombie processes?

Answer 28

Threads that are stuck in memory waiting forever to be run. So we must use (public synchronised void) to ensure it doesn’t happen

Question 29

What do you have to consider when using Notify() and NotifyAll()?

Answer 29

If you do NotifyAll() you must use while loops as while loops check the condition over and over and for Notify() you can use the if statement as it checks the condition only once.

Question 30

How do you turn a semaphore into a lock?

Answer 30

They are a common type of exclusion lock, by giving it a binary value, it acts like a lock.

Question 31

What is polymorphism?

Answer 31

An instance of a class which inherits from (extends) another can also be treated like an instance of that class