2. Introduction to Operating Systems

Question 1

What happens when a programs run?

Answer 1

The processor fetches instructions from memory, decodes the instructions and executes them.

Question 2

What is virtualisation?

Answer 2

Taking a physical system and creating a virtual form of it.

Question 3

What is an operating system?

Answer 3

It is a body of software that makes it easy to run programs, allows programs to share memory and enables programs to interact with devices.

Question 4

What are resources?

Answer 4

Anything valuable such as CPU, memory and disk.

Question 5

What is the result of virtualising CPU?

Answer 5

An illusion to processes where each of them seem to have an individual dedicated CPU.

Question 6

How does memory work?

Answer 6

It is a just an array of bytes where we can read and write to store information.

Question 7

What is the result of virtualising memory?

Answer 7

An illusion to processes where each of them seem to have an individual dedicated physical memory.

Question 8

What is concurrency?

Answer 8

Working on many things at once in the same program.

Question 9

What is a thread?

Answer 9

It is a lightweight function that runs in the same process, where they share the same memory space, data, code with other threads. The only thing they don’t share is the stack pointer.

Question 10

What is persistence?

Answer 10

Managing files stored in the disk space to prevent ease of data loss in memory.

Question 11

What is protection?

Answer 11

Ensuring that malicious behaviours do not affect other processes

Question 12

What are the goals of an operating system?

Answer 12

1. Provide high performance
2. Protection
3. Isolation
4. Energy-efficient
5. Security
6. Mobility

Question 13

What is batch processing?

Answer 13

Setting up a number of jobs and running them in a batch by computer operators.

Question 14

What is a system call?

Answer 14

A mechanism to request a service from the operating systems with special pair of hardware instructions and hardware state.

Question 15

What is a procedure call?

Answer 15

A standard function calling mechanism.W

Question 16

What is the difference between system calls and procedure calls?

Answer 16

System call transfers control to operating systems while raising the hardware privilege level.

Question 17

What is user mode?

Answer 17

A privilege level where applications have restricted access to hardware.W

Question 18

What is kernel mode?

Answer 18

A privilege level where OS has the full access to hardware.W

Question 19

What is a trap?

Answer 19

A special hardware instruction that is encountered when a process tries to access a system call or when it throws an exception.

Question 20

What is a trap handler?

Answer 20

A set of instructions that should be executed based on the problem that caused the trap. For example, exceptions or system calls.

Question 21

What is a return-from-trap instruction?

Answer 21

An instruction that reverts kernel mode to user mode and passes the control back to the application.