Operating Systems

Question 1

What is an Operating System?

Answer 1

A program that controls the execution of Application Programs and acts as an interface between applications and the Computer Hardware.

Question 2

What are the 5 services provided by the OS?

OS = Operating System

Answer 2

File Management, I/O Management, Process Management, Memory Management, Multiprocessor Management

Question 3

What is the Kernel?

Answer 3

A central part of the OS containing a range of functionality depending on design.

Question 4

What is Kernel Mode?

Answer 4

Mode in the OS that allows you unrestricted access to memory, and access to all instructions.

Question 5

What is User Mode?

Answer 5

A mode in the OS that only allows access to certain areas of memory and doesn’t allow access of privileged instructions.

Question 6

What is a context switch?

Answer 6

Changing from Kernel mode to user mode and vice versa.

Question 7

Which mode do Applications run in?

Answer 7

User Mode

Question 8

What does a context switch involve?

Answer 8

This is computationally expensive and requires moving data in and out of registers, memory management etc

Question 9

What are the four types of Kernel?

Answer 9

Monolithic, Layered, Microkernel, Modular

Question 10

What are the features of a Monolithic Kernel?

Answer 10

All services are implemented by a large kernel, any new features are added directly to the kernel, everything is connected to everything.

Question 11

Advantage of a Monolithic Kernel:

Answer 11

Fast communication within kernel.

Question 12

Disadvantages of a Monolithic Kernel:

Answer 12

Difficult to understand and modify, lots of dependencies. Lack of security, new includes gain access to all memory locations and all processes.

Question 13

What are the features of a Layered Kernel?

Answer 13

Services implemented by a large Kernel with a layered organisation. Different tasks are implemented by a specific layer, and each layer can only communicate with adjacent layers.

Question 14

Advantages of a Layered Kernel:

Answer 14

Easy to debug due to modular design

Question 15

Disadvantages of a Layered Kernel:

Answer 15

Poor performance due to having to move through multiple layers to obtain OS service. no direct communication.

Question 16

What are the features of a Microkernel?

Answer 16

Has services implemented by servers and a small kernel delivers messages between them. Idea that If it doesn’t have to be in the Kernel put it in user mode.

Question 17

Advantages of a Microkernel:

Answer 17

Secure and reliable, executions done in user mode where restricted processes can’t be accesses.

Question 18

Disadvantages of a Microkernel:

Answer 18

Poor Performance due to increased system function overhead, no direct communications allowed.

Question 19

What are the features of a Modular Kernel:

Answer 19

Start with a small kernel and additional services are added loaded on via modules. OS must work equally with and without each module. no dependencies between modules.

Question 20

Advantages of a modular Kernel:

Answer 20

Fast due to not needing to load unnecessary services, modules can communicate directly with other modules.

Question 21

Disadvantages of a Modular Kernel:

Answer 21

Like a Monolithic Kernel as more modules are loaded.

Question 22

What does a Virtual Machine do?

Answer 22

A host OS provides simulated virtual hardware for one or multiple OS’s.