SYSTEMS SOFTWARE

Question 1

What is an operating system

Answer 1

Software that controls the computer, manages the computer’s hardware and the programs running on it

Question 2

Examples of OS

Answer 2

Windows, MacOS, Linux, IOS and Android

Question 3

Roles of an operating systems

Answer 3

• Manage the system hardware
• Manage the installation and running of programs
• Manage the security of the system
• Provide a user interface
• Memory management

Question 4

What is paging

Answer 4

Programs are physically divided into equal-sized blocks called pages

Question 5

What is segmentation

Answer 5

Programs are logically divided into unequal blocks containing modules or routines

Question 6

What is virtual memory

Answer 6

The use of secondary storage as an extension of a computer’s physical memory

Question 7

What is disk thrashing

Answer 7

When pages are being swapped from main memory to virtual memory too often, slowing down the computer

Question 8

What is an interrupt

Answer 8

A signal sent to a CPU to signify another processor is in need of processing time

Question 9

What is the ISR

Answer 9

Interrupt Service Routine - This is the program code that is called when an interrupt is triggered

Question 10

What happens when an interrupt occurs

Answer 10

• The contents of the PC and other registers are copied to an area of memory called a stack
• The ISR can be loaded by changing the PC to the location of the ISR in memory
• When the ISR is completed the previous content is restored from the stack to the CPU

Question 11

What happens when an interrupt is being serviced, a higher priority interrupt occurs

Answer 11

The interrupt will be added to the stack and the new interrupt is serviced. After the previous interrupt is taken off the stack and continued

Question 12

What is scheduling

Answer 12

The method an OS uses to ensure all processes get sufficient processor time

Question 13

Describe the round robin algorithm

Answer 13

Each process is given a fixed amount of time. If it hasn’t finished by the end of that time period, it goes to the back of the queue so the next process in line can have its turn

Question 14

Describe the first come first served algorithm

Answer 14

The first process to arrive is dealt with by the CPU until it’s finished. Any other processes that come along are queued up waiting for their turn

Question 15

Describe the shortest job first algorithm

Answer 15

Picks the job that will take the shortest time and run it until it finishes

Question 16

Describe the shortest remaining time algorithm

Answer 16

The scheduler estimates how long each process will take. It then runs the one that will take the least amount of time. If a process hasn’t completed after a certain amount of time, the scheduler checks to see whether any shorter process have been added

Question 17

Describe the multilevel feedback queues algorithm

Answer 17

Uses multiple queues. Each of these queues has a different priority. The algorithm can move jobs between these queues depending on the jobs behaviour

Question 18

Describe distributed OS and an example where it is used

Answer 18

Allows multiple computers to work together on a single task. They tend to be used in systems aimed at completing computationally intensive tasks.
e.g 3D animation

Question 19

What are embedded systems and an example of one

Answer 19

A dedicated computer system that performs one or more specific functions within a larger piece of equipment.
e.g, washing machines, vending machines

Question 20

Describe multitasking OS

Answer 20

Can run multiple programs simultaneously

Question 21

Describe multi-user OS and an example where it is used

Answer 21

Allows multiple users to use a system and its resources simultaneously.
e.g Banks and retailers

Question 22

Describe real-time OS and an example where it is used

Answer 22

Designed to carry out actions within a guaranteed amount of time even when left running on long periods. Usually the expected response time is within a small fraction of a second
e.g autopilot

Question 23

What is the BIOS

Answer 23

Basic Input/Output System - The program a computer’s microprocessor uses to start the computer system after it is powered on

Question 24

What is a device driver

Answer 24

A piece of software that tells the computer how it can communicate with hardware

Question 25

What is a virtual machine

Answer 25

A program that has the same functionality as a physical machine

Question 26

Uses of virtual machines

Answer 26

• Run one OS within another OS
  - a program needed that can’t run on the host OS
  - offers a convenient way to test a program being developed on multiple platforms
• Interpreting intermediate code