1.2.1 Systems Software

Question 1

What is the need of an “Operating System”?

Answer 1

It manages the hardware and the programs running on the system.

Question 2

What examples of “Operating Systems” are there?

Answer 2

Windows, OS X, Linux, iOS and Android.

Question 3

What different roles does the “Operating System” have?

Answer 3

Managing the hardware of the system;
Managing programs installed on the system and the those being run;
Managing the security of the system;
Providing the user with an interface that they can use.

Question 4

What types of “Memory Management” are there?

Answer 4

Paging, Segmentation and Virtual Memory.

Question 5

What is the purpose of “Memory Management”?

Answer 5

The OS has to ensure that memory is used efficiently without wasting space, and that data is stored securely so that data from different programs don’t interfere with each other.

Question 6

What is “Paging”?

Answer 6

The process of dividing programs physically into equal-sized blocks.

Question 7

What is “Segmentation”?

Answer 7

The process of dividing programs logically into blocks containing modules or routines.

Question 8

Why is programs stored in memory divided into sections?

Answer 8

Because storing the entire program is wasteful, as the entire program is most likely not being used at a single team.

Question 9

What is “Virtual Memory”?

Answer 9

This is the process of segmenting part of the Secondary Storage to be used as Main Memory.

Question 10

Why is “Virtual Memory” used?

Answer 10

Because RAM (Main Memory) is much more expensive than ROM (Secondary Storage), and there is often hundreds of times more Secondary Storage than Main Memory, parts of the Secondary Storage is used as Main Memory if it is needed, to increase speed of the system and compensate for any Bottlenecking that may be occurring.

Question 11

What is “Disk Thrashing”?

Answer 11

When parts of Secondary Storage is temporarily converted into Virtual Memory, it can also convert back and forth depending on what it is needed for, allowing for the store of data, as well as the store of the current programs being run. If this swap back and forth happens too often, Disk Thrashing occurs.

Question 12

What is an “Interrupt”?

Answer 12

A Control Signal that is triggered when a device is in need of attention. Each Interrupt has a certain priority, meaning some Interrupts can overpower others.

Question 13

When are the only times a NEW “Interrupt” can take effect immediately?

Answer 13

If the task currently being attended to has a lower priority than the new Interrupt.

Question 14

What happens during the “ISR” (Interrupt Service Routine)?

Answer 14

The contents of the PC and other registers are copied to a stack;
The ISR can then be loaded by changing the PC to the value of where the ISR is in memory;
When the ISR is complete, the previous values of registers stored in the stack are restored from memory to the CPU.

Question 15

When does the OS run an “ISR”?

Answer 15

If the OS finds an Interrupt with higher priority than the current task at the end of the Fetch-Decode-Execute cycle iteration, then the relevant ISR is run.

Question 16

What is a “Scheduler”?

Answer 16

A program that manages the amount of time different processes have in the CPU.

Question 17

What different types of “Scheduler” are there?

Answer 17

RR (Round Robin), First Come, First Serve (FCFS), Shortest Job First (SJF), Shortest Remaining Time (SRT), Multi-Level Feedback Queues (MLFQ).

Question 18

What is “Round Robin” Scheduling?

Answer 18

This is where each process is given a fixed amount of time to execute. If it isn’t finished at the end of this fixed time, then it rejoins the queue so that the next process can take its turn.

Question 19

What is “First Come, First Serve” Scheduling?

Answer 19

The top process in the queue is dealt with until it is completely finished, then the next process is dealt with until it is completely finished and so on.

Question 20

What is “Shortest Job First” Scheduling?

Answer 20

This is where the process in the queue that has the shortest execution time is dealt with until it is finished, and then the next process with the shortest process is dealt with and so on.

Question 21

What is “Shortest Remaining Time” Scheduling?

Answer 21

The scheduler estimates how much time each process in the queue will take to finish, and deals with the one that will take the least time. If a new process joins the queue that will take less time than the process currently being dealt with, then the new process is dealt with instead.

Question 22

What is “Multi-Level Feedback Queue” Scheduling?

Answer 22

This uses multiple queues that each have different priority to sort the processes based on their needs by the CPU.

Question 23

What types of “Operating System” are there?

Answer 23

Multi-Tasking, Multi-User, Distributed, Embedded, Real-Time.

Question 24

What is “Multi-Tasking” OS?

Answer 24

This is where multiple programs can be run at the same time.

Question 25

What is “Multi-User” OS?

Answer 25

This is where multiple users can use a system as well as access its resources simultaneously (not to be confused with a single system allowing different users).

Question 26

What is “Distributed” OS?

Answer 26

This is where multiple computer systems can work together on a single task.

Question 27

What is “Embedded” OS?

Answer 27

These are OS designed for embedded systems where a computer only forms part of the device, such as Washing Machines, Vending Machines, Dishwashers etc.

Question 28

What is “Real-Time” OS?

Answer 28

These are OS designed to carry out tasks in a set amount of time, even when it is left for long periods of time. Examples include Flight Simulators.

Question 29

What does “BIOS” stand for, and what does it do?

Answer 29

“Basic Input/Output System” is the thing looked to on system start-up to get the system properly up and running. This means the PC of the CPU points to the location of the BIOS.

Question 30

What type of memory is the “BIOS” stored on and why?

Answer 30

The BIOS is stored in Flash Memory so that it can be updated, as well as changed by the user, including changing things like boot order.

Question 31

What are “Device Drivers”?

Answer 31

Software usually supplied with new hardware to be used that tells the system how to communicate with the hardware.

Question 32

Why are “Device Drivers” used?

Answer 32

Because it would be impossible for manufacturers to program the hardware to individually know how to communicate with every type of device, so are used so the OS knows how to communicate with it.

Question 33

What is a “Virtual Machine”?

Answer 33

A program that has the same functionality as a physical computer system.

Question 34

Why are “Virtual Machines” used?

Answer 34

They are usually used to imitate the functionality of a physical computer, usually allowing the user to run a different operating system on a computer. This may be running Linux on a system that runs Windows, as it may be useful to test a program that is intended for multiple platforms.

Question 35

What is another example of a “Virtual Machine”?

Answer 35

Another example is converting Source Code into something called Byte Code. Because this isn’t Machine Code, it cannot be directly run on a processor, so a virtual machine is needed in order to interpret the Byte Code so it can be used. This makes a program highly portable.