1.2.1 - Systems Software

Question 1

What is the primary purpose of an operating system?

Answer 1

To manage the hardware and provide a user interface.

Question 2

What other tasks are operating systems in charge of?

Answer 2

• File management
• Memory management
• Device drivers
• Multiple users
• Interrupt handling
• Application software.

Question 3

What is multitasking?

Answer 3

When more than one program is currently running.

This means that the operating system has to allocate time for each program and quickly cycles between each program, so quickly that it appears as the programs are running at the same time.

Question 4

How does the user interface provided by the OS work?

Answer 4

The user interface is made up of interactable Windows, Icons, Menus and Pointers (WIMP) which allow the user to interact with the operating system and carry out any task.

Question 5

What are the main differences between paging and segmentation in main memory?

Answer 5

Paging: Pages are all equal size and programs can be made up of multiple of these pages. Pages are PHYSICAL divisions of main memory.

Segmentation: Segments are different sizes and are complete sections of programs. They are LOGICAL divisions in main memory so if a program is too big to fit into one space, it can be divided into parts and placed in the available slots.

Question 6

How does virtual memory work?

Answer 6

• If main memory is full, program B is loaded into secondary storage and when needed, program A in main memory that is not being used right now is replaced by the program B which was in secondary storage.
• Remember that since it takes time to move the programs from main memory to secondary and back, using virtual memory can significantly decrease performance!
  -Needs free secondary storage

Question 7

How are interrupts handled?

Answer 7

When the CPU fetches decodes and executes, after executing it checks for interrupts as well. When an interrupt is raised by the CPU, the processor must stop what it is doing in order to deal with this problem so the interrupt service routine is run.

Question 8

What is the interrupt service routine?

Answer 8

It is a set of instructions that need to be followed in order to carry out the interrupt’s instructions. This means that the program counter must be changed to the address of the instructions in the interrupt.

Question 9

What happens when the interrupt is complete?

Answer 9

When an interrupt is received, the values held in the registers are copied onto a stack for later use and when the interrupt is complete, the values are popped out of the stack to be used and to continue executing the program which was stopped in order to deal with the interrupt.

Question 10

What are examples of interrupts?

Answer 10

• Input by the user such as keyboard and mouse input
• Errors such as overflow and instruction failure
• Power button is pressed

Question 11

What is scheduling?

Answer 11

This is a method used by multitasking operating systems in order to carry out multiple tasks “at the same time”.

Question 12

How does scheduling work?

Answer 12

A scheduler manages what programs to execute next and for how long. This scheduler uses a ready queue where programs and instructions line up to be executed by the CPU.

Question 13

Scheduling - First Come First Serve

Answer 13

Processed are executed in the order in which they arrive and for as long as they need so the programs further back in the queue will have to wait longer for the ones in front to finish executing.

Question 14

Scheduling - Shortest Job First

Answer 14

Processes are queued in order of shortest time. Processes that take the shortest time are placed at the front and processes which take the longest are placed at the back.

Question 15

Scheduling - Round Robin

Answer 15

Every process is given a time slice (or quantum) so each process has the same time in the CPU and if the process needs longer, it is placed to wait at the back of the queue.

Question 16

Scheduling - Shortest Remaining Time

Answer 16

Similar to Shortest Job First but is a pre-emptive algorithm which means that processes can be suspended when a higher priority one joins the queue, the lower priority one that was just in the CPU is suspended and goes to the back of the line while the higher priority one is being executed.

Question 17

What is process blocking in scheduling?

Answer 17

If a process requires more data, the process is blocked until that data has been fetched and delivered to the process. Once this has happened, a interrupt is generated to let the scheduler know this process is ready to join the queue again.

Question 18

How do Multi-level Feedback Queues work?

Answer 18

Instead of having one ready queue, there are multiple queues. These queues are seperated into different priorities and processes are placed in different queues based on their processing needs by the CPU. So processes which require little time in the CPU are preferred and ones that require higher processing have to wait in a waiting queue for the higher priority processes.

Question 19

Whats are the different types of operating systems?

Answer 19

• Distributed
• Embedded
• Real time
• Multi tasking
• Multi user

Question 20

How does distributed computing work?

Answer 20

The operating system controls all the participating computers and their processing power together all to achieve a certain goal or task.

This is how DDOS attacks work too as malware infected computers can be used to send overwhelming amounts of requests to a website or service which might not be able to handle all the traffic.

Question 21

What are embedded operating systems?

Answer 21

They run on low power and low processing power CPUs with max efficiency and on dedicated hardware such as a washing machine or a microwave. They mostly have a specific function and purpose.

Question 22

What are real time operating systems?

Answer 22

They are used in environments which need maximum safety and responsiveness such as hospitals and self driving cars. They are built with extra redundancy and do not usually operate with maximum capacity in order to be able to respond to rare but critical situations which require extra processing power.

Question 23

What is the BIOS?

Answer 23

The Basic Input Output System is a set of instructions in charge of loading the operating system when the computer is turned on. It also first does a check to make sure all the hardware is working.

The BIOS is stored in ROM.

Question 24

What are device drivers?

Answer 24

Software that allows the operating system to communicate with external hardware such as a printer or a projector. It acts as a translator to translate the OS instructions to instructions that this external hardware can understand.

Question 25

What is a virtual machine?

Answer 25

This is a program that can be run on a computer to simulate the operating system for any other device.

Examples of this are emulators which can run operating systems but not on their native hardware.

Question 26

What is a virtual server?

Answer 26

This is a technique which is used to spread many virtual servers on a smaller number of physical servers and allows for better versatility when there is higher demand for the servers or for when one is not working.

Question 27

What is intermediate code?

Answer 27

This is standard code that can be run on many different programs and creates portable code.

An example of this is Java code which can be run on many devices and is translated via a Java virtual machine which can be run on the device to translate the java code into more specific machine code.