1.2.1 System Software

Question 1

What is an operating system

Answer 1

A collection of programs that work together to provide an interface between the user and the computer

Question 2

Give 3 functions of the operating system

Answer 2

Memory, Resource, I/O and Interrupt management, Security, User Interface and Utility software.

Question 3

What are the similarities and differences between paging and segmentation

Answer 3

Both: Are used when RAM space is insufficient, can cause disk thrashing
Paging: Uses equal-sized sections called pages
Segmentation: Uses variable-sized, logical sections called segments

Question 4

Describe how virtual memory is used when there is not enough RAM

Answer 4

A section of the hard drive acts as RAM.
Sections of programs currently not being used are moved into virtual memory through paging.
This frees up memory in the RAM for other programs.

Question 5

What is an interrupt

Answer 5

A signal generated by software of hardware to indicate to the processor that a process needs attention.

Question 6

Explain the Stages of the Interrupt Service Routine

Answer 6

1. Interrupt register is checked at the end of FDE cycle.
2. If there is an interrupt with higher priority than the current process, the current contents of the registers in the CPU are transferred into a stack.
3. The interrupt service routine is loaded into RAM and the ISR is executed.
4. If there are no interrupts with a higher priority, the contents of the stack are popped back into the registers in CPU.

Question 7

Are these scheduling algorithms pre-emptive or non pre-emptive? First Come First Serve, Shortest Remaining Time, Shortest Job First, Round Robin and Multi Level Feedback Queue

Answer 7

Pre-emptive: Round Robin, Shortest Remaining Time, Multi Level Feedback Queue
Non pre-emptive: First Come First Serve, Shortest Job First

Question 8

What are the advantages and disadvantages of Multi Level Feedback Queues?

Answer 8

Advantage: Services most urgent interrupts first
Disadvantage: Hard to implement

Question 9

Define a real time operating system and when it may be used.

Answer 9

Real time operating systems perform a task within a guaranteed time frame. They are used in systems were a response within a given time frame is critical e.g life support systems, self driving cars, power systems.

Question 10

Describe three functions of the BIOS

Answer 10

1. Running POST (Power-on self test) which ensures that all hardware is correctly connected and functional
2. Checking the CPU clock, memory and processor.
3. Testing for external memory devices

Question 11

What is the role of a device driver?

Answer 11

Enable the operating system to interact with hardware devices

Question 12

Describe an instance in which a virtual machine may be used.

Answer 12

1. Testing programs
2. Protection from malware
3. Running software compatible with different versions and types of operating systems

Question 13

Give one advantage and one
disadvantage of intermediate code

Answer 13

Advantage: Platform independent, portable
Disadvantage: Slower execution