Systems 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 computer

Question 2

Give the functions of an operating system

Answer 2

• Memory management
• Resource management
• Input/Output management
• Interrupt management
• Security
• User interface
• 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 is used to act as RAM
• Sections of programs not currently being used are temporarily moved into virtual memory through paging
• This frees up memory for other programs in RAM

Question 5

What is an interrupt

Answer 5

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

Question 6

Explain the stages of the Interrupt Service Routine

Answer 6

• Interrupt register checked at the end of each Fetch-Decode-Execute cycle.
• If there is an interrupt exists with a higher priority to the current process, the current contents of the registers in the CPU are transferred into a stack.
• The relevant interrupt service routine (ISR) is loaded into RAM.
• A flag is set to signal the ISR has begun.
• The flag is reset once the ISR has finished.
• Interrupt register checked again. If interrupts are of a higher priority, the process is repeated.
• If there are no interrupts with a higher priority, the contents of the stack are popped and place back into the special memory registers
• The fetch-Decode-Execute cycle renews as before

Question 7

Are these scheduling algorithms pre-emptive or non pre-emptive?
FCFS, SRT, SJF, MLFQ, RR

Answer 7

Pre-emptive: RR, SRT, MLFQ
Non-preemptive: FCFS, SJF

Question 8

What are the advantages and disadvantages of using Multilevel Feedback Queues for scheduling?

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 eg. life support systems, self-driving cars, power systems

Question 10

Describe three functions of the BIOS

Answer 10

Running tests upon the computer’s start up:
● POST (Power-on self test) which ensures that all hardware is correctly connected and functional
● Checking the CPU clock, memory and processor
● 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

● Testing programs
● Protection from malware
● 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