1.2.1 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 3 functions of an Operating System:

Answer 2

Three from:

Memory management
Resource management
I/O 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 FDE cycle
• If there is an interrupt that exists with a higher priority, 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 sent to signal the ISR has begun
• The flag is reset once the ISR is 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 placed back into the special memory registers
• The FDE cycle renews as before

Question 7

Which scheduling algorithms are preemptive and which ones are non-preemptive?

(First come first serve, shortest remaining time, shortest job first, multi-level feedback queues, round robin)

Answer 7

Preemptive: RR, SRT, MLFQ

Non-preemptive: FCFS, SJF

Question 8

What are the advantages and disadvantages of using Multi-Level 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

Perform tasks within a guaranteed time frame (critical).

Examples include life support systems, self-driving cars, etc.

Question 10

Define three functions of BIOS

Answer 10

• POST (power on self test) which ensures that are hardware is correctly connected and functional
• Checking the CPU a lock, memory and processor
• Testing for external memory devices

Question 11

What is the role of a device driver?

Answer 11

Enable the OS to interact with hardware devices

Question 12

Describe an instance in which a VM may be used:

Answer 12

Any from:

• Testing programs
• Protection from malware
• Running software compatible with different versions and types of OS

Question 13

Give one advantage and one disadvantage of intermediate code:

Answer 13

Advantage: Platform independent, portable

Disadvantage: Slower execution

Question 14

Define Pre-emptive:

Answer 14

OS that actively start and stop jobs

eg. Multi-Level Feedback Queues, Shortest Remaining Time, Round Robin

Question 15

Define Non Pre-emptive:

Answer 15

Once a job starts, the OS leaves it alone until it’s completed

eg. First Come First Served, Shortest Job First