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 the 7 functions of an operating system.

Answer 2

Memory management
Resource management
Input/Output management
Interrupt management
Security
User interface
Utility software

Question 3

Why are paging & segmentation used?

Answer 3

To manage memory to avoid disk thrashing

Question 4

What is disk thrashing?

Answer 4

Slowed system performance
Occurs when operating system uses disk for memory due to excessive & frequent reading or writing operations

Question 5

What is paging?

Answer 5

A memory management technique that divides memory into fixed-sized sections called pages

Question 6

What is segmentation?

Answer 6

A memory management technique that divides memory into variable-sized, logical sections called segments

Question 7

Describe how virtual memory is used.

Answer 7

A section of hard drive is used to act as RAM
Sections of programs not currently being used are temporarily moved into virtual memory throuugh paging
Frees up memory for other programs in RAM

Question 8

What is an interrupt?

Answer 8

A signal generated by software or hardware to indicate to the processor a need for immediate attention

Question 9

Outline the stages of the Interrupt Service Routine.

Answer 9

Interrupt register checked at end of each FDE cycle
If an interrupt with a higher priority than the current process exists, the contents of the registers are transferred onto stack
Relevant ISR is loaded into RAM
A flag is set to signal ISR has begun & reset once ISR is finished
Interrupt register checked again, process is repeated if any of higher priority found
When there are no interrupts with higher priority, the contents of the stack are popped off and loaded back into registers
The FDE cycle renews as before

Question 10

Name the 5 scheduling algorithms.

Answer 10

Round Robin (RR)
Shortest Remaining Time (SRT)
Shortest Job First (SJF)
Multi-Level Feedback Queue (MLFQ)
First Come First Served (FCFS)

Question 11

Which scheduling algorithms are pre-emptive?

Answer 11

Round Robin
Shortest Remaining Time
Multi-Level Feedback Queue

Question 12

Which scheduling algorithms are non-preemptive?

Answer 12

First Come First Served
Shortest Job First

Question 13

Describe the First Come First Served scheduling algorithm.

Answer 13

The first job enqueued is the first to enter the running state

Question 14

Describe the Shortest Job First scheduling algorithm.

Answer 14

Sorts the jobs in order of expected time to complete

Question 15

Describe the Shortest Job First scheduling algorithm.

Answer 15

Sorts the jobs in order of expected time to complete

Question 16

Describe the Round Robin scheduling algorithm.

Answer 16

Gives each job a maximum length of processor time
Once the time is complete, the job is put to the back of the queue and the job at the front is passed to the processor
If a job completes before its time slice has ended it leaves the system

Question 17

Describe the Multi-Level Feedback Queue scheduling algorithm.

Answer 17

Several queues of different priorities with jobs migrating downwards

Question 18

Describe the Shortest Remaining Time scheduling algorithm.

Answer 18

The job with the shortest expected remaining time is put to the front of the queue.

Question 19

Whats an advantage of using Multi Level Feedback Queues for scheduling?

Answer 19

Services most urgent interrupts first

Question 20

Whats a disadvantage of using Multi Level Feedback Queues for scheduling?

Answer 20

Hard to implement

Question 21

Define a real-time operating system.

Answer 21

Perform a task within a guaranteed time frame
Used in systems were a response within a given time frame is critical

Question 22

State the function of the BIOS.

Answer 22

Running tests upon the computer’s startup

Question 23

Name the 3 tests carried out by the BIOS.

Answer 23

Power-On Self Test (POST)
Checking the CPU clock, memory & processor
Testing for external memory devices

Question 24

Describe the function of the POST.

Answer 24

Ensures all hardware is correctly connected & functional

Question 25

What is the role of a device driver?

Answer 25

Enable the operating system to interact with hardware devices

Question 26

Give uses of virtual machines.

Answer 26

Testing programs
Protection from malware
Running software compatible with different version & types of OS

Question 27

What is a virtual machine?

Answer 27

Software that functions like a physical computer only using software resources