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 three functions of an operating system

Answer 2

three from:
memory management
resource management 
i/output managment 
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 a 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 the scheduling algorithms pre-emptive or non pre-emptive ?

Answer 7

pre-emptive : RR , SRT , MLFQ

non-preemptive : FCFS, SJF

Question 8

give one advantage and disadvantage of using multilevel feedback queues for scheduling

Answer 8

advantage: service 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 a 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

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