1.2.1 Systems Software

Question 1

what is os

Answer 1

operating system:
-boot loader from ROM loads OS into RAM
-manages hardware and provide interface and application software

Question 2

the need of os

Answer 2

provide interface
control access
control hardware(peripheral management)
act as a platform which application can be run

Question 3

function of os

Answer 3

-UI
-memory management
-interrupt handling
-processor scheduling

Question 4

memory management

Answer 4

paging and segmentation

-os needs to manage the allocation of main memory (RAM) for the programs

Question 5

paging

Answer 5

memory split into fixed size

-pages are memory divided into fixed size chunks
-each page have an address
-pages can be used by programs and processes
-page table maps the logical memory location and physical memory location

disadvantage: takes no account of how it splits the program-> pages will not be contiguous in physical terms

Question 6

segmentation

Answer 6

memory split into different lengths

-segments are memory divided into different lengths
-could store a part of program (e.g. particular function/subroutine)

Question 7

virtual memory

Answer 7

when some of the pages currently open but not actively in used are temporarily swapped and allocated into secondary storage

problem: disk thrashing
-> as main memory fills up and pages are constantly swapping with virtual memory→ computer gets slower

Question 8

interrupts

Answer 8

sending a signal to the cpu to raise awareness

examples:
-I/O devices sends interrupt signal
-printer out of paper
-error in program
-power failure
-scheduled interrupt(e.g. updates)

Question 9

role of ISR

Answer 9

mini program to repsond to interrupt request

Question 10

role of interrupt and ISR within FDE cycle

Answer 10

interrupts are checked at the end of each clock cycle
ISR kicks in if needed
- pushing current contents of its registers into a stack
- popped from stack and reloaded into CPU once interrupt process is finished

Question 11

purpose of processor scheduling

Answer 11

-one cpu process instruction for one application at a time
-os need to schedule when application to use cpu
- illusion of multi-tasking/ applications running simultaneously

Question 12

aim of processor scheduling

Answer 12

• give reasonable run time
• maximise the use of time in CPU
• fairness on a multi-user system

Question 13

process of scheduling

Answer 13

• new process enters the ready queue
• moves onto running state when the previous process is executed/ blocked
• three outcomes after the running state:
  
  • completely finish the execution AND leave the system
  • blocked : require input/output to finish or continue the process
  • run out of time → process suspended and goes back to the ready queue

Question 14

scheduling algorithm

Answer 14

round robin
FCFS
SJF
STR
multi-level feedback queue

Question 15

round robin (RR)

Answer 15

• system clock slices the task
• each process is allocated a fixed amount of time/time slice (by FIFO)
• if the process is not completed by the end of time slice, it returns to the back of ready queue AND the next job is allocated a time slice

Question 16

first come first served

Answer 16

• processes executed in the order they arrive
• like a supermarket queue

Question 17

shortest time remaining

Answer 17

• pre-emptive: process can be suspended when a process of higher priority jumps in
• the suspended process goes to the back of the queue
• if the suspended process had the smallest run time in the queue, it would be run again

Question 18

shortest job first

Answer 18

• aka shortest process next
• the process of their job is run until they finish
• scheduler needs to know how long each process will take

Question 19

multi-level feedback queue

Answer 19

• multiple queues are created with different priority queue
• jobs uses too much cpu time will be moved to lower priority queue
• jobs waited for a long time can be moved to a higher priority

advantage: allows flexibility

disadvantage: complex and abstract

suitability: when system has more than one processor/processor core, that can handle more than one process queue at a time

Question 20

types of os

Answer 20

distributed
embedded
multi-user
multi-tasking
real time

Question 21

distributed os

Answer 21

using the processing power of multiple computers across a network for one single task

Question 22

embedded os

Answer 22

• run on dedicated hardware- for max efficiency with low-powered processors(not cpu) and little memory
  
  • applications programs held in ROM
  • limited RAM
  • simple and minimal user interface

Question 23

multi-tasking os

Answer 23

• a single processor appear to do more than one task simultaneously by scheduling processor time
  
  • e.g. computers handling more than one application

Question 24

multi-user os

Answer 24

handle request of multiple people using different computers on a network at the same time

Question 25

real time os

Answer 25

real time: system gives a response within a guaranteed time frame - operates in safety critical environment - execute within a known time frame - must be failsafe e.g. monitoring machines in hospitals

Question 26

what is BIOS

Answer 26

- stored in ROM - test all hardware/components (for POST- power on self-test) - boot up OS into RAM

Question 27

device drivers

Answer 27

what is it: - software that tells os to communicate with devices (like mouse, keyboard and printer)//OR// program that provides interface for OS to interact with a device - drivers are hardware dependent and OS specific how does it work: -translates instructions of os to device (e.g. it ensures word documents to be printed the same from any printer)

Question 28

virtual machines

Answer 28

any instance where software is used to take the function of a machine including executing intermediate code or running an os within another - e.g. connect to the school network like a school computer with personal device (remote desktop) - Cloud computing is NOT virtualisation but virtual machines.