1.2.1 Systems Software

Question 1

what is an operating system

Answer 1

collection of programs that provide an interface between user & computer

Question 2

what are some functions of an os

Answer 2

resource management, file management, security, interrupt handling, utilities, ui

Question 3

paging

Answer 3

available memory is split into fixed sizes called pages
each page has a memory address
pages move in/out of secondary storage as needed
pages do not have to be stored contiguously

Question 4

segmentation

Answer 4

available memory split into variable sizes, logically, called segments
more space efficient

Question 5

virtual memory

Answer 5

if main memory is full, then seconday storage is used instead
this can cause disk thrashing => computer slows down/freezes due to pages being swapped regularly between ram/secondary storage

Question 6

interrupt definition

Answer 6

a signal to the processor indicating that a device/process needs attention

Question 7

interrupt process

Answer 7

1. the processor checks the interrupt register at the end of the FDE cycle
2. if there is an interrupt with higher priority, then the current contents of the register are transferred into a stack
3. The relevant ISR is loaded
4. if no more interrupts w/ higher prioroty then the stack is popped bacl into registers
5. FDE resumes

Question 8

round robin

Answer 8

each job allocated an equal share of processing time
adv: all processes will eventually complete
dis: does not take into account different prioroties, choosing the correct time slice is difficult

Question 9

first-come-first-served

Answer 9

processes are completed in the order they arrive
adv: easy to implement
dis: large processes will take up all of the CPUs time

Question 10

multi level feedback queue

Answer 10

processes organised into different queues w/ different priorities. jobs can be swapped between queues
dis: jobs w/ lower prioroties may never complete

Question 11

shortest job first/shortest time remaining

Answer 11

(user estimates execution time), smallest execution is 1st
dis: longer jobs may never complete

Question 12

bios (basic input output system)

Answer 12

• first program to load up when the device is switched on after POST test
• stored in ROM, loads OS into RAM

Question 13

device drivers

Answer 13

• software that allows for os to communicate w/ external hardware eg keyboard, mic, speakers

Question 14

virtual machine

Answer 14

• software implementation to emulate a computer
• partitions the hardware into multiple computers

Question 15

distributed os

Answer 15

• runs across multiple devices & appears as a single unit
• can use the computing power of all devices

Question 16

embedded os

Answer 16

• os w/ specialised functions
• system software
• stored in rom
• used in most household devices

Question 17

multi-tasking os

Answer 17

• seemingly allows for multiple tasks to happen simeltaneously/concurrently
• uses scheduling algorithms

Question 18

multi-user os

Answer 18

allows for multiple users to log in and complete independent tasks at the same time

Question 19

real time os

Answer 19

• designed for immediate data processing
• operates in real time