$($c$)$ Two processes, $Pa$ and $Pb,$ have the following sequential execution patterns:

I$/$O $2ms$; CPU $4ms]$

Pb: $[$CPU $1ms$;$\frac{\text{I}}{O}2ms$ CPU $1ms$ I$/$O $2ms$ CPU $1ms$ I$/$O $2ms$;

CPU $1ms$

I$/$O operations for the two processes do not interfere with each other and

are blocking.

i$.$ If the processes are run consecutively one after another, what is the

elapsed time for all to complete?

ii$.$ Sketch the execution pattern under non$-$preemptive scheduling and de$-$

termine the total elapsed time for completion. You may assume that

processes are scheduled in the order in which they become ready to run

and that in the event of a tie $Pa$ has priority over $Pb.$ You may further

assume that the scheduler and context switches take negligible time.

$[2$ marks$]$