$($c$)$ Four processes, $Pa,Pb,Pc,$ and $Pd,$ have the following sequential execution

patterns:

$]$

; CPU $3ms]$

$Pc$ : $[$CPU $1ms$; I$/$O $2ms$; CPU $1ms$; I$/$O $2ms$; CPU $1ms$; I$/$O $2ms$; CPU $1ms]$

$Pd$:$[CPU3ms$;$\frac{\text{I}}{O}3ms$;CPU$3ms]$

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?

$[2$ marks$]$

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

termine the total elapsed time for completion. All processes arrive at

the same time. 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 $Pb,Pc,$ and $Pd$;

$Pb$ has priority over $Pc$ and $Pd$; while

$Pc$ has priority over $Pd.$

You may further assume that the scheduler algorithm and the context

switching take negligible time.

$[2$ marks$]$