Do exercise $2$ not exercise $1$: Consider the processes $P_1$ to $P_5$ with the following service times $d_i,$ arrival times $a_i,$

and priorities $p_i$ :

A single$-$processor$/$single core system is used and the time quantum is $4.$ Visualise

for the scheduling algorithms below the resulting schedules using a Gantt chart and

calculate the average residence time and the average waiting time:

$($a$)$ First Come First Serve $($FCFS$),$

$($b$)$ Shortest Job First $($SJF$),$

$($c$)$ Shortest Remaining Time First $($SRTF$),$

$($d$)$ Round Robin $($RR$),$

$($e$)$ Round Robin with priorities $(R{R}_{\text{p}\text{r}\text{i}\text{o}}).$

$($A note concerning round$-$robin scheduling: as said on the slides, newly arrived processes

are appended to the tail of the ready queue; furthermore, if a new process $($even one

with a higher priority$)$ arrives, another process that has already started its time slice is

allowed to continue.$)$

In the above example it would theoretically be possible that two processes arrive at the

same time $($and then it would not be possible to tell which process came first, e$.$g$.,$ in

case of FCFS$).$ Why can in practise no two processes arrive at the same time $($at least

if only single$-$processor$/$single core systems are considered$)?$ Hint: Think about what

leads to the "arrival" of a process at an operating system and whether such arrivals can

happen at the same time on a single$-$processor$/$single core system$$lease