Consider the process details given in the following table. A new pre-emptive…

Concept. LRTN (Longest Remaining Time Next) is the pre-emptive counterpart of Longest Job First: at every clock tick the scheduler compares the remaining burst time of every ready (arrived, unfinished) process and runs whichever one currently has the

largest remaining burst time. Because every process's remaining time keeps shrinking as it executes, this comparison must be redone at every time unit — not only when a process arrives or completes — so the process holding the CPU can change even between arrivals. When two or more ready processes tie on remaining time, the tie is broken in favour of the process with the better (numerically smaller) priority value — the question fixes the priority order as 1 > 2 > 3 > 4.

Application. The given process data is:

Tracing every arrival/completion decision point unit by unit (re-checking the tie-break rule whenever two or more remaining times are equal) gives this pre-emptive schedule:

Reading the completion time (CT) of each process off that trace:

Where TAT = CT − AT, WT = TAT − BT, and RT = (time of the process' first CPU allocation) − AT.

• Turnaround time of P2 = CT(P2) − AT(P2) = 24 − 4 = 20

• Response time of P3 = (P3's first execution slot, 6) − AT(P3) = 6 − 3 = 3

Cross-check. P0 is already ready at t = 0 and every process is CPU-hungry, so the schedule never idles; the last process finishes at t = 25, which equals the sum of all four burst times (3 + 9 + 7 + 6 = 25) — confirming every time unit in the trace above is accounted for exactly once.