CUET PG 2021 — Computer PYQ

Solution aur Logic

Sahi jawab hai: Shortest Job First (SJF).

SJF algorithm isliye sabse behtar maana jata hai kyunki yeh un processes ko pehle execute karta hai jinka execution time (burst time) sabse chota hota hai. Mathematical taur par, jab hum chote numbers ko pehle list karte hain, toh unka "cumulative sum" (jo waiting time banta hai) hamesha minimum aata hai

SJF ke do roop hote hain:

1. Non-preemptive SJF: Ek baar process shuru ho gayi toh khatam hone par hi rukegi.

2. Preemptive SJF (SRTF - Shortest Remaining Time First): Agar koi aur choti process aa jaye, toh current process ruk jati hai. SRTF hi woh algorithm hai jo technically "optimal" minimum waiting time deta hai.

Ek Example ke saath Samjhein

Maan lijiye 3 processes hain: $P1(10ms)$, $P2(3ms)$, $P3(1ms)$.

1. FCFS (First Come First Serve) mein:

• $P1$ wait karega: $0ms$

• $P2$ wait karega: $10ms$

• $P3$ wait karega: $13ms$

  $$\text{AWT}=\frac{0+10+13}{3}=7.66ms$$

2. SJF mein (Shortest Job First):

• $P3$ (1ms) wait karega: $0ms$

• $P2$ (3ms) wait karega: $1ms$

• $P1$ (10ms) wait karega: $4ms$

  $$\text{AWT}=\frac{0+1+4}{3}=1.66ms$$

Yahan hum saaf dekh sakte hain ki:

Comparison Table

Algorithm	Waiting Time	Characteristics
FCFS	High	Simple, lekin "Convoy Effect" hota hai.
SJF / SRTF	Minimum	Optimal, lekin burst time pehle se jaanna mushkil hai.
Round Robin	Moderate	Time sharing ke liye best hai.
Priority	Variable	Important tasks pehle hote hain.

Final Answer: Shortest Job First (SJF)