First-Come, First-Served (FCFS) Scheduling Algorithm

Explanation

Here is an explanation of the FCFS scheduling program:

1. Purpose

This program simulates the First-Come, First-Served (FCFS) CPU scheduling algorithm (assuming all processes arrive at time 0). It calculates the Waiting Time (WT) and Turnaround Time (TAT) for each process, along with their overall averages.

2. Key Concepts

• Input Parsing: Using split(',') and map(int, ...) to convert a comma-separated string into a list of integers.
• List Initialization: Using [0] * n to pre-allocate lists of a fixed size.
• Cumulative Sums: Iterating with range() to accumulate burst times sequentially.
• Built-in Functions: Using sum() and len()/n to calculate averages.

3. Code Walkthrough

1. Input & Initialization (lines 1–4):

   • Prompts the user for process count (n) and their CPU burst times (bt).
   • Initializes two lists, wt (waiting time) and tat (turnaround time), with zeros.

2. Calculate Waiting Time (lines 5–6):

   • The first process always waits 0 units.
   • Each subsequent process $i$ waits for the time the previous process spent waiting plus its burst time:
     $$\text{WT}[i] = \text{WT}[i-1] + \text{BT}[i-1]$$

3. Calculate Turnaround Time (lines 7–8):

   • Total time spent from arrival to completion:
     $$\text{TAT}[i] = \text{WT}[i] + \text{BT}[i]$$

4. Display Results (lines 9–14):

   • Prints a tab-delimited (\t) table listing Process ID, Burst Time, Waiting Time, and Turnaround Time.
   • Uses sum(wt)/n and sum(tat)/n to display the average WT and TAT.

4. Output

Example Run:

Enter number of processes: 3
Enter burst times separated by comma ',': 4,3,2
P	bt	wt	tat
1 	 4 	 0 	 4
2 	 3 	 4 	 7
3 	 2 	 7 	 9
Avg WT = 3.6666666666666665
Avg TAT = 6.666666666666667