Algorithm Overview

FCFS is the simplest scheduling algorithm where the process that arrives first is scheduled first. It follows a straightforward principle: processes are executed in the order of their arrival times.

Example Problem Setup

Consider five processes with the following specifications:

Note: Burst time represents the total CPU time required by each process.

Key Characteristics

Non-preemptive Nature

FCFS is non-preemptive, meaning once CPU is assigned to a process, it cannot be taken back until the process completes or voluntarily gives up the CPU.

Important Clarification: Even though FCFS is non-preemptive, it's not the same as batch processing because:

• We're discussing multiprogramming systems
• Only processes in the ready queue are considered
• Processes can still move to waiting state for I/O operations

Gantt Chart Construction

The execution timeline follows arrival order:

----------------------------------------------------------------
|  P0  |     P1     |   P2   |      P3      |        P4        |
----------------------------------------------------------------
0      2            8        12             21                 33

Execution Details:

• P0: Runs from time 0 to 2 (2 units)
• P1: Runs from time 2 to 8 (6 units)
• P2: Runs from time 8 to 12 (4 units)