Process States

Five-State Model

        ┌─────────────────────────────────────┐
        │                                     │
        ↓                                     │
     ┌─────┐  admitted   ┌───────┐  dispatch  ┌─────────┐
 New │     │ ──────────→ │ Ready │ ─────────→ │ Running │
     └─────┘             └───────┘            └─────────┘
                           ↑                     │   │
                           │    interrupt/       │   │
                           │    preempt          │   │
                           └─────────────────────┘   │
                                                     │
                         ┌─────────┐   I/O done     │ I/O wait
                         │ Waiting │ ←──────────────┘
                         └─────────┘
                              │
                              │ exit
                              ↓
                         ┌────────────┐
                         │ Terminated │
                         └────────────┘

State Descriptions

State	Description
New	Process is being created
Ready	Waiting to be assigned to CPU
Running	Instructions being executed
Waiting	Waiting for I/O or event
Terminated	Process has finished execution

Context Switch

When CPU switches from one process to another:

1. Save state of current process (to its PCB)
2. Load state of new process (from its PCB)
3. Resume new process execution

Context switch time is overhead (typically 1-1000 microseconds)