Question

Describe the various states a process can transition through during its lifecycle. Use a
state transition diagram to illustrate these states and the events that trigger transitions
between them

Answer 1

A process in an operating system goes through various states during its lifecycle. Understanding these states is crucial for efficient process management. Below are the common states a process can transition through:

### Process States

1. **New**: The process is being created.
2. **Ready**: The process is in the ready queue, waiting for CPU time.
3. **Running**: The process is currently being executed by the CPU.
4. **Waiting (Blocked)**: The process is waiting for some event (like I/O completion) to occur.
5. **Terminated (Exit)**: The process has finished execution and is now being removed from the system.

### State Transition Diagram

To illustrate these states and the events that trigger transitions between them, here’s a simple representation of a state transition diagram:

```
+-------+
| New |
+-------+
|
| Create
V
+--------+
| Ready |
+--------+
|
| Scheduler allocates CPU
V
+--------+
| Running |<-------------------
+--------+ |
| |
| I/O request | Timer interrupt
| |
V |
+---------+ |
| Waiting | |
+---------+ |
| |
| I/O completion |
V |
+--------+ |
| Ready |------------------+
+--------+
|
| Scheduler allocates CPU
V
+--------+
| Running |
+--------+
|
| Exit
V
+-----------+
| Terminated|
+-----------+
```

### Description of Transitions

1. **New → Ready**: When a process is created, it transitions from the New state to the Ready state.
2. **Ready → Running**: The process is selected by the scheduler, transitioning it to the Running state.
3. **Running → Waiting**: If the process requires I/O or needs to wait for an event, it will transition to the Waiting state.
4. **Waiting → Ready**: When the I/O or the event the process is waiting for is completed, it moves back to the Ready state.
5. **Running → Ready**: If the process’s time slice expires (due to a timer interrupt), it will move back to the Ready state.
6. **Running → Terminated**: Once a process completes its execution, it transitions to the Terminated state.

#### Notes:
- **Preemption**: A running process may be preempted to allow another process to run, particularly in time-sharing systems.
- **Concurrency**: Many processes may be in the Ready state waiting for execution on the CPU at any given time.

This lifecycle is crucial for managing resources and ensuring efficient process scheduling in an operating system.