Process Life Cycle States and Transition Diagram in Operating Systems

A process in an operating system does not execute in one uninterrupted stretch. Instead, it moves through a set of well-defined states from creation to completion. The classic five-state model includes New, Ready, Running, Waiting/Blocked, and Terminated.3

The purpose of a transition diagram is to show both:

1. the possible states of a process, and
2. the events that cause movement from one state to another, such as scheduling, preemption, I/O wait, and completion.2

A process typically enters the system when it is created, waits in a ready queue for CPU service, executes when scheduled, may pause for I/O or another event, and eventually exits.2 In a single-processor system, at most one process is in the Running state at a time, while many may be in Ready or Waiting queues.2

The standard transition diagram is:

This model is fundamental to understanding CPU scheduling and context switching, because every scheduling decision depends on the current state of each process.2

Footnotes

1. States of a Process in Operating Systems - GeeksforGeeks - Overview of the five main states and standard transitions. ↩ ↩² ↩³

2. 5 State Process Model in Operating System - GeeksforGeeks - Describes the five-state model and common state changes. ↩ ↩²

3. Chapter 3: Processes (Operating System Concepts, 10th Edition slides) - Defines process states, transition diagrams, queues, and context switching. ↩ ↩² ↩³ ↩⁴

4. Understanding Process States in Operating Systems - Summarizes the reasons for transitions among ready, running, waiting, and terminated states. ↩ ↩²

The Five Main Process States

1. New

The New state represents a process that has just been created. At this point, the OS has recognized the program as a process and begins preparing its internal representation, usually including a PCB.2 The process is not yet executing; it must first be admitted to main memory and the ready queue.2

2. Ready

A process in the Ready state has everything needed to execute except the CPU itself.2 It is loaded or admitted for execution and waits in the ready queue until the scheduler selects it. Multiple processes may be ready simultaneously.2

3. Running

A process is Running when the CPU is actively executing its instructions.2 In a single-core system, only one process can occupy this state at any instant. While running, the process may finish, be preempted, or request an operation that forces it to wait.2

4. Waiting / Blocked

A process enters the Waiting or Blocked state when it cannot continue until some event occurs, most commonly I/O completion, user input, inter-process signaling, or resource availability.3 This distinction is important: a ready process is able to run but lacks the CPU, whereas a blocked process cannot run even if the CPU is free.2

5. Terminated

The Terminated state marks the end of the process life cycle. The process has either completed successfully or has been aborted by the OS or another entity.2 Its resources are released, and its PCB is eventually removed.

A useful conceptual summary is shown below:

3

Footnotes

1. States of a Process in Operating Systems - GeeksforGeeks - Overview of the five main states and standard transitions. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. Chapter 3: Processes (Operating System Concepts, 10th Edition slides) - Defines process states, transition diagrams, queues, and context switching. ↩ ↩² ↩³ ↩⁴ ↩⁵

3. 5 State Process Model in Operating System - GeeksforGeeks - Describes the five-state model and common state changes. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

4. Understanding Process States in Operating Systems - Summarizes the reasons for transitions among ready, running, waiting, and terminated states. ↩ ↩² ↩³ ↩⁴

Interpreting the Transition Diagram

The transition arrows represent operating-system events rather than arbitrary movements. The most important transitions are:

• New $\rightarrow$ Ready: the process is admitted after creation.2
• Ready $\rightarrow$ Running: the scheduler dispatches the process to the CPU.2
• Running $\rightarrow$ Waiting: the process requests I/O or must wait for an event.2
• Waiting $\rightarrow$ Ready: the event completes and the process becomes runnable again.2
• Running $\rightarrow$ Ready: preemption occurs because the time quantum expires or a higher-priority process arrives.2
• Running $\rightarrow$ Terminated: execution ends or the process is killed.2

The diagram can also be understood as a resource-eligibility model:

• Ready means eligible for CPU.
• Running means currently using CPU.
• Waiting means temporarily ineligible due to an unsatisfied event condition.2

A more detailed conceptual flow is:

This explains why processes may cycle repeatedly among Ready, Running, and Waiting many times, but normally enter New once and Terminated once.

Footnotes

1. Chapter 3: Processes (Operating System Concepts, 10th Edition slides) - Defines process states, transition diagrams, queues, and context switching. ↩ ↩² ↩³ ↩⁴

2. States of a Process in Operating Systems - GeeksforGeeks - Overview of the five main states and standard transitions. ↩ ↩² ↩³ ↩⁴

3. Understanding Process States in Operating Systems - Summarizes the reasons for transitions among ready, running, waiting, and terminated states. ↩ ↩² ↩³ ↩⁴

4. 5 State Process Model in Operating System - GeeksforGeeks - Describes the five-state model and common state changes. ↩ ↩² ↩³ ↩⁴

Extended Process States: Suspended Variants

Many modern descriptions go beyond the basic five-state model and add suspended states:

• Ready Suspend
• Blocked Suspend2

These appear when the OS removes a process from main memory, usually to manage limited RAM through swapping. A blocked process may be moved to Blocked Suspend if it is waiting for an event and is not immediately useful in memory. If the event later occurs while it is still swapped out, it may become Ready Suspend until it is brought back into memory.2

This extended model is especially useful when discussing swapping and medium-term scheduling.2 However, for most introductory explanations of the process life cycle, the five-state diagram remains the primary model.2

Footnotes

1. Process Suspension and Process Switching - TutorialsPoint - Explains suspended states and memory-related swapping behavior. ↩ ↩² ↩³ ↩⁴

2. Lecture 05 Chapter 3: Process Concepts PDF - Shows the seven-state model with Ready Suspend and Blocked Suspend transitions. ↩ ↩² ↩³

3. States of a Process in Operating Systems - GeeksforGeeks - Overview of the five main states and standard transitions. ↩

4. Chapter 3: Processes (Operating System Concepts, 10th Edition slides) - Defines process states, transition diagrams, queues, and context switching. ↩

The chart above is a conceptual learning aid, not a universal measurement. In many interactive and multiprogrammed systems, transitions related to I/O waiting and event completion occur very frequently because processes often alternate between CPU bursts and I/O bursts.2 By contrast, termination occurs only once per process.

From a scheduling perspective, the three most active operational states are:

• Ready
• Running
• Waiting2

The OS constantly moves processes among these states to maximize CPU utilization and system responsiveness.2 This is why process-state diagrams are central not only to process management but also to queueing, scheduling, and context-switch analysis.2

Mathematically, if a process alternates between CPU bursts and I/O waits, its lifetime can be viewed as a sequence of transitions:

$$\text{New} \rightarrow \text{Ready} \rightarrow (\text{Running} \leftrightarrow \text{Waiting} \leftrightarrow \text{Ready})^k \rightarrow \text{Terminated}$$

where $k \geq 0$ denotes the number of repeated execution-wait cycles.2

Footnotes

1. States of a Process in Operating Systems - GeeksforGeeks - Overview of the five main states and standard transitions. ↩ ↩² ↩³

2. Understanding Process States in Operating Systems - Summarizes the reasons for transitions among ready, running, waiting, and terminated states. ↩ ↩² ↩³ ↩⁴

3. 5 State Process Model in Operating System - GeeksforGeeks - Describes the five-state model and common state changes. ↩

4. Chapter 3: Processes (Operating System Concepts, 10th Edition slides) - Defines process states, transition diagrams, queues, and context switching. ↩ ↩²

5. Process Suspension and Process Switching - TutorialsPoint - Explains suspended states and memory-related swapping behavior. ↩

Final Conceptual Summary

The life cycle of a process is best understood as a controlled progression through states managed by the operating system.2 The transition diagram shows not only where a process can be, but also why it moves:

• creation leads to New,
• admission leads to Ready,
• CPU allocation leads to Running,
• I/O or event dependency leads to Waiting,
• completion leads to Terminated.3

The most important insight is that process management is dynamic. A process may repeatedly alternate between Ready, Running, and Waiting, depending on scheduling and external events.2 This dynamic behavior is what allows a multiprogramming operating system to keep the CPU busy, overlap computation with I/O, and manage many tasks efficiently.2

Footnotes

1. States of a Process in Operating Systems - GeeksforGeeks - Overview of the five main states and standard transitions. ↩ ↩²

2. Chapter 3: Processes (Operating System Concepts, 10th Edition slides) - Defines process states, transition diagrams, queues, and context switching. ↩

3. 5 State Process Model in Operating System - GeeksforGeeks - Describes the five-state model and common state changes. ↩ ↩²

4. Understanding Process States in Operating Systems - Summarizes the reasons for transitions among ready, running, waiting, and terminated states. ↩ ↩² ↩³

5. Process Suspension and Process Switching - TutorialsPoint - Explains suspended states and memory-related swapping behavior. ↩