What are the different states of a Process?

A process is an active program under execution. It includes the program counter, process stack, registers, and program code, making it more comprehensive than just the static program code (text section).

A process passes through different states during its execution lifecycle. While these states may vary across operating systems, the fundamental process states are standardized. The diagram below illustrates the common process states and their transitions −

New

This is the initial state when a process has just been created. The process exists but has not yet been admitted to the pool of executable processes by the operating system. The process control block (PCB) is created and initialized.

Ready

In the ready state, the process is waiting to be assigned to the processor by the short-term scheduler. The process has all necessary resources except the CPU and is ready for execution. Multiple processes can be in the ready state simultaneously, forming a ready queue.

Running

The process is in the running state when its instructions are being executed by the processor. Only one process can be in the running state at any given time on a single-core system. The process transitions from ready to running via dispatcher.

Blocked (Waiting)

The process enters the blocked state when it is waiting for some event to occur, such as I/O completion, resource availability, or a signal from another process. The process cannot continue execution until the awaited event occurs.

Ready Suspended

Processes in this state are stored in secondary memory due to memory shortage. They were initially in the ready state but were swapped out to make room for other processes. These processes can be activated back to the ready state when memory becomes available.

Blocked Suspended

Similar to ready suspended, these processes are in secondary memory but were originally in the blocked state. They were swapped out while waiting for an event. A process can transition from blocked suspended to ready suspended when the awaited event occurs.

Terminated

The process reaches the terminated state when it has finished execution or has been killed by the operating system. The process is removed from main memory, and its PCB is deleted, freeing up system resources.

Conclusion

Process states represent the different phases in a process's lifecycle, from creation to termination. Understanding these states is crucial for process management, scheduling algorithms, and system resource allocation. The state transitions are controlled by the operating system's scheduler and system events.