2. PROCESS MANAGEMENT

2.2. Process States Life Cycle

Process States 

When a process executes, it goes through various states. While names and number of states might slightly vary in different operating systems, here are the five common states:

 No. State What It Means
1️⃣ Start Process is created for the first time.
2️⃣ Ready Process is waiting for CPU to be assigned by the OS scheduler.
3️⃣ Running Process is currently using the CPU and being executed.
4️⃣ Waiting Process is waiting for some resource (e.g., user input, file, device).
5️⃣ Terminated Process has finished execution or is killed; it will be removed from memory.

State Transitions (Example):

  • Start → Ready → Running → Waiting/Ready → Running → Terminated

Process Control Block (PCB)

A PCB is like a file or record that the Operating System keeps to track every process. It stores everything the OS needs to manage and switch between processes.

 No. Field What It Stores
1️⃣ Process State Current state: Ready, Running, Waiting, etc.
2️⃣ Process Privileges What the process is allowed to access (e.g., memory, devices).
3️⃣ Process ID (PID) A unique number to identify each process.
4️⃣ Pointer Link to the parent or related processes.
5️⃣ Program Counter (PC) The address of the next instruction to be executed.
6️⃣ CPU Registers Data stored in CPU registers (saved during context switching).
7️⃣ CPU Scheduling Info Priority, queue pointers, scheduling info.
8️⃣ Memory Info Details like page table, memory limits, segment table.
9️⃣ Accounting Info CPU time used, process start time, user ID, etc.
🔟 I/O Status Info List of I/O devices used, files opened, etc.

 Note:

  • The structure of the PCB depends on the operating system.

  • It’s essential for multitasking because it helps the OS switch between processes.

Process State Diagram

pcb