🧠 What are Process States?
A process goes through several states in its life cycle — from creation to termination — depending on what it’s doing (waiting, running, blocked, etc.).
The OS maintains and switches these states via a Process Control Block (PCB).
🔁 Common Process States (Modern OSes)
Here’s a simplified 5-state model that covers almost everything FAANG interviews care about:
1. New
-
Process is being created.
-
OS is allocating memory, setting up PCB, etc.
2. Ready
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Process is loaded into memory and waiting to be scheduled on the CPU.
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It’s ready to run but not yet running.
3. Running
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Process is currently executing on the CPU.
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Only one process per core can be in this state at any time.
4. Blocked / Waiting
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Process is waiting for I/O (e.g., disk, network, user input).
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It cannot run until the I/O completes.
5. Terminated / Exit
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Process has completed execution or was killed.
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OS cleans up its memory, I/O, and PCB.
📊 Process State Diagram
+---------+
| New |
+----+----+
↓
+----v----+
| Ready |<----------------------+
+----+----+ |
↓ |
+----v----+ I/O complete |
| Running |------------------>+ |
+----+----+ | |
↓ I/O request | |
+----v----+ | |
| Blocked |-------------------+ |
+----+----+ |
↓ |
+----v----+ |
| Terminated |<------------------+
+-----------+
🧠 Key Transitions Explained
| Transition | Trigger |
|---|---|
| New → Ready | Process is admitted into memory |
| Ready → Running | CPU scheduler picks the process |
| Running → Blocked | Process makes an I/O request |
| Blocked → Ready | I/O completes |
| Running → Ready | Time slice expires (preemption) |
| Running → Terminated | Process exits or is killed |
📦 Modern OS Enhancements (for depth)
| Additional State | Meaning |
|---|---|
| Suspended | Process is swapped out of memory (still in disk) |
| Zombie | Process finished execution, but parent hasn’t read its exit status |
| Orphan | Child process whose parent died (handled by init in Linux) |
These are mostly edge cases, but can be useful in interviews if pushed deeper.
🧠 Interview-Ready One-Liner:
A process transitions through several states — New, Ready, Running, Blocked, and Terminated — based on its interaction with the CPU, memory, and I/O. The OS uses these states to schedule and manage processes efficiently.