Process & Thread (Quick Summary)

1. Process

A Process is a Program that is currently executing in Memory.

• Resource Allocation: Each Process receives its own Memory Space (Isolated). If it crashes, it will not affect other Processes.
• Process Control Block (PCB): A Data Structure used by the OS to store the state of a Process (e.g., State, Program Counter, CPU Registers, Memory Limits).
• States: New -> Ready -> Running -> Waiting/Blocked -> Terminated

2. Thread

A Thread is a sub-unit of processing within a Process.

• Shared Resources: Threads within the same Process share the same Memory Space (Code, Data, Heap) but have their own Stack and Registers.
• Advantages: Creation and Switching consume significantly fewer resources compared to Processes.
• Precautions: Because memory is shared, there is a risk of Race Conditions if Synchronization is not handled properly.

3. Context Switching

The process where the CPU stops executing one Process/Thread to switch to another.

• Mechanism: The OS saves the current state into the PCB (or TCB for Threads) and loads the state of the next item in the queue.
• Overhead: This is a high-cost operation because the CPU is not performing actual Computation during a context switch (Threads have lower overhead than Processes).