(Course Code: CS 4001 / CB/IT 4001 – Operating Systems – 4th Semester Polytechnic CS)
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2.1 Process Management
Process management is one of the core functionalities of an operating system. A process is a program in execution. The OS is responsible for handling process creation, scheduling, execution, and termination.
2.1.1 Process Concepts
A process consists of multiple components, including:
Program Code – Contains the executable instructions.
Process Control Block (PCB) – Stores process-related information such as process ID, process state, registers, and scheduling details.
Process States:
New: The process is created but not yet ready for execution.
Ready: The process is waiting for CPU time.
Running: The process is currently executing.
Waiting: The process is waiting for an I/O operation.
Terminated: The process has completed execution.
📌 Diagram of Process States:
New ---> Ready ---> Running ---> Terminated
| |
v v
Waiting <-------> Running 
2.1.2 Operations on Processes
The OS performs the following operations on processes:
Process Creation: A new process is created by the parent process.
Process Termination: The process completes execution or is forcibly terminated.
Process Execution: The process moves through different states during its lifecycle.
Process Scheduling: Determines which process gets CPU time.
2.1.3 Inter-Process Communication (IPC)
Inter-Process Communication (IPC) allows processes to exchange data and synchronize execution.
Types of IPC:
Shared Memory: Processes communicate by accessing the same memory space.
Message Passing: Processes send and receive messages via communication channels.
📌 Example: Shared Memory vs. Message Passing
Process A <---- Shared Memory ----> Process B
Process A <---- Message Queue ----> Process B 
2.2 Process Scheduling
Process scheduling ensures efficient CPU utilization by determining the order in which processes execute.
2.2.1 First-Come, First-Served (FCFS)
Jobs execute in the order of arrival (like a queue).
Non-preemptive scheduling.
Disadvantage – Long waiting times (Convoy Effect).
📌 Example:
Processes: P1 P2 P3
Arrival Time: 0 1 2
Burst Time: 5 3 2
FCFS Execution Order: P1 → P2 → P3 2.2.2 Shortest Job First (SJF)
The process with the shortest execution time runs first.
Can be preemptive or non-preemptive.
Disadvantage – Requires prior knowledge of execution time.
📌 Example:
Processes: P1 P2 P3
Burst Time: 7 2 5
SJF Execution Order: P2 → P3 → P1 2.2.3 Priority Scheduling
Each process is assigned a priority.
Highest priority process executes first.
Can be preemptive or non-preemptive.
📌 Example:
Processes: P1 P2 P3
Priority: 3 1 2
Execution Order: P2 → P3 → P1 2.2.4 Round Robin (RR)
Each process gets a fixed time quantum (e.g., 4ms).
If a process does not finish, it goes to the end of the queue.
📌 Example:
Time Quantum: 4ms
Processes: P1 P2 P3
Burst Time: 5 3 7
Execution Order: P1 → P2 → P3 → P1 → P3 2.3 Multi-Threaded Programming
A thread is a lightweight process that runs within a process.
User Threads – Managed at the user level.
Kernel Threads – Managed by the OS.
Advantages:
✅ Faster context switching
✅ Efficient resource sharing
✅ Parallel execution
2.4 Memory Management
Memory management ensures efficient allocation and deallocation of memory.
2.4.1 Memory Allocation
Static Allocation: Fixed memory at compile time.
Dynamic Allocation: Memory allocated at runtime.
2.4.2 Swapping
Processes move between RAM and disk to free up memory.
Allows more processes to run than available RAM.
📌 Diagram:
+-----------+ +-----------+
| Process A | | Process B |
+-----------+ +-----------+
↕ Swapping
+-----------+ +-----------+
| Process C | | Process D |
+-----------+ +-----------+ 
2.4.3 Paging
Memory is divided into fixed-size pages.
Reduces external fragmentation but may cause page faults.
2.4.4 Segmentation
Memory is divided into variable-sized segments.
Better for handling logical divisions of programs.
2.5 Virtual Memory
Virtual memory allows execution of processes larger than available RAM.
Uses disk as an extension of RAM.
Implements demand paging and swapping.
Enhances multitasking capabilities.
Conclusion
This concludes Unit 2: Process and Memory Management in Operating Systems (CS 4001/CB/IT 4001).
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