Core CS

Process Concept

A process is simply a computer program currently in execution. While a program sitting on a hard drive is passive, like a recipe in a book, a process is active—it is the computer actively reading the instructions, using memory, and utilizing the CPU to carry out tasks.

<h2>Definition A process is the fundamental unit of work in a modern operating system. It consists of more than just the source code; it represents an entire execution environment loaded into the system's main memory (RAM). When an executable file (like a browser, text editor, or background service) is launched, the operating system allocates dedicated memory and resources to turn that static file into an active, running process managed by a data structure called the Process Control Block (PCB).In memory, a process is structured into four primary sections:<ul><li>Text Section: The compiled machine code instructions being executed.</li><li>Data Section: Global and static variables allocated before program startup.</li><li>Heap: Dynamically allocated memory requested during runtime (e.g., using <code>malloc</code> in C or <code>new</code> in Java/C++).</li><li>Stack: Temporary memory storing local variables, function parameters, and return addresses.</li></ul>Key Features of a Process<ul><li>Dynamic Nature: Unlike static files, a process constantly changes its internal values, registers, and operational state over time.</li><li>Isolated Address Space: Operating systems assign each process its own virtual memory boundary, preventing one process from accidentally corrupting or crashing another.</li><li>Resource Allocation: Every process receives and tracks its own set of system resources, including CPU time slices, open files, network sockets, and I/O devices.</li><li>Identifiable Tracking: Each process is assigned a unique integer identifier called a PID (Process ID) that the OS uses for monitoring, scheduling, and termination.</li><li>Process Control Block (PCB): The OS maintains a dedicated record per process containing the Program Counter, CPU registers, scheduling priority, and memory management limits.</li></ul>States of a ProcessDuring its lifecycle from startup to shutdown, a process moves through five standard states:<ol><li>New (Created): The initial stage where the process is being created and its program code is being read from disk, but it has not yet been loaded into main memory.</li><li>Ready: The process is fully loaded in main memory and ready to run, simply waiting in a queue for the CPU scheduler to allocate CPU time.</li><li>Running: The CPU is actively executing the process's instructions. In a single-core system, only one process can be in this state at any instant.</li><li>Waiting (Blocked): The process cannot continue executing until an external event occurs, such as waiting for keyboard input, disk read/write, or network data.</li><li>Terminated (Exit): The process has finished its execution or was halted due to an error, and the OS is releasing its assigned resources and memory.</li></ol>Process State TransitionsProcesses shift between states based on CPU scheduling, hardware interrupts, and system calls: <img src="uploads/tutorials/2026/09/tutorial-20260914-225234-c7ddb1299f2c.png" alt="ChatGPT Image Sep 14, 2026, 10_48_54 PM"> </h2>