Process Table and Process Control Block (PCB) Last Updated : 28 Jul, 2025 Comments Improve Suggest changes Like Article Like Report While creating a process, the operating system performs several operations. To identify the processes, it assigns a process identification number (PID) to each process. As the operating system supports multi-programming, it needs to keep track of all the processes. For this task, the process control block (PCB) is used to track the process’s execution status. Each block of memory contains information about the process state, program counter, stack pointer, status of opened files, scheduling algorithms, etc. All this information is required and must be saved when the process is switched from one state to another. When the process makes a transition from one state to another, the operating system must update information in the process’s PCB. A Process Control Block (PCB) contains information about the process, i.e. registers, quantum, priority, etc. The Process Table is an array of PCBs, which logically contains a PCB for all of the current processes in the system. Structure of the Process Control BlockA Process Control Block (PCB) is a data structure used by the operating system to manage information about a process. The process control keeps track of many important pieces of information needed to manage processes efficiently. The diagram helps explain some of these key data items. Process Control BlockPointer: It is a stack pointer that is required to be saved when the process is switched from one state to another to retain the current position of the process. Process state: It stores the respective state of the process. Process number: Every process is assigned a unique id known as process ID or PID which stores the process identifier. Program counter: Program Counter stores the counter, which contains the address of the next instruction that is to be executed for the process. Register: Registers in the PCB, it is a data structure. When a processes is running and it's time slice expires, the current value of process specific registers would be stored in the PCB and the process would be swapped out. When the process is scheduled to be run, the register values is read from the PCB and written to the CPU registers. This is the main purpose of the registers in the PCB. Memory limits: This field contains the information about memory management system used by the operating system. This may include page tables, segment tables, etc. List of Open files: This information includes the list of files opened for a process. Advantages of Process Control Block (PCB)1. Stores Process DetailsHolds vital data like process ID, process state, program counter, CPU registers, memory limits, etc.Acts as the identity card of the process within the OS.2. Helps Resume ProcessesDuring context switching, the PCB stores the exact execution point and environment.Allows the process to resume seamlessly without restarting.3. Ensures Smooth ExecutionKeeps track of everything a process needs (CPU state, memory, files, devices).Enables the OS to manage processes systematically and without disruption.4. Facilitates Context SwitchingPCB is used to save and restore the state of processes when switching between them.Ensures efficiency in multitasking and responsiveness in real-time systems.5. Aids in SchedulingStores priority, scheduling policy and time slice information.Helps the scheduler decide which process to run next.6. Manages Resource AllocationKeeps records of open files, I/O devices, allocated memory per process.Enables effective resource tracking and avoidance of conflicts.Disadvantages of Process Control Block (PCB)Uses More Memory : Each process needs its own PCB, so having many processes can consume a lot of memory. Slows Context Switching : During context switching , the system has to update the PCB of the old process and load the PCB of the new one, which takes time and affects performance. Security Risks : If the PCB is not well-protected, someone could access or modify it, causing security problems for processes. Additional Points to Consider for Process Control Block (PCB) Interrupt Handling: The PCB also contains information about the interrupts that a process may have generated and how they were handled by the operating system. Context Switching: The process of switching from one process to another is called context switching. The PCB plays a crucial role in context switching by saving the state of the current process and restoring the state of the next process. Real-Time Systems: Real-time operating systems may require additional information in the PCB, such as deadlines and priorities, to ensure that time-critical processes are executed in a timely manner. Virtual Memory Management: The PCB may contain information about a process virtual memory management, such as page tables and page fault handling. Fault Tolerance: Some operating systems may use multiple copies of the PCB to provide fault tolerance in case of hardware failures or software errors. The Process Control Block (PCB) is stored in a special part of memory that normal users can't access. This is because it holds important information about the process. Some operating systems place the PCB at the start of the kernel stack for the process, as this is a safe and secure spot. Process TableA process table is a data structure maintained by the operating system to keep track of all active processes. It contains an entry for each process, known as the Process Control Block (PCB), which stores essential information like process ID, state, program counter, CPU registers, memory usage and resource allocations. The process table helps the OS efficiently manage, schedule and switch between processes. It plays a crucial role in multitasking, ensuring that each process runs smoothly without interference.Advantages of Process Table1. Keeps Track of ProcessesStores essential info like Process ID (PID), state (Running, Waiting, Ready, Terminated), program counter and more.Helps the OS manage multiple processes concurrently.2. Helps in SchedulingContains priority levels, CPU burst times and arrival times.Assists the CPU scheduler in selecting the best process to run next.3. Easy Process ManagementCentralized structure to create, suspend, resume or terminate processes.Enables features like multitasking and context switching.4. Facilitates Context SwitchingStores CPU registers, stack pointers and other context-related data.Ensures smooth transition between processes during preemption or interrupts.5. Enables Inter-Process Communication (IPC)Includes pointers or flags related to shared memory, pipes or message queues.Helps in synchronization and communication between processes.6. Supports Resource AllocationTracks allocated resources (memory, files, I/O devices) per process.Prevents conflicts and ensures fair distribution.7. Essential for Process Synchronization and Deadlock HandlingMaintains info like locks held/requested.Helps the OS detect and handle deadlocks or race conditions.8. Security and Access ControlContains user ID, group ID, permission levels, etc.Enforces process-level access controls and restrictions.9. Debugging and MonitoringUsed by monitoring tools (like top, ps) to display process info.Helps in performance tuning and debugging applications.Disadvantages of Process TableTakes Up Memory : The process table needs space to store information about all processes, which can use a lot of memory in systems with many processes. Slower Operations : When there are too many processes, searching or updating the table can take more time, slowing down the system. Extra Work for the System : The operating system has to constantly update the process table, which adds extra work and can reduce overall system performance. The Process Table keeps a list of all active processes and the PCB holds details about each process. The PCB enables smooth process switching, effective multitasking and efficient resource allocation. Process Control Block in Operating System Visit Course Comment More infoAdvertise with us Next Article What is an Operating System? 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The term was defined by David Patterson, Ga 15 min read PracticeLast Minute Notes – Operating SystemsAn Operating System (OS) is a system software that manages computer hardware, software resources, and provides common services for computer programs. It acts as an interface between the user and the computer hardware.Table of Content Types of Operating System (OS): ThreadsProcessCPU Scheduling Algor 15+ min read Operating System Interview QuestionsAn operating system acts as a GUI between the user and the computer system. In other words, an OS acts as an intermediary between the user and the computer hardware, managing resources such as memory, processing power, and input/output operations. Here some examples of popular operating systems incl 15+ min read Operating Systems - GATE CSE Previous Year QuestionsThe Operating System(OS) subject has high importance in GATE CSE exam because:large number of questions nearly 10-12% of the total asked significant weightage (9-11 marks) across multiple years which can also be seen in the below given table:YearApprox. Marks from OSNumber of QuestionsDifficulty Lev 2 min read Like