Process Control Block in OS

A Process Control Block (PCB) is a data structure that is used by an Operating System to manage and regulate how processes are carried out. In operating systems, managing the process and scheduling them properly play the most significant role in the efficient usage of memory and other system resources. In the process control block, all the details regarding the process corresponding to it like its current status, its program counter, its memory use, its open files, and details about CPU scheduling are stored.

PCB

With the creation of a process, a PCB is created which controls how that process is being carried out. The PCB is created with the aim of helping the OS to manage the enormous amounts of tasks that are being carried out in the system. PCB is helpful in doing that as it helps the OS to actively monitor the process and redirect system resources to each process accordingly. The OS creates a PCB for every process which is created, and it contains all the important information about the process. All this information is afterward used by the OS to manage processes and run them efficiently.

Primary Terminologies Related to Process Control Block

These are also the basic key components of the Process Control Block:

• Process State: The state of the process is stored in the PCB which helps to manage the processes and schedule them. There are different states for a process which are “running,” “waiting,” “ready,” or “terminated.”
• Process ID: The OS assigns a unique identifier to every process as soon as it is created which is known as Process ID, this helps to distinguish between processes.
• Program Counter: While running processes when the context switch occurs the last instruction to be executed is stored in the program counter which helps in resuming the execution of the process from where it left off.
• CPU Registers: The CPU registers of the process helps to restore the state of the process so the PCB stores a copy of them.
• Memory Information: The information like the base address or total memory allocated to a process is stored in PCB which helps in efficient memory allocation to the processes.
• Process Scheduling Information: The priority of the processes or the algorithm of scheduling is stored in the PCB to help in making scheduling decisions of the OS.
• Accounting Information: The information such as CPU time, memory usage, etc helps the OS to monitor the performance of the process.

There can be more information about a process that can be stored in the PCB.

Operations that are Carried out with the help of PCB

• Process Scheduling: The different information like Process priority, process state, and resources used can be used by the OS to schedule the process on the execution stack. The scheduler checks the priority and other information to set when the process will be executed.
• Multitasking: Resource allocation, process scheduling, and process synchronization altogether helps the OS to multitask and run different processes simultaneously.
• Context Switching: When context switching happens in the OS the process state is saved in the CPU register and a copy of it is stored in the PCB. When the CPU switches to another process and then switches back to that process the CPU fetches that value from the PCB and restores the previous state of the process.
• Resources Sharing: The PCB stores information like the resources that a process is using, such as files open and memory allocated. This information helps the OS to let a new process use the resources which are being used by any other process to execute sharing of the resources.

Advantages of Using Process Control Block

• As, PCB stores all the information about the process so it lets the operating system execute different tasks like process scheduling, context switching, etc.
• Using PCB helps in scheduling the processes and it ensures that the CPU resources are allocated efficiently.
• When the different resource utilization information about a process are used from the PCB they help in efficient resource utilization and resource sharing.
• The CPU registers and stack pointers information helps the OS to save the process state which helps in Context switching.

Disadvantages of using Process Control Block

• To store the PCB for each and every process there is a significant usage of the memory in there can be a large number of processes available simultaneously in the OS. So using PCB adds extra memory usage.
• Using PCB reduces the scalability of the process in the OS as the whole process of using the PCB adds some complexity to the user so it makes it tougher to scale the system further.

FAQs: Process Control Block in Operating System

1. How is a PCB created and is managed by the OS?

This is an automatic process which is initiated by the OS as soon as a process is started, and all the information is instated inside the PCB. The process scheduler in the OS manages the PCB for each process and updates the different states of the processes.

2. Can a process Manage and modify its PCB on its own?

No, in most cases the processes don’t have any access to its PCB. Almost the total access of the PCBs for all the processes are contained with the operating system and only it hold the permission to Manage and modify the PCB for any process.

3. Can multiple processes share the same PCB?

No, each process that are created even if not active and running have their own PCB and are distinctly made at the time of the creation of each process.

4. How context switching is enabled by OS using PCB?

Context switching is a process/feature that involves the saving of the current state of a process and restore the already saved state of another process to resume it. The role of PCB in this is to save the state/context of a process so that when it is needs to resumed it can be done seamlessly. This helps the operating system to multitask and multi-thread.

5. How does PCB helps in Multitasking?

PCBs helps in Context Switching through which the CPU gets the states of the process running or inactive. This helps the CPU to switch between processes seamlessly and multitask easily.