Tag: Process States in Operating System

Process Control Block | Process Attributes

Operating System

Process Control Block-

 

  • Process Control Block (PCB) is a data structure that stores information about a particular process.
  • This information is required by the CPU while executing the process.

 

The Process Control Block of a process looks like-

 

 

  • Each process is identified by its own process control block (PCB).
  • It is also called as context of the process.

 

Process Attributes-

 

The various attributes of process stored in the PCB are-

 

1. Process Id-

 

  • Process Id is a unique Id that identifies each process of the system uniquely.
  • A process Id is assigned to each process during its creation.

 

2. Program Counter-

 

  • Program counter specifies the address of the instruction to be executed next.
  • Before execution, program counter is initialized with the address of the first instruction of the program.
  • After executing an instruction, value of program counter is automatically incremented to point to the next instruction.
  • This process repeats till the end of the program.

 

3. Process State-

 

  • Each process goes through different states during its lifetime.
  • Process state specifies the current state of the process.

 

Read more- Process States in OS

 

4. Priority-

 

  • Priority specifies how urgent is to execute the process.
  • Process with the highest priority is allocated the CPU first among all the processes.

 

5. General Purpose Registers-

 

  • General purpose registers are used to hold the data of process generated during its execution.
  • Each process has its own set of registers which are maintained by its PCB.

 

6. List of Open Files-

 

  • Each process requires some files which must be present in the main memory during its execution.
  • PCB maintains a list of files used by the process during its execution.

 

7. List of Open Devices-

 

  • PCB maintains a list of open devices used by the process during its execution.

 

Important Notes-

 

  • PCB of each process resides in the main memory.
  • There exists only one PCB corresponding to each process.
  • PCB of all the processes are present in a linked list.

 

To gain better understanding about Process Control Block,

Watch this Video Lecture

 

Next Article- Schedulers in OS

 

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Process States in Operating System

Operating System

Process States in Operating System-

 

Each process goes through different states in its life cycle-

 

 

1. New State-

 

  • A process is said to be in new state when a program present in the secondary memory is initiated for execution.

 

2. Ready State-

 

  • A process moves from new state to ready state after it is loaded into the main memory and is ready for execution.
  • In ready state, the process waits for its execution by the processor.
  • In multiprogramming environment, many processes may be present in the ready state.

 

3. Run State-

 

  • A process moves from ready state to run state after it is assigned the CPU for execution.

 

4. Terminate State-

 

  • A process moves from run state to terminate state after its execution is completed.
  • After entering the terminate state, context (PCB) of the process is deleted by the operating system.

 

5. Block Or Wait State-

 

  • A process moves from run state to block or wait state if it requires an I/O operation or some blocked resource during its execution.
  • After the I/O operation gets completed or resource becomes available, the process moves to the ready state.

 

6. Suspend Ready State-

 

  • A process moves from ready state to suspend ready state if a process with higher priority has to be executed but the main memory is full.
  • Moving a process with lower priority from ready state to suspend ready state creates a room for higher priority process in the ready state.
  • The process remains in the suspend ready state until the main memory becomes available.
  • When main memory becomes available, the process is brought back to the ready state.

 

6. Suspend Wait State-

 

  • A process moves from wait state to suspend wait state if a process with higher priority has to be executed but the main memory is full.
  • Moving a process with lower priority from wait state to suspend wait state creates a room for higher priority process in the ready state.
  • After the resource becomes available, the process is moved to the suspend ready state.
  • After main memory becomes available, the process is moved to the ready state.

 

Important Notes-

 

Note-01:

 

A process necessarily goes through minimum 4 states.

 

  • The minimum number of states through which a process compulsorily goes through is 4.
  • These states are new state, ready state, run state and terminate state.
  • However, if a process also requires the I/O operation, then minimum number of states is 5.

 

Note-02:

 

A single processor can execute only one process at a time.

 

  • A single processor can not more than one processes simultaneously.
  • If n processors are present in the system, then only n processes can be executed simultaneously.

 

Note-03:

 

State Present in Memory
New state Secondary Memory
Ready state Main Memory
Run state Main Memory
Wait state Main Memory
Suspend wait state Secondary Memory
Suspend ready state Secondary Memory
Terminate state –

 

Note-04:

 

Moving a process from wait state to suspend wait state is a better alternative.

 

  • Consider a process with higher priority arrives and the main memory is full.
  • Then, there are two ways to make room for it.

 

These two ways are-

  1. Moving a process with lower priority from ready state to suspend ready state.
  2. Moving a process with lower priority from wait state to suspend wait state.

 

Out of these-

  • Moving a process from wait state to suspend wait state is a better alternative.
  • This is because the process is already waiting for some blocked resource.

 

To gain better understanding about Process States in Operating System,

Watch this Video Lecture

 

Next Article- Process Control Block | PCB

 

Get more notes and other study material of Operating System.

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