Process Management of Operating Systems.

This contains os process management

1. 1.Introduction 2.Process States 3.Process Control Block Process Management

2. A process is a program in execution. For example, when we write a program in C or C++ and compile it, it becomes a process. Process Management PROCESS V/S PROGRAM A Program is a Piece of code which may be single line or multiple lines .A computer program is a collection of instructions that perform a specific task.

3. Process States The current activity of a process is known as its state. The five state process model is defined as following.

4. 1.New When a program which is going to be picked up by the OS into the main memory is called a new process. OR The process is in new state when it has just been created 2. Ready The processes which are ready for the execution and reside in the main memory are called ready state processes. There can be many processes present in the ready state. 3.Running When t he process instructions are being executed by the processor. if we have only one CPU in our system, the number of running processes for a particular time will always be one. If we have n processors in the system then we can have n processes running simultaneously.

5. 4. Block/ wait When a process waits for a certain resource to be assigned or for the input from the user then the OS move this process to the block or wait state and assigns the CPU to the other processes. block or wait state depending upon the scheduling algorithm. 5 . Terminated When a process finishes its execution, it comes in the termination state. All the context of the process (Process Control Block) will also be deleted the process will be terminated by the Operating system.

6. Process Control Block Process Number(ID) Process States Pointer Program Counter Priority General Purpose Registers Open Files List Accounting and status Data A process control block is associated with each of the processes. It contains important details about that particular process. These are as follows: Process Attributes

7. Attributes of a PCB 1.Process ID:- When a process is created, a unique id is assigned to the process which is used for unique identification of the process in the system. 2. Process State The Process, from its creation to the completion, goes through various states which are new, ready, running and waiting. 3.Pointer This is stack pointer store current position of the process.

8. Process Control Block 4. Program counter A program counter stores the address of the last instruction of the process on which the process was suspended. The CPU uses this address when the execution of this process is resumed. 5. Priority Every process has its own priority. The process with the highest priority among the processes gets the CPU first. This is also stored on the process control block. 6. General Purpose Registers Every process has its own set of registers which are used to hold the data which is generated during the execution of the process.

9. Attributes of a PCB continue 7. List of open files During the Execution, Every process uses some files which need to be present in the main memory. OS also maintains a list of open files in the PCB. 8. Accounting and Status of data This field include information about the amount of CPU used, process numbers.

10. Process scheduling Process scheduling is the activity of the process manager that handles the removal of the running process from the CPU and the selection of another process based on a particular strategy.

11. Schedulers Schedulers are special system software which handle process scheduling in various ways. Their main task is to select the jobs to be submitted into the system and to decide which process to run. Types of Schedulers − Long-Term Scheduler Short-Term Scheduler Medium-Term Scheduler

12. 1. Long Term or Job Scheduler It is also called a job scheduler. It brings the new process to the ‘Ready State’. 2. Short-Term or CPU Scheduler It is also called as CPU scheduler. Its main objective is to increase system performance in accordance with the chosen set of criteria. It is the change of ready state to running state of the process. Short-term schedulers, also known as dispatchers, make the decision of which process to execute next. Short-term schedulers are faster than long-term schedulers. Types of Scheduler

13. Scheduler

14. Types of Scheduler 3. Medium-Term Scheduler It is responsible for suspending and resuming the process. Medium-term scheduling is a part of swapping. In this condition, to remove the process from memory and make space for other processes, the suspended process is moved to the secondary storage. This process is called swapping.  It reduces the degree of  multiprogramming .

15. Comparison among Scheduler Long-Term Scheduler Short-Term Scheduler Medium-Term Scheduler It is a job scheduler It is a CPU scheduler It is a process-swapping scheduler. Speed is lesser than short term scheduler Speed is the fastest among all of them. Speed lies in between both short and long-term schedulers. It controls the degree of multiprogramming It gives less control over how much multiprogramming is done. It reduces the degree of multiprogramming It can re-enter the process into memory, allowing for the continuation of execution. It selects those processes which are ready to execute It can re-introduce the process into memory and execution can be continued.

16. Criteria of CPU Scheduling CPU utilization Turnaround Time Waiting Time Response Time Completion Time

17. 1.CPU utilization The main objective of any CPU scheduling algorithm is to keep the CPU as busy as possible. A high CPU utilization indicates that the CPU is busy and working efficiently, processing as many tasks as possible. 2. Throughput A measure of the work done by the CPU is the number of processes being executed and completed per unit of time . This is called throughput. A high throughput indicates that the system is processing tasks efficiently, which can lead to increased productivity and faster completion of tasks.

18. 3. Turnaround Time The time elapsed from the time of submission of a process to the time of completion is known as the turnaround time. Turn Around Time = Completion Time - Arrival Time. 4. Waiting Time  it measures the amount of time a task or process waits in the ready queue before it is processed by the CPU. Waiting Time = Turnaround Time - Burst Time.

19. Response Time Response Time = CPU Allocation Time(when the CPU was allocated for the first) - Arrival Time Completion Time The completion time is the time when the process stops executing,  which means that the process has completed its burst time and is completely executed. Arrival Time:  Time at which the process arrives in the ready queue. Completion Time:  Time at which process completes its execution. Burst Time:  Time required by a process for CPU execution. Turn Around Time:  Time Difference between completion time and arrival time.