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January 10, 2014

Process Concept of Operating Systems


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Friends, in our last post we have discussed about the introduction and basis of Operating Systems. Today we shall discuss about the Process concept of Operating Systems. In simple words we can say that the process is a Program under execution. The process is an executing program that includes the current values of the program counter, registers and variables. Each process has its own virtual CPU. If a program is being executed by CPU, then we can say that the program is under CPU burst, if CPU burst is going on, then the program is called "Process"

Process States :

As a process executes, it changes states. the state of a process is defined by the current activity of that process. In order to manage switching between processes, the operating system defined various states. The various states of the processes are as follows.
  1. New : Process is being created
  2. Running : CPU is allocated for the process
  3. Blocked : Waiting for an event to happen
  4. Ready : Waiting for processor to be assigned
  5. Terminated : Finished execution
Now lets have a detailed look on the above mentioned states of process.

New : If the process is in the new state, it means that the process is being created. Only memory is allocated but not CPU.

Running : The process is said to be running (i.e., in running state) if it has the CPU and the instructions are being executed. CPU is allocated and there is only one process which is executed by the CPU. In multiprocessor system and with multiple CPUs, there will be many running processes and the operating system will have to keep track of all of them.

Blocked : A process is said to be blocked (i.e., in blocked state) if it is waiting for an event to happen such as an I/O completion event before it can proceed. Until the event is completed the process cannot proceed further. A process can also be blocked due to reception of signal.

Ready : A process is said to be ready (i.e., in ready state) if it is waiting to be assigned to a processor so that it could use a CPU if one was available. In ready state the process is neither waiting for any external event such as an I/O operating nor it is running. In ready state the program is waiting for CPU in ready queue.

Ready Queue : The major difference between a blocked and a ready process is that a blocked process cannot be directly scheduled even if the CPU is free, whereas, a ready process can be scheduled if the CPU is free.

Terminated : If a process enters the terminated state, it means that the process has finished execution of its tasks. After the process has finished execution, it's result is displayed.

Rajesh Prasad . M
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