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Process concept

A process includes a program in execution on a computer. Each process is represented by a process control block that contains information like a unique pointer, priority, program counter, registers, context data, I/O status, and accounting information. A process can be in one of several states like new, ready, running, waiting, or terminated.

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Process A Process includes A program in execution An instance of a program running on a computer The entity that can be assigned to and executed on a processor A unit of activity characterized by the execution of a sequence of instructions a current state and an associated set of system resources
Process Control Block Each process in operating System is represented by a process control block. It is also called task control block. It contains many pieces of information associated with a specific process-
Program Counter Pointer Priority Process Status I/O Status Information Context Data Accounting Information ……… . ……… Registers Process Control Block
Pointer Pointer A unique pointer associated with this process to distinguish it from all other processes. Process Status The state may be new, ready, running waiting, halted and so on… Priority Priority level relative to other processes
Program Counter The counter indicates the address of the next address of the next address Registers The registers vary in number and type depending on the computer architecture. It include accumulators, index registers, stack pointers and general purpose registers.
Context Data These are data that are present in registers in the processor while the process is executing I/O Status Information The information includes the list of I/O devices allocated to this process, a list of open files and so on. Accounting Information This information includes the amount of CPU and real time used, time limits, account numbers, job or process numbers and so on.
Process State The State of a process is defined in part by the current activity of that process. As a process executes it changes states. Each process may be in one of the following state
New Ready Waiting Running Terminated Interrupt Scheduler Dispatch exit admitted I/O or event wait I/O or event completion
New The process is being created Running Instructions are being executed Waiting The process is waiting for some event to occur like I/O operation etc. Ready The process is waiting to be assigned to a processor Terminated The process has finished execution
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