·       Process
-        A process is  a program in execution.
-        A process is defined as an entity which represent the basic unit of work to be implemented in the system.
-        The term process was the first used by the operating system designer of the MULTICS system in 1960s.
-        A process can also be defined as instance of program in execution.
-        A process can also be defined as instance of program in execution.
-        A process can also be defined as “Locus of Control” in execution.
-        When a process executes it change its state which is known as “Life Cycle of a process”.
-        A program which is in execution mode is called Instance.

·       Process State
-        When a process executes it changes their sates.
-        The state of any process is defined by the current activity which the process is performing.
*      Different States of any process at given time
a.     NEW :- The process is being used.
b.    READY :- The process is waiting to be assigned to a processor.
c.     RUNNING :- Instructions are being executed.
d.    WAITING / SUSPENDED / BLOCKED :- The process is waiting for some event to occur.
e.    HALTED / TERMINATED :- The process has finished execution.

·       Process Control Block
-        Process Control block is also known as task control block.
-        When any process execute from the admission till termination of the process. It needs some information to be stored for its uniform execution, that’s why operating system’s needs process control block to store such information.
-        Process Control block is the data structure used by the operating system.     

·       Description
a)    Pointer
-        It is used to refer the address of the next process control block for maintaining the importance of the information.
b)    Process State
-        Program Counter used by process control block is responsible for storing the next instruction of any process so that it can be executed efficiently.
c)     CPU resisters
-        CPU resisters are used by the process control block so that instructions can be easily retrieve and process the with the help of general purpose resisters, stock pointers, Index resisters, etc.
d)    Memory Allocation
-        Process control block also keep records of the allocated and deallocated memory allocations.
e)    Event Information
-        Process Control block is also responsible to handle the information related to input output operation. So, that resources can be managed efficiently.

Note :- Process Control Block not only stores the above set functions but it also stores process Id, Process Number, Page Fault, etc.

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