A process is the unit of work in a modern computing system. A system consists of a collection of processes, some executing user code, others executing operating system code.
The status of the current activity of a process is represented by the value of the program counter and the contents of the processor’s registers. The process memory is typically divided into Text Section, Data Section, Heap Section and Stack Section. The Text section carries the executable code, the Data section holds global variables, the Heap section is dynamically allocated during program run time and the Stack section keeps temporary data storage for function return, local variables etc.
The size of the text and data sections are fixed whereas the stack and heap sections can shrink and grow dynamically during program execution.
A program is a passive entity containing a list of instructions stored on disk whereas a process is an active entity with a program counter specifying the next instruction to execute and a set of associated resources. A program becomes a process when an executable file is loaded into memory.
Process States
New - Process created
Running - Under execution
Waiting - Waiting for some event to occur
Ready - Waiting to be assigned to a processor
Terminated - Finished execution
Each process is represented in the operating system by a process control block (PCB). The PCB contains the information associated with a specific process such as Process state, program counter, CPU Register, CPU scheduling info, memory management info, Account info and I/O information.