A process is an executing program. The CPU executes a large number of programs. While its main concern is the execution of user programs, the CPU is also needed for other system activities. These activities are called processes. A time-shared user program is a process. Process management is one of the functions of the operating system.
Process vs Program:
| Process | Program |
|---|---|
| 1) A process is an activity. | 1) A program is a group of instructions. |
| 2) A process is a dynamic entity. | 2) A program is a static entity. |
| 3) A process has a high resource requirement; it needs resources like CPU, memory, address, and I/O during its lifetime. | 3) A program does not have any resource requirements; it only requires memory space for storing the instructions. |
| 4) A process has its own control block called the Process Control Block (PCB). | 4) A program does not have any control block. |
| 5) A process exists for a limited span of time, as it gets terminated after the completion of the task. | 5) A program exists at a single place and continues to exist until it is deleted. |
Multiprogramming:
In any multiprogramming system, the CPU switches from process to process quickly, running each for tens or hundreds of milliseconds. This rapid switching back and forth of the CPU is called multiprogramming. In multiprogramming systems, processes are performed in a pseudo-parallelism, as if each process has its own processor. In fact, there is only one processor, but it switches back and forth from process to process.
Keeping track of multiple parallel activities is hard for people to do. Therefore, operating system designers over the years have evolved a sequential process that makes parallelism easier to deal with.
Process Model:
In this model, all the runnable software on the computer, sometimes including the OS, is organized into a number of sequential processes. A process is just an instance of executing a program, including the current values of the program counter, registers, and variables.
