What is Process, Multiprogramming, Context switching ?

Lists of Questions answers And Study notes on “OS Process and Threads”

  • (1) What is Process? Give the difference between Process and Program.
  • (2) What is multiprogramming?
  • (3) What is context switching?

 

Question-1 what is Process? Give the difference between Process and Program.

Process:

  • Process is a program under execution.
  • It is an instance of an executing program, including the current values of the program counter, registers & variables.
  • Process is an abstraction of a running program.
Process Program
A process is program in execution. A program is set of instructions.
A process is an active/ dynamic entity. A program is a passive/ static entity.
A process has a limited life span. It is created when execution starts and

terminated as execution is finished.

A program has a longer life span. It is stored on disk forever.
A process contains various resources like memory address, disk, printer

etc… as per requirements.

A program is stored on disk in some file.It does not contain any other resource.
A process contains memory address which is called address space. A program requires memory space on disk to store all instructions.

 

 

Question-2 what is multiprogramming?

A process is just an executing program, including the current values of the program counter, registers, and variables.

  • Conceptually, each process has its own virtual CPU.
  • In reality, the real CPU switches back and forth from process to process, but to understand the system, it is much easier to think about a collection of processes running in
  • (pseudo) parallel, than to try to keep track of how the CPU switches from program to program.
  • This rapid switching back and forth is called multiprogramming and the number of processes loaded simultaneously in memory is called degree of multiprogramming.

 

Question-3 what is context switching?

  • Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process.
  • This task is known as a context switch.
  • The context of a process is represented in the PCB of a process; it includes the value of the CPU registers, the process state and memory-management information.
  • When a context switch occurs, the kernel saves the context of the old process in its PCB and loads the saved context of the new process scheduled to run.
  • Context-switch time is pure overhead, because the system does no useful work while switching.
  • Its speed varies from machine to machine, depending on the memory speed, the number of registers that must be copied, and the existence of special instructions.

context switching