- [Instructor] A program is an executable file
that is stored on disk.
A program is a passive entity until it is launched,
at which time it becomes a process.
This makes a process a running instance of a program.
When a process is created by running a program,
it's allocated some system resources
including memory and a process ID number, or PID.
Every process has a unique ID number.
Each process has a parent process that started it.
This parent process also has a process ID number.
A process can spawn other processes called child processes.
The process ID number is used by the kernel
to manage and control the process during its lifetime.
System administrators use the process ID
for changing task priority and ending tasks.
Processes are organized in a hierarchical manner,
just like files and folders.
So the child processes are nested
under the parent processes, and so on.
When a process ends,
it is reported back to the parent process.
Its resources are freed,
and the process ID is removed.