fork() causes the current process to reun itself again and these lines of execution run concurrently from the point at which fork() is called.
A process is a program in execution. The main process has a line of execution. For each call to fork() that line of execution splits. The main process continues but there is now a child process which continues from the same point. If fork() is called once, then a new branch of exection spins off and each branch exectes the same code from the same point forward, even another call to fork()
For every subsequent fork() each current line of execution must branch. For 1 call it's 2 branches, for 2 it's 4, for 3 it's 8 and so on. total_pids = 2^number_of_forks.
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