multiprocessing

multiprocessing is the act of switching between multiple processes so fast that it appears multiple processes are running concurrently.
OS schedules tasks each program gets a little time, then has to wait in a turn to continue executing base level syscalls that requires waiting will be moved off before finishing, and in the meantime others can wait. like file read.
program A program is a script to be ran.
process a process is an instance of a program. Every process has a unique identifier, each process is uniquely identified by a PID.
syscall get_pid will give you back the PID.
open file table open file table is a system wide for each file opening session, mentioning what the mode and cursor of the file is open, and the number of file descriptor tables pointing to it with a refcount.
When we call close, the refcount decrements. When refcount=0, the file is deleted. This means, if you share a pipe, both parent and child has to close the pipe.
read blocks until at least 1 byte is available, or until all write ends are closed.