With InterProcess Communication: if a storage is shared among two or more processes, for reading and writing, we need to find a way to prohibit more than one process from reading and writing the shared data at the same time disabling interrupts is a simple and attractive approach for user processes to achieve mutual exclusion strict alternation alternates strictly between processes entering their critical sections, while optimizing CPU performance TSL (Test and Set Lock) instruction provides help from hardware to solve the mutual exclusion problem by locking the system bus