Use of a pushdown stack or LIFO implemented in hardware as a data memory. This permits the use of zero-address instructions where both operand sources and result destinations are implicitly the top locations of the stack, thus making programs more compact. Stack mechanisms are also used to provide a way of keeping track of multiple interrupts in which the stack serves as a way of ‘nesting’ the interrupts so that those of lesser priority are pushed down so that those of higher priority can be attended to.