PURPOSE: To make it possible to instruct for a standby point in instruction sequence by placing a stopped task on the queue of an operating system so as to be processed afterward, then assigning a central processing unit to the next task on the queue.

CONSTITUTION: When a HALT instruction is executed in a protective mode environment, the task reflects generates a general memory protection exception type O (140). A general protection handler always staying in the operating system makes inspection in order to judge whether the source for the occurrence of this exception is the HALT or not (142). If this exception is by the HALT, the register state of the task where the exception occurs is stored in the memory so as to be restored for the purpose of later processing (146). This task is placed on the ready queue so as to be scheduled afterward (148). Next, the operating system assigns the CPU to the next task on the ready queue.