(1) Field of the Invention
The present invention relates to task switching in computer operating systems, and in particular, to a task switching apparatus for switching the task to be completed in a processor by switching to the time slot to which a task is assigned.
(2) Description of the Related Art
Main operations of computer operating systems are hardware management, task management, data management and input/output management. Task management in those operations is for managing task execution sequence and an important function for having a CPU, a memory, an input/output device and the like operate efficiently.
Task is a control unit for performing a centralized control on the program operation flow such as its startup, execution and end. Programs that operate under the management of the computer operating systems are used as tasks, and operations in the computer operating system relating to the program are completed on the basis of task.
There are algorithms for determining task execution sequence called time sharing scheduler system or priority switching method. The time sharing scheduler system is a method where a certain execution time is assigned to a task, an execution right of a processor is given to the processor during the assignment time, and the execution right of a processor is given to another processor after the assignment time. This method makes it possible to assign the execution right in certain execution time to all the tasks equally.
Also, as to the priority switching method, patent library 1 and 2 disclose a scheduling apparatus for switching tasks according to task priorities.    (Patent Library 1) Japanese Laid-Open Patent application No. 2000-20323.    (Patent Library 2) Japanese Laid-Open Patent application No. 1992-101233.
However, the above-mentioned prior art includes a problem that designing programs is difficult in that a programmer specifies the priority of each task in order to secure the necessary performance of each task, and that alteration of the programs cannot be flexibly made once they are designed.