PROGRAM OPERATING SYSTEM

PURPOSE:To prevent a control table from being destroyed by mis-programming by copying a fundamental control table on a system working area when a request to open a file is issued. CONSTITUTION:When the request to open the file is issued from the high-order program 10 of a transaction system, the control table 4 that exists in the high- order program 10 is copied on the system working area 11 accessible from only a low-order program 3. A bidirectional pointer is stretched between the control table 4 of a processing requestor and a copied control table 11a by using a timing to open the file, and also, a fundamental parameter that is a parameter unchangeable until the processing is completed is left in the control table 11a. Thereby, it is possible to prevent the fundamental parameter destroyed due to erroneous access from the high-order program 10, which prevents the control table destroyed due to the mis-programming.