ISA S61.2 : 1978

Presents external procedure references for use in industrial computer control systems. These external procedure references provide means for accessing files, and also provide means for resolving problems of file access contention in a multiprogramming/multiprocessing environment. In such an environment, it is expected that concurrent programs will attempt to access the same file at the same time; therefore, the external procedure references defined in this standard provide the information necessary for the processor to resolve such simultaneous access in an orderly manner. The method for resolution of access control is left to the processor.