MVS OPEN, CLOSE and EOV processing

 The OPEN macro verify the volume and dataset password. For tape, it writes volume label. It then passes vi trip to access method. 

The Close macro update the dscb in vtoc. For tape processing it writes the tape mark and reposition the tape. 

EOV handle the situation when the write reach the end of volume transparently to the application. It extends the dataset to another disk or tape volume.  For disk, VTOC is updated. For tape, you t will ask to mount another volume and continue writing.