Abstract: A method and means are provided to facilitate the exchange of data between a direct access storage device (DASD) and a central processing unit (CPU). The data is stored in fixed length records on the DASD.A pair of sequential commands are issued by the CPU to control access to the DASD data. The first command contains information which defines the boundaries of the DASD storage space which the CPU can access. The second command identifies the operation to be carried out within the permitted space defined in the first command and establishes where within the permitted space the activity is to take place.The use of these two commands reduces the amount of CPU software involvement which is required for data accessing, particularly where the accessing involves the crossing of geometrical boundaries on the DASD.