Abstract: The deleted dataset space release system provides facilities in a dynamically mapped virtual memory data storage subsystem to immediately release the physical space occupied by a deleted dataset for use by the data storage subsystem to store subsequently received data files. This system also provides data security by preventing the unauthorized access to the data of scratched data files, both in cache memory and on the data storage devices. The deleted dataset space release system utilizes a user exit in the host processor data file scratch routine to transmit information to the data storage subsystem indicative of the host processor data file scratch activity. Existing channel command words are used in a manner that is transparent to the host processor. The data storage subsystem thereby immediately receives an indication that the host processor is scratching a data file from the volume table of contents of a virtual volume.

Abstract: The read/write head buffer provides a buffer memory for each read/write head in the rotating media data storage system to that a seek request from the processor can be handled as soon as the beginning of the requested data record is positioned below the associated read/write head. The data image stored on the rotating media is read from the rotating media by the read/write head and stored in the read/write head buffer independent of the availability of a data communication path to the processor. Thus, the read data operation need not be synchronized with the availability of a data communication path to the processor and the requested data is retrieved from the rotating media as soon as the data record is properly positioned. In no case is the data retrieval time greater than one revolution of the rotating media. The error correction codes written on the rotating media to protect the integrity of the requested data are maintained since they are stored in the read/write head buffer along with the data record.