Abstract: A caching method for selecting variable size data blocks for replacement or removal from a cache includes determining the size and the unreferenced time interval of each block in the cache. The size of a block is the amount of cache space taken up by the block. The unreferenced time interval of a block is the time that has elapsed since the block was last accessed, and may be determined using a least recently used (LRU) algorithm. The recall probability of each block in the cache is then determined. The recall probability of a block is a function of its unreferenced time interval and possibly size and other auxiliary parameters. The caching method then determines a quality factor (q) for each block. The (q) of a block is a function of its recall probability and size. The caching method concludes with removing from the cache the block with the lowest (q).

Abstract: The removable media management system operates with a manual, an automated, or a combination of subsets of manual and automated library system to store and retrieve media cartridges for an associated plurality of drive elements. This system enables the use of a plurality of types of media within the single monolithic cartridge library system and a corresponding plurality of drive elements associated with said library system. Thus, each drive element has associated therewith a number of object storage locations within the library system which contains media of a form and content that matches the drive element. The removable media management system maps the correspondence between object storage location, media type, designated drive element in a manner such that the single library is partitioned into subsets for the user, i.e.

Abstract: Control software and hardware in the tape drive control unit creates and manages a header segment at the beginning of the magnetic tape. This header segment includes an administrative information section that contains data relating to the magnetic tape itself. The administrative information includes read/write status information such as the write protect status of the magnetic tape that enables the tape drive control unit to manage the data records written onto the magnetic tape without reference to any other source of administrative data. In addition, each data record written on the magnetic tape includes a header which denotes the read/write status of the data record.

Abstract: This data security arrangement provides a significant level of data security in an automatic magnetic tape cartridge library by isolating the actual data from the control of the data retrieval process. This isolation is accomplished by the use of a plurality of architectural devices that dissociate control and data. The data written on the magnetic tape cartridges cannot be accessed by the library modules. The library modules are not electrically connected to the tape drives or the data bus that connects the tape drives to the host computer. In addition, library software on the host computer emulates an operator's console and intercepts all tape mount commands generated by the host computer. The library software translates these commands into control signals to activate the library module to retrieve a designated magnetic tape cartridge and load this cartridge into a tape drive. Thus, the data retrieval apparatus is separate from the library control apparatus.