Abstract: A method for providing data storage capacity on demand comprises disabling a set of slot elements and data transfer elements of a data library disallowing access to the disabled set by end users of the library, partitioning at least a portion of a set of active data media storage slot elements and active data transfer elements of the data library, exclusive of the disabled set, into partitions for use by the end users; and redefining the sets in response to changes in storage capacity rights of the end users.

Abstract: A method for providing data storage capacity on demand comprises disabling a set of slot elements and data transfer elements of a data library disallowing access to the disabled set by end users of the library, partitioning at least a portion of a set of active data media storage slot elements and active data transfer elements of the data library, exclusive of the disabled set, into partitions for use by the end users; and redefining the sets in response to changes in storage capacity rights of the end users.

Abstract: A tape packet assembler/disassembler (TPAD) for a tape drive accumulates host-transmitted records, which may or may not be blocked by the host. The accumulated host-transmitted records are combined into packets comprising a data portion made up of data blocks and of a trailer portion made up of table entries describing how to disassemble the packet. Host-transmitted commands to write a tape mark are intercepted by the TPAD and replaced by corresponding information in the trailer. Packets are accumulated in a buffer in the TPAD, and are written to the tape drive when the buffer becomes full, or upon a command from the host to reposition the tape, such as rewind. The interblock gaps that would ordinarily separate the host-transmitted records now separate packets, resulting in a considerable increase in the efficiency of tape utilization. The TPAD maintains in the trailer various pointers to assist in forward and back spacing by file and records.

Abstract: A logic circuit in an integrated circuit implementation of an adaptive data compression algorithm which uses a RAM to store dictionary entries. The logic circuit generates predetermined codewords for single-character strings without accessing the dictionary. The logic circuit also generates single-character strings for corresponding codewords without accessing the dictionary.

Abstract: A tape packet assembler/disassembler (TPAD) for a tape drive accumulates host-transmitted records, which may or may not be blocked by the host. The accumulated host-transmitted records are combined into packets comprising a data portion made up of data blocks and a trailer portion made up of table entries describing how to disassemble the packet. Host-transmitted commands to write a tape mark are intercepted by the TPAD and replaced by corresponding information in the trailer. Packets are accumulated in a buffer in the TPAD, and are written to the tape drive when the buffer becomes full, or upon a command from the host to reposition the tape, such as rewind. The interblock gaps that would ordinarily separate the host-transmitted records now separate packets, resulting in a considerable increase in the efficiency of tape utilization. The TPAD maintains in the trailer various pointers to assist in forward and back spacing by file and records.

Abstract: A data compression system implementing expansion protection employs one or more pairs of FIFOs to compare the lengths of raw and processed versions of a block of received data. The shorter version is transmitted so that the data transmitted by the data compression system is at most negligibly expanded relative to the system input. A code is inserted in the output stream to indicate the beginning of the transmission of a raw data block so that a receiving or retrieving system can determine whether the data following needs to be decompressed or not. Further codes can be injected to indicate a switch from raw data to processed data in the output of the compression system.

Abstract: An adaptive data compression system is reset when performance drops below a predetermined threshold to permit greater compression of long files with evolving distributions of symbol combinations. The compression system uses a resettable dictionary in which initially unassigned codes are strategically assigned to symbol combinations as they are encountered in the data stream.The difference between the bit-lengths of corresponding lengths of the compressor input and output is compared with a value representing a predetermined performance threshold. The dictionary can be reset if the actual performance falls below the performance threshold. The reset can be inhibited while the dictionary is less than half-full to ensure that performance measures are statistically significant. However, if the performance is such that data expansion is occurring, reset is not so delayed.