HP C7401A HP Ultrium Drives Technical Reference Manual V5.0 UNIX Configuration - Page 35

Glossary glossary AT&T mode Berkeley mode BOT buffered mode compression data transfer phase Berkeley and AT&T functional modes differ in "read-only" close functionality. In AT&T mode, a device close operation will cause the tape to be repositioned just after next filemark on the tape (the start of the next file). Berkeley and AT&T functional modes differ in "read-only" close functionality. In Berkeley mode the tape position will remain unchanged by a device close operation. Beginning Of Tape. The first point on the tape that can be accessed by the drive. A mode of data transfer in write operations that facilitates tape streaming. It is selected by setting the Buffered Mode Field to 1 in the SCSI MODE SELECT Parameter List header. A procedure in which data is transformed by the removal of redundant information in order to reduce the number of bits required to represent the data. This is basically done by representing strings of bytes with codewords. In Ultrium drives, the data is compressed using the LTO-DC compression format which is based on ALDC (licensed from Stac/IBM) with two enhancements. One limits the increase in size of data that cannot be compressed that ALDC produces. The other is the use of embedded codewords. On a SCSI bus, devices put in requests to be able to transfer information. Once a device is granted its request, it and the target to which it wants to send information can transfer the data using one of three protocols (assuming both devices support them): asynchronous, synchronous, and wide. In asynchronous transfers, the target controls the flow of data. The initiator can only send data when the target has acknowledged receipt of the previous packet. All SCSI devices must support asynchronous transfer. Glossary 35