HP DDS/DAT drives UNIX, Linux and OpenVMS configuration guide (DW049-90915, November 2009)

HP Evolution II DDS/DAT drives: UNIX, Linux and OpenVMS configuration guide 39
Glossary
AT&T mode 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 mode 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.
block A logical unit of information. Called “record” in the DDS-format specification.
BOP Beginning Of Partition. The position at the beginning of the permissible recording
region of a partition.
buffered mode A mode of data transfer in write operations that facilitates tape streaming.
compression 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 done by
representing strings of bytes with codewords.
DAT Digital Audio Tape
data transfer
phase
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.
In synchronous data transfer, the initiator and target work in synchronization, allowing
transmission of a packet of data to start before acknowledgment of the previous
transmission.
In wide (16-bit) data transfer, two bytes are transferred at the same time instead of a
single byte.
HP DDS/DAT drives support asynchronous, synchronous and narrow (8-bit) wide
transfers.