HP DDS/DAT tape drives UNIX, Linux and OpenVMS configuration guide (DW049-90930, May 2010)

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 drives support asynchronous, synchronous and narrow (8-bit) wide
transfers.
DDS Digital Data Storage is a recording format that builds on the DAT format to
support the storage of computer data. It was developed originally by
Hewlett-Packard and Sony as an industry standard. The first generation standard
was DDS-1 (or simply DDS), to which was added data compression to produce
the DDS-DC standard.
Further enhancements, notably narrower tracks and thinner tape, led to DDS-2,
which can typically provide double the capacity of DDS-1.
DDS-3 uses a new magnetic coating on the tape that allows twice the recording
density. Together with the use of time-tracking, this gives a DDS-3 tape
approximately three times the capacity of a DDS-2 tape.
UNIX, Linux and OpenVMS configuration guide 45