HP C1537A Technical Reference Manual page 54

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.
DDS-4 uses longer tapes (150m). HP's DDS-4 drives, which are ultra-wide
SCSI devices, allow transfer rates from 3 to 4 times greater than DDS-3 and
capacities that are two-thirds as much again.
DAT 72 uses longer tape again (170m) with narrower tracks to achieve a
greater data density leading to capacity of 72 MB (with 2:1 data
compression).
filemark A mark written by the host to the tape that can be searched for, often using
the drive's fast-search capability. It does not necessarily separate files. It is up
to the host to assign a meaning to the mark.
group A fixed capacity set of tracks written to or read from tape, defined in the DDS
format.
immediate mode A mode of responding to SCSI commands where the drive or other peripheral
does not wait until the command has finished before returning status
information back to the host. For writing filemarks, Immediate mode can
significantly improve the performance of systems that do not set the
Immediate bit when sending a SCSI command. On the other
WRITE FILEMARKS
hand, data is not flushed to tape in response to a filemark command.
By default, the buffer in the drive is flushed every 5 seconds. Infinite flush
infinite flush
avoids frequent starting and stopping of the mechanism when using a very
slow application. It also avoids losing capacity through the flushing of partly
written groups. On the other hand, infinite flush means that data can remain
54 glossary