HP Ultrium Tape Drive manual Glossary

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.
BOT	Beginning Of Tape. The first point on the tape that can be accessed by the drive.
buffered mode	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.
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
	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.
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 Ultrium drives support asynchronous, synchronous and narrow (8-bit) wide
	transfers.

Glossary

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