IBM T400F manual Glossary, Numbers and Symbols

Glossary

This glossary defines the special terms, abbreviations, and acronyms that are used in this publication.

Numbers and Symbols

2:1 compression. The relationship between the quantity of data that can be stored with compression as compared to the quantity of data that can be stored without compression. In 2:1 compression, twice as much data can be stored with compression as can be stored without compression.

µs. Abbreviation for microsecond or one millionth of a second (.000001 s).

A

A.See ampere.

acclimation time. Pertaining to the Ultrium 2 Tape Drive, the amount of time that is needed for the drive to adjust to change in temperature, altitude, climate, or environment.

active. The condition that the SCSI bus is in when a server is trying to use one or more devices on the bus.

adapter. See adapter card.

adapter card. A circuit board that adds function to a computer.

AL_PA. See Arbitrated Loop Physical Address.

amp. See ampere.

ampere (A, amp). A unit of measure for electric current that is equivalent to a flow of one coulomb per second, or equivalent to the current produced by one volt applied across a resistance of one ohm.

American National Standards Institute. A private, non-profit organization that gathers and disseminates information about standards and conformity issues that affect the business, government, and people of the United States.

ANSI. See American National Standards Institute.

Arbitrated Loop Physical Address (AL_PA). An 8-bit value that identifies a device in an arbitrated loop. All Fibre Channel ports communicate by using AL_PAs.

autosense data. Sent by the drive to the server, sense data that automatically accompanies a Check Condition in response to an error. The server does not need to send a REQUEST SENSE command to get the

sense data. Autosense data is available only in the Fibre Channel version of the Ultrium 2 Tape Drive (Model T400F).

B

backhitch. During tape movement (reading or writing), the condition that occurs when the tape drive must stop the tape, reverse it, and restart tape motion due to certain events. A backhitch usually occurs when the server’s net (compressed) data rate is less than the drive’s data rate.

backreflection. Pertaining to instances where light is launched into an optical fiber in a forward direction, the light that is returned to the launch point in the reverse direction.

backups. The short-term retention of records used for restoring essential business and server files when vital data has been lost because of program or server errors or malfunctions.

backward compatible. Capable of being used with a previous product that was designed for a similar purpose. For example, a tape cartridge that is designed to be used with a modern tape drive but can also be used with certain older tape drives. Synonymous with downward compatible.

bar code. A code that represents characters by sets of parallel bars of varying thickness and separation. The bars are read optically by transverse scanning.

bar code label. A slip of paper bearing a bar code and having an adhesive backing. The bar code label must be affixed to a tape cartridge to enable the library to identify the cartridge and its volume serial number.

bezel. The removable frame that fits over the front of the Ultrium 2 Tape Drive.

bit. The smallest unit of data in a computer. A bit (short for binary digit) has a single binary value (either 0 or 1). Computers store data and execute instructions in bit multiples called bytes. In most computer systems, there are eight bits in a byte.

burst data transfer rate. The maximum speed at which data is transferred.

bus. See SCSI bus.

byte. A string that consists of a certain number of bits (usually 8) which are treated as a unit and represent a character. A byte is a fundamental unit of data.

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