glossary 165
Glossary
algorithm A rigorous set of rules for a procedure. In the context of data compression, the
rules are for transforming the way data is represented.
ANSI American National Standards Institute, which sets standards for, amongst
other things, SCSI and the safety of electrical devices.
asynchronous see
data transfer phase
BOM Beginning Of Media. The first point on the tape that can be accessed by the
drive.
checksum The sum of a series of bytes written to the tape, which can be checked against
the sum of the same series of bytes when the tape is read in order to identify
errors.
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.
compression ratio A measure of how much compression has occurred, defined as the ratio of the
amount of uncompressed data to the amount of compressed data into which it
is transformed. The LTO-DC algorithm can typically achieve a compression
ratio of between 2:1 and 4:1 depending on the nature of the data.
data set A fixed-size block of compressed host information. (404,352 bytes)
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
glossary
