ATTO Technology operation manual SCSI is a key technology for storage, Glossary

2 SCSI is a key technology for storage

SCSI is a serial communications technology designed to transfer large amounts of data between a variety of hardware systems over long distances. It is a key technology for applications that require shared, high bandwidth access to storage.

SCSI provides a logical point-to point serial channel for the transfer of data between a buffer at a source device and a buffer at a destination device. It moves buffer contents from one port to another, without regard to the format or meaning of the data so different upper level protocols are able to run over SCSI hardware.

The SCSI architecture is structured as a hierarchical set of protocol layers. Defined within these layers are rules for signal interfaces, serial encoding and decoding, error control, frame format and communications protocols.

Glossary

Some terms used in the SCSI industry are defined below. More information is available through the ATTO Technology website (www.attotech.com), and the SCSI Consortium (www.iol.unh.edu/consortium).

Term	Definition
ANSI	American National Standards Institute
auto negotiation	hardware senses and automatically responds depending on configuration
BER	Bit Error Rate: a measure of transmission accuracy; the ratio of bits received in
	error to bits sent
bit	Smallest unit of data a computer can process: a single binary digit with a value
	of either 0 or 1
byte	an ordered set of 8 bits
CRC	Cyclic Redundancy Check: an error-correcting code which calculates a numeric
	value for received and transmitted data. If no error has occurred during
	transmission, the CRC for both received and transmitted data should be the
	same.
host	a processor, usually a CPU and memory, which communicates with devices
	over an interface
initiator device	A component which originates a command
LED	Light-emitting diode: a type of diode that emits light when current passes
	through it. Visible LEDs are used as indicator lights on all sorts of electronic
	devices.
originator	an initiating device; a component which originates a command
receiver	the ultimate destination of data transmission; a terminal device

3 ATTO Technology ExpressPCI Ultra/WIDE SCSI Host Adapters Installation and Operation Manual