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