Specifications

3 ATTO Technology ExpressPCI Ultra3 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.
ATTO Express PCI SCSI host adapters carry SCSI protocol over SCSI.
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
SCSI Small Computer Systems Interface: a processor-independent standard for
system-level interface between a computer and intelligent devices including hard
disks, floppy disks, CD-ROM, printers, scanners, etc.