2 SCSI is a key technology for storage. ATTO Technology ATTO ExpressPCI Ultra/WIDE SCSI Host Adapters Express PCI PSC: Single-Channel Single-Ended Ultra/WIDE ExpressPCI DC: Dual-Channe, ATTO ExpressPCI Ultra/WIDE SCS, ATTO ExpressPCI Ultra/WIDE SCSI Host Adapters Express PCI PSC: Single-Channel Single-Ended Ultra/WIDE ExpressPCI DC: Dual-Channel Single-Ended Ultra/WIDE

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

ANSI auto negotiation

BER bit byte

CRC host initiator device

LED originator receiver

Definition

American National Standards Institute hardware senses and automatically responds depending on configuration

Bit Error Rate: a measure of transmission accuracy; the ratio of bits received in error to bits sent

Smallest unit of data a computer can process: a single binary digit with a value of either 0 or 1 an ordered set of 8 bits

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.

a processor, usually a CPU and memory, which communicates with devices over an interface

A component which originates a command

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.

an initiating device; a component which originates a command the ultimate destination of data transmission; a terminal device

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

Term

SCSI topology transceiver transfer rate

Definition

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. logical layout of the parts of a computer system or network and their interconnections a transmitter/receiver module the rate at which bytes or bits are transferred, as in megabytes or gigabits per second.

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