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Quantum DLT 4000 Tape Drive 3-1

Chapter 3

SCSI DESCRIPTION

This chapter provides a detailed description of the logical interfaces of the tape drive. The drive is

fully compliant with the ANSI SCSI-2 standard for tape drive devices and implements many optional

features.

3.1 SCSI OVERVIEW

The Small Computer System Interface (SCSI) is a specification for a peripheral

bus and command set that is an ANSI standard. The standard defines an I/O

bus that supports up to eight devices (narrow SCSI).

ANSI defines three primary objectives of SCSI-2:

1. To provide host computers with device-independence within a class of

devices

2. To be backward-compatible with SCSI-1 devices that support bus parity

and that meet conformance level 2 of SCSI-1

3. To move device-dependent intelligence to the SCSI-2 devices

Important features of SCSI-2 implementation include the following:

• Efficient peer-to-peer I/O bus with up to 16 devices

• Asynchronous transfer rates that depend only on device implementation

and cable length

• Logical addressing for all data blocks (rather than physical addressing)

• Multiple initiators and multiple targets

• Distributed arbitration (bus contention logic)

• Command set enhancement

3.2 SCSI COMMANDS

ANSI classifies SCSI commands as mandatory, optional, or vendor-specific. The

mandatory and optional commands implemented for the drives are summarized

in Table 3–1 and described fully in Chapter 5, SCSI Commands.

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Quantum DLT 4000 Manual Pagina 63