Hewlett-Packard SureStore 125ex Optical Jukebox User's Guide - C1118-90000

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OPERATING THIS JUKEBOX ON A
SCSI BUS
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BOp erating This Juke box on a SCSI Bus
A BRIEF OVERVIEW OF SCSI
GENERAL
The Small Computer System Interface (SCSI), is a contention-based bus that accommodates different speed devices
without impacting the devices with faster transfer speeds. This specification was defined by the American National
Standards Institute (ANSI) in 1986. The specification defines both the physical medium and the command set used to
transfer information. Later developments are known under the newer specifications, SCSI-2 and SCSI-3.
THE SCSI BUS
The common SCSI buses are 50-pin and 68-pin. The 50-pin bus, which uses eight of its lines for data transmission, is
called a “narrow” bus. The narrow bus can support eight devices. The 68-pin bus, which uses 16 lines for data transmis-
sion is called a “wide” bus. The wide bus can support 16 devices.
Some devices may have 68-pin connectors, but operate with a “narrow” bus. (See the next section in this Appendix,
“The SCSI Bus and This Jukebox”.
INITIATORS AND TARGETS
SCSI devices on the bus are either “initiators” or “targets.” An initiator (usually the host computer) originates a transac-
tion and the target (usually a peripheral device) fulfills the request.
Initiators and targets identify themselves on the bus by a SCSI ID. The ID is designated by the user and is set electroni-
cally or manually depending on the device. In addition to identifying a device on