Emulex MD21/S2, Техническое руководство

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Section 1
INTRODUCTION
1.1 OVERVIEW
The MD21/S2 Disk Controller is a single-board controller designed
to interconnect Small Computer System Interface (SCSI) host
adapters and controllers to one or two Enhanced Small Device
Interface (ESDI) ,5.25-inch Winchester disk drives. The controller
features the single-ended SCSI option for drivers and receivers.
For brevity, the reference MD21 will be used throughout this
manual.
In combination with an independent host adapter, the SCSI bus
allows a wide variety of computers to interface with the MD21
Controllers. Compatible computers include IBM Personal Computer
systems such as the IBM PC-XT, Q-Bus, VMS Bus, VAX UNIX, and
Multibus-based computers. Up to eight bus devices, in any
combination of host systems and intelligent controllers, can be
supported by the SCSI bus. The MD21 Controller, in combination
with one or two ESDI 5.25-inch magnetic disk drives, provides a
low-cost, compact storage subsystem.
The MD21 Controller's architecture and SCSI features it supports
make it an ideal building block for use by OEMs and system
integrators. The MD21 Controller supports a powerful set of SCSI
commands. By using those commands, an efficient multiple-initiator
configuration can be constructed with the support of the disconnect
function. (The disconnect function allows the MD21 Controller,
when it is performing a time-consuming task, to release the SCSI
bus temporarily and reconnect at a later time when the task is
complete.) The MD21 Controller supports all required SCSI commands
and the SCSI Common Command Set (CCS) for direct-access devices
described in the CCS standard.
Emulex currently offers other SCSI bus microcontrollers that can be
used with SCSI bus subsystems. These include the MT02/MT03 and the
MD01. The MT02/MT03 Tape Controller interfaces the SCSI bus to a
5.25-inch streaming cartridge tape drive. The MD01 Disk Controller
connects one or two ST506 interface 5.25-inch disk drives to the
SCSI bus. Also, the MD23/24 Disk Controller interfaces the SCSI bus
to up to four ESDI single-ended/differential drives and the MD32
connects up to four SMD/SMD-E drives to the SCSI bus.
In addition to basic stand-alone controller products, Emulex also
offers complete SCSI bus disk and tape packaged subsystems for
microcomputer applications.
Introduction 1-1