Chapter One Introduction; Document Scope; Purpose - Adaptec AHA-1740A Technical Reference Manual

Chapter One
Introduction

Document Scope

This manual provides information on installation and defines the program interfaces
of the AHA-1740A/1742A/1744 intelligent host adapters in EISA bus-based systems.
Programming peripheral drivers directly to the hardware interface of the board is not
recommended. The ASPI (Advanced SCSI Programming Interface) specifications pro-
vide a simpler and more flexible interface which is protected against changes, up-
grades and obsolescence of the boards.

Purpose

The Adaptec AHA-1740A/1742A/1744 provides a powerful multitasking interface be-
tween the Extended Industry Standard Architecture (EISA) bus and the Small Com-
puter System Interface (SCSI) bus.
The AHA-1740A/1742A/1744 is a high-performance intelligent host adapter which
supports a maximum asynchronous SCSI rate of 2.0 MBytes/second and a synchro-
nous transfer rate of 10.0 MBytes/second. It supports multithreaded I/O operations,
allowing simultaneous operations on multiple targets/LUNs. Disconnect/Reconnect
support maximizes bus utilization for multiple target systems. Target mode opera-
tion allows the AHA-1740A/1742A/1744 to receive information from other host adapt-
ers. Scatter/Gather allows high performance even in systems with fragmented
memory buffers.
The AHA-1740A/1742A/1744 provides a solution for system applications requiring
very high performance, configuration flexibility, multithreaded I/O capability, and
system redundancy. The Adaptec BIOS also allows the AHA-1740A/1742A/1744 to be
used in place of a standard hard disk controller.
The AHA-1740A/1742A host adapter provides high-performance host adapter cir-
cuitry connected to the more common single-ended SCSI bus. The SCSI specification
recommended maximum cable length for 5 MBytes/second synchronous data transfer
is 6 Meters, or about 20 feet.
The AHA-1744 host adapter provides identical host adapter circuitry, but connects to
a differential SCSI bus. The SCSI specification recommended maximum cable length
for 5 MBytes/second synchronous data transfer is 25 Meters, or about 82 feet.
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