Adaptec AHA-1740A - Manual (Page 15)

Chapter One
Overview
This User Guide provides software installation information for
the Adaptec AHA-1740A, 1742A, and the 1744 EISA-to-fast-SCSI
bus master host adapters. Cumulatively the cards are referred to
as AHA-1740A/1742A/1744 in this guide. The Adaptec
adl.exe
download utility and the ASW-C174 and ASW-M174 software
packages are described, as well as available software support.
General Product Information
The AHA-1740A/1742A/1744 provides a high performance connec-
tion between the EISA (Extended Industry Standard Architec-
ture) bus and the SCSI (Small Computer System Interface) bus.
The AHA-1740A/1742A are single-ended SCSI host adapters that
support single-ended disk drives. Single-ended host adapters and
devices can support cable lengths of up to 6 meters (about 18
feet). Most of the SCSI drives on the market today are of this
type. The AHA-1744 Host Adapter is a differential SCSI host
adapter that supports differential type SCSI devices. The use of
differential SCSI drives and adapters allows the SCSI cable
length to be up to 25 meters in length (about 75 feet). Other than
this basic difference, and other slight differences discussed in this
document, the AHA-1740A/1742A/1744 are installed and operate
identically.
The AHA-1740A/1742A/1744 is a bus master device and transfers
data into host memory at burst rates of 33 MBytes/sec. These
transfers are generally 32 bits wide, unless transferring data into
8- or 16-bit memory. This form of transfer is known as bus mas-
ter DMA (Direct Memory Access). Bus mastering minimizes host
CPU overhead, since the AHA-1740A/1742A/1744 has an on board
processor to transfer data directly to memory. This is the highest
performance type of data transfer available for the EISA bus in
multitasking operating systems.
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