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The AHA-1740A/1742A/1744 supports asynchronous, synchro-
nous, and Fast SCSI data transfers on the SCSI bus. Asynchro-
nous data transfers support up to 2 MBytes/sec, synchronous
transfers support up to 5 MBytes/sec, and Fast synchronous trans-
fers support up to 10 MBytes/sec. Devices using different trans-
fer rates can all be used on the same SCSI cable. The
AHA-1740A/1742A/1744 is both SCSI-1 and SCSI-2 compatible,
and supports both SCSI-1 and SCSI-2 devices.
The AHA-1740A/1742A/1744 fully supports the SCSI features of
disconnect/reconnect, zero latency reads, and tagged queuing. Dis-
connect/reconnect support maximizes SCSI bus utilization for
multiple target systems. Zero latency reads and tagged queuing
minimizes the mechanical limitations of SCSI fixed disk drives.
The AHA-1740A/1742A/1744 has an on board BIOS that allows it
to be used in addition to, or in place of, a standard fixed disk con-
troller. Thus, up to two SCSI fixed disk drives can be used under
DOS without the use of device drivers. Up to seven SCSI fixed
disk drives can be used without a driver if MS-DOS 5.0 or higher
is used. Booting is also supported by the BIOS in the DOS envi-
ronment.
The AHA-1740A/1742A/1744 fully supports scatter/gather, a fea-
ture utilized by device drivers to minimizes the number of I/O
commands into memory. The UNIX
®
/XENIX
®
and NetWare
®
op-
erating environments take advantage of this feature.
The AHA-1740A/1742A/1744 has two modes of operation: stand-
ard mode and enhanced mode. The standard mode is software
compatible with the AHA-1540 series host adapter drivers. The
enhanced mode uses an advanced, high performance mailbox
interface and features full EISA 32-bit addressing. The
AHA-1740A/1742A/1744 in enhanced mode can support up to
4 Gigabytes of host RAM memory, while standard mode is limited
to 16 MBytes of host RAM. The operation mode of the
AHA-1740A/1742A/1744 is selected by running the EISA Configu-
ration utility program provided with every EISA machine. The
modes of operation are fully described in Chapter 6, Host Adapter
BIOS Operation.
adaptec AHA-1740A/1742A/1744
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