Adaptec AHA-1740A user manual BIOS Operation Modes, 2. AHA 1740A/1742A/1744 Operation Modes

EISA-to-Fast SCSI Host Adapter Overview

BIOS Operation Modes

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. The two modes of the AHA-1740A/1742A/1744 are selected by running the EISA Con- figuration utility provided with every EISA machine. In general, the enhanced mode of the AHA-1740A/1742A/1744 should be used, whenever possible, for maximum performance.

The two operation modes are described in the table below.

Table 1-2. AHA 1740A/1742A/1744 Operation Modes

Standard Mode	Enhanced Mode
(ISA compatible mode)	(enhanced mailbox interface)
32-bit host transfers at 33 MBytes/sec.	32-bit host transfers at 33 MBytes/sec.
Addresses up to 16 MBytes host RAM.	Addresses up to 4 Gigabytes host RAM.
AHA-1540 series mailbox structure	New high performance mailbox
(compatible with AHA-1540 software).	structure.
Supports Fast SCSI devices up to	Supports Fast SCSI devices up to
5 MBytes/sec.	10 MBytes/sec.
Boot only from SCSI ID 0.	Boot from any SCSI ID.
Drives spin up only at power-on.	Drives spin up at power-on, or from
	SCSI Start Unit command.
Disconnect/reconnect, parity checking,	These parameters can be enabled or
and synchronous negotiation enable or	disabled on a per target basis.
disabled for all SCSI targets.
Up to four host adapters can be in-	Up to twelve host adapters can be
stalled in the system.	installed in the system.
BIOS support for drives up to 1 Gi-	BIOS support for drives up to 8
gabyte in capacity under MS-DOS.	Gigabytes in capacity under MS-DOS
	5.0 or higher.
BIOS support for a maximum of 2	BIOS support for up to 7 SCSI drives
SCSI drives.	(using MS-DOS 5.0 or higher).

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